In the brink of extinction - many freshwater fish

Tiistai 12.12.2023 klo 17.23 - Mikko Nikinmaa

When I did my Ph.D. thesis 40-45 years ago, the topic: effects of temperature and hypoxia on respiration of rainbow trout, was hardly noticed by the general public. In 1976 we, biology students arranged a theme evening about the pollution of the Baltic  Sea and invited media. Nobody came, and when I asked a newspaper reporter why that was the case, he answered that the topic had no general interest. I wish the situation were the same today: fish would not suffer from pollution, increased temperature and decreased oxygen level. Unfortunately that is wishful thinking.

IUCN (International Union for the Conservation of Nature) has recently updated its Red List with very worrying information of fish, particularly freshwater fish. A quarter of the freshwater species is in immediate danger of extinction. The most important proximate cause is pollution, but toxicant effects cannot be separated from temperature increases and eutrophication, which causes oxygen lack. All of the previous problems increase parasite loads and cause fish diseases. In addition, overfishing and building of waterways, which has destroyed spawning sites or made it impossible to reach them, decreases fish populations.

Below I give a couple of examples of how all of the above cause the disappearance of specific species. First, eels are critically endangered species, which are characterized by their catadromous way of life and long spawning migrations. They grow and reach maturity in freshwater. Their migration from sea to freshwater feeding sites is critically dependent on smell sensing, which is dramatically disturbed by pesticides and metals. Consequently, those types of pollution may be an important cause of declining eel populations. Second, burbot is a coldwater fish. It spawns in the middle of winter, and it is ice-fished in January-February to get the fish and its eggs for soup. Now that the temperature is increasing, burbot is already living at the high end of its temperature tolerance, and may soon become extinct. Another group of coldwater fish is salmon and its relatives. In addition, it requires clear water with high oxygen content. Since both an increase in temperature and eutrophication decrease the oxygen level, salmon and its relatives may become extinct. Lampreys have succeeded in temperate waters for 500 000 000 years. Many of the species live in sea as adults, but spawn in rivers. Because of building of waterways, e.g. hydroelectric power plants, their long saga may be coming to the end. Finally, aquarium hobby is very popular throughout the world. Many of the ornamental fish do not reproduce in captivity, and are thus fished wild. This has made many species endangered because of overfishing.


Kommentoi kirjoitusta. Avainsanat: environmental pollution, climate change, overfishing, eel, salmon, oxygen, hypoxia

Aquaculture can be a sustainable food source

Maanantai 23.10.2023 klo 14.02 - Mikko Nikinmaa

Overfishing is a threat to aquatic biodiversity. The worst sceneries predict that a massive flood of fish extinctions occurs in this century, if commercial fishing is continued at its present level. This is a major problem, as it occurs at the same time that the need for animal protein in our food should change from the traditional mammals (cattle, swine and sheep) towards poikilotherms. A production of flesh kilogram requires only about 1/10 of energy in poikilotherms as compared to mammals. Because of this, they are a much preferred food source compared to traditional farm animals, when we are faced with problems with land use, climate change and biodiversity loss. Of poikilotherms fish are by far the most acceptable food – virtually everyone has eaten them, whereas the alternatives, insects, snakes, crocodiles etc. all are disliked by several people or are difficult to culture.

So, aquaculture could be a way forward to provide the world with animal protein in a sustainable fashion. However, that would not be the present way of aquaculture. There are presently many reasons why aquaculture is not sustainable. First, most cultivated fish are predators, such as salmonids. Their feed is usually fish flour-based. So, it does not decrease overfishing, the only change is that one can fish species, which would not be preferred human food.  Second, fish are cultured especially in marine net cages at high densities. Feeding therefore causes local eutrophication and the fish are not subjected to normal activity. Third, to prevent parasites and diseases in the high-density environments, a lot of medications are used. These affect the ecosystems in the vicinity of the cages. For example, one of the major parasites of salmon is salmon louse, a copepod. Its treatment affects all crustaceans in the vicinity of the net cage. Thus, lobster stocks may suffer. It should be noted that all fish diseases are favoured by the high fish densities in the net cages. finally, the fish in the net cages do not get the same amount of exercise as wild fish. Because of this, if fish are reared for stocking, their survival is likely to be reduced.

The reason why aquaculture has mainly been in sea bins is naturally the cost – the profit is maximized at the cost of the environment. However, shouldn’t we start putting environment first in order to keep the world in reasonable condition. Sustainable aquaculture is presently possible. Instead of cultivating fish in sea cages, they could be kept in tanks in dry land. In such tanks water flow can be kept directional and all the waste collected before it enters the sea, rivers or lakes. If need be, water purification similar to normal municipal wastes could be applied. Instead of the fish flour, flour made of insect maggots could be used. Maggots can be grown in bulk quantities already today.

By these means the salmonid aquaculture would be made sustainable. Increasing the number of fish species cultivated in large amounts one could also combine, e.g., rice production and aquaculture or vegetable production and aquaculture.

Kommentoi kirjoitusta. Avainsanat: climate change, biodiversity, fish feed

Fish in high-flow zone of rivers may be the first victims of climate change

Maanantai 25.9.2023 klo 18.56 - Mikko Nikinmaa

Fish living in high-flow areas of rivers have chosen (or evolved in) that habitat, because they need a lot of oxygen for their high activity. Flowing water becomes well oxygenated, as it is continuously exposed to air. However, the amount of oxygen taken up by water decreases with increasing temperature, simultaneously as poikilothermic fish need more of it, as temperature increase speeds up their metabolism.

If temperature increases enough, fish heart cannot pump enough oxygenated blood to sustain metabolism. This we have clearly shown in our article Anttila et al, Comp Physiol Biochem A 275, 111340 (2023). Although the study was done on seabass, the principle holds also for river fish. The amount of oxygen initially reaching the gills, where it is taken up, further decreases the maximal temperature the fish can tolerate.

Zhi et al (Nature Climate Change 2023; have shown that the oxygen level in rivers throughout Europe and United States has decreased for the past forty years. While increased temperature was the main driver, the oxygen level decreased more than expected because of temperature increase. It is possible that the general eutrophication with increased oxygen consumption.

Regardless, associated with the physiological response to increased temperature of fish, the temperature-caused decrease in maximal amount of oxygen the water holds, can cause extinction of salmonids living in the fast-flowing head streams.

Kommentoi kirjoitusta. Avainsanat: temperature, oxygen, fish physiology, cardiovascular function

Hypoxia - a problem for aquatic environments

Maanantai 15.5.2023 klo 13.46 - Mikko Nikinmaa

When I started my scientific career about forty years ago, I concentrated on the effects of increased temperature and hypoxia on oxygen transport in fish. At that time the topic was not considered to be of general interest. Things have changed since then. In 1970’s oxygen minimum zones were a peculiarity in the oceans. Today their occurrence has increased markedly making them a grave threat to the well-being of aquatic fauna. The increased occurrence of oxygen-minimum zones occurs together with climate change and ocean pollution.

Aquatic environment always requires very effective oxygen uptake, because water can contain very little oxygen – at sea level about the same amount as air in about 20 km’s height – it is hard to breathe, and the few oxygen molecules present in water move slowly. For active aquatic animals the added problem is to be able to release enough oxygen to working muscle. In the situation of hypoxia occurring together with increasing temperature, active fish and crustaceans are not able to coupe. Consequently, large areas of oceans become devoid of animals. Since those animals are the preferred foodstuff of man: salmonid species, cod, tuna, lobster, shrimp, the spreading of hypoxic areas causes the lack of seafood.

The problems with obtaining enough seafood comes at the same time as man should increasingly shift from eating cattle and sheep, i.e. homeotherms, to eating fish and other poikilotherms in order to combat climate change. Climate change itself makes doing this difficult. Also, the oceanic biodiversity is at risk, since the habitats of many species become unsuitable for them to thrive in.

Kommentoi kirjoitusta. Avainsanat: climate change, fish, seafood

Aquatic pollution is still a serious issue

Tiistai 28.3.2023 klo 15.53 - Mikko Nikinmaa

 In 1970’s and 80’s rivers were little more than sewage channels, and most waste water was pumped out to lakes and seas virtually uncleaned. If strands started to get littered, the solution was to make sewage pipes longer. A standing “joke” was that Americans built holiday resorts to Central America so that whenever the beach started to suffer from municipal pollution, that resort was left to locals and a new one built elsewhere. The polluted rivers could catch fires and fish deaths were common. In the Baltic Sea at least 70 % of the seals could not reproduce, almost causing extinction of Baltic seals.

One would have thought that humankind would have learnt from the problems of the past. But no. Profit is still the major goal; environmental actions are only done, when immediate financial gain would suffer from not doing them. Admittedly, water purification has been much improved in the industrialized countries in fifty years. In part, however, this has meant that the most polluting industry has been relocated to countries with lax environmental regulation. Some rivers in India have so high antibiotic levels that a patient could get a daily dose of medicine by drinking river water, others in Pakistan have so high effluent load from tanning industry that the water colour shows which dye is used most in the textiles. Even in our Western World, many improvements are not real. When it became clear that chlorinated compounds were highly toxic, they were banned. The chemical industry then started producing new fluorinated compounds. Anyone with reasonable knowledge of chemistry could have predicted that since fluorine and chlorine are sister elements, also fluorinated compounds are very toxic. This conclusion was finally reached, and several fluorinated compounds are banned. The insecticide use all over the world has increased, and one of the problems in their use is, if a sweeping generalization is made, that they are much more toxic to aquatic animals than to insects. Also, an occasional spill of toxic substances to rivers still occurs. Add climate change on top of all that, and the present-day situation emerges. The reason for including climate change is that first, the increase in temperature is a stress, and combined with contaminant-induced stresses can cause mortality, and second, climate change causes marked variations of river flow (because of alternations between heavy rains and dry periods) whereby the contaminant flow, e.g., from agriculture becomes highly pulsatile.

One sees the results in the news items. There have been massive fish mortalities in many shallow European lakes and in sea areas at Australian coast. Gold mining effluents have caused fish mortalities in Amazonas area and in Danube. The river Oder (in Poland) experienced major mass mortality of fish last summer and Murray and Darling rivers (in Australia) just recently. While the ultimate reason of neither is clear, agricultural toxicants together with climate change have likely contributed. About 30000 l of styrene leaked last Friday to a tributary of Delaware river, where Philadelphia obtains its drinking water, making it unsuitable for human use for a few days…These are just a couple of examples, it appears that there is an issue with aquatic pollution more or less every day somewhere in the world.

Kommentoi kirjoitusta. Avainsanat: fish mortality, climate change, multiple stresses, insecticides

Heart function and individual variability play major roles in temperature tolerance of fish

Maanantai 14.11.2022 klo 14.42 - Mikko Nikinmaa

Climate change has major effects on fish, especially fish in lakes, since the whole water body can warm up as a result of long-lasting heat waves. Because of the uniform temperature regardless of the depth, fish cannot seek colder temperatures near the bottom. As a consequence, massive fish mortalities occur in shallow lakes of temperate zone every summer nowadays.

The reasons, why fish die as a result of increased temperature can only be understood by studying the functional changes occurring as a result of temperature elevation. Thus, physiological studies should be in the centre of climate change studies. If the reasons for vulnerability to increased temperature are known, it can also be estimated, which measurable responses predict fish mortalities. This as a background, and recognizing that individual variability of fish determines why some die and others remain living, we studied how fish tolerant and intolerant to high temperatures differed from each other. The results of the extensive studies are reported by Anttila et al in Comparative Biochemistry and Physiology (//

Our results show that for a given age group, heart function is decisive in determining temperature tolerance. The efficiency of heart is markedly different in different individuals, whereby marked individual variability in temperature tolerance occurs. Thus, in predicting the effects of climate change on fish populations, we should not restrict our analysis to the mean response but also to the variability observed. In future it must be evaluated to which extent the thermal tolerance and its variability are heritable, as this will have significant impact on the vulnerability of species to global warming.

Kommentoi kirjoitusta. Avainsanat: climate change, fish biology, temperature acclimation, heat wave, fish mortality

The thermal tolerance of fish is not increased by 40-45 years of exposure to increased temperature

Sunnuntai 25.9.2022 klo 18.42 - Mikko Nikinmaa

The waters in the vicinity of nuclear power plants give a possibility to investigate how increased temperature affects fish populations. Nuclear power plants use ambient water to cool down the units where energy is produced. The cooling water is returned to the environment. As a consequence the water in the vicinity of the power plant is 2-5oC higher than in the environment generally. In Finland, nuclear power has been produced 40-45 years, so organisms have experienced the increased temperature for that period of time. Both the temperature increase and the duration of exposure are similar to what can be expected to occur as a result of climate change.

In her Ph.D. thesis, which is defended on September 30, 2022, Giovanna Mottola used this natural exposure to evaluate, if the 40-45-year exposure was able to improve the thermal tolerance of stickleback. The results indicate first, that regardless of the previous exposure history, a short heat wave increases the highest temperature tolerated acutely, and second, that previous history of living in the high temperature of the vicinity of nuclear power plant does not affect the temperature tolerance as compared to non-exposed fish. This means that fish living at an increased temperature are closer to the tolerance limit than fish living in cooler temperatures, and if a heat wave occurs, are consequently more likely to succumb. Although the studies are only on one species, similar results have been observed with the couple of other species so far studied. This suggests that the upper thermal tolerance of a given species is fixed and cannot be evolutionary increased within the time window available in climate change scenarios.

If one then considers on the basis of the natural laboratory data the ecological status of fish populations in the climate change scenarios, it appears likely that marked disappearance of fish occurs, before the migration of more temperature-tolerant, southern fish occurs. This will be true because of the time constraints of movement. Also, coastal fish are not likely to cross open water areas, so in their case the northward migration of southern populations is further slowed down.

Kommentoi kirjoitusta. Avainsanat: climate change, fish populations, temperature acclimation

Human actions cause climate change even when fossil fuel use is not involved

Tiistai 22.3.2022 klo 18.24 - Mikko Nikinmaa

Although there are still many people thinking that climate change is not occurring or at least man has nothing to do with it, there are many problems that man is causing which accelerate temperature increase, and which could be avoided by human action. The points below are such, and can be very important in driving many parts of the world uninhabitable because of either too high temperature or drought or both. So, even people who do not believe that fossil fuel burning causes temperature increase, should accept that the following affect climate and that humans could take actions to combat the changes.

1. Because of massive deforestation, Amazon rainforest appears to near tipping point, where the rainforest turns to savannah. Boulton et al write in recent Nature Climate Change (Nature Climate Change 12: 271-278; 2022) how the resilience of Amazon rainforest has decreased dramatically since the early 2000s. Other studies have also indicated that whereas we have always considered Amazonas to be a carbon sink, it has recently turned into a net emitter of carbon dioxide. The major reason for carbon dioxide emissions is the widespread forest burning.

If the rainforest starts turning to savannah, naturally the first thing that happens is that the plant and animal species living in rainforest die off, so the biodiversity decreases radically. But even if this doesn’t concern the people, who deforest Amazonas, the following should. The water cycle of South America depends on the rainforest. If Amazonas turns into savannah, because more agricultural land is wanted, the whole South America dries up, and many areas become unsuitable for agriculture (too dry). So, by trying to increase agricultural area, greedy people end up decreasing it.

And because of the loss of one big carbon dioxide sink, the temperature throughout the world increases even if fossil fuels had nothing to do with climate change.

2. Two events happening to the oceans are also causing increased carbon dioxide levels and consecutive temperature increase even without the input of fossil fuel burning, and both depend mainly on human action. First, almost a half of the photosynthetic carbon dioxide use is due to the photosynthesis of (mainly unicellular) algae. Because of the pollution, it is estimated that the oceanic photosynthesis has decreased by 10-15 %. This increased carbon dioxide load is one factor affecting global temperatures, and could be avoided by human action – proper water purification. Second, world’s oceans are overfished. The global carbon cycle depends a lot on fish accumulating carbon. When they die, the accumulated carbon sinks to the bottom of the oceans and stays there for thousands of years. As overfishing reduces fish populations, this removal of carbon from ocean surface is reduced, and the reduced removal is seen as an increase in global carbon dioxide level, leading to temperature increase.

Again this takes place without any change in fossil fuel use, but is entirely human-caused.

3. There are further a couple of vicious circles, which increasingly take place, if human actions fail to limit temperature increase. Temperature increase decreases the carbon dioxide solubility in water. Thus, if temperature increases, more carbon dioxide is given up from the ocean, leading to further temperature increase etc. There are huge natural gas (methane) stores below the permafrost. Methane is a very potent greenhouse gas. If temperature increases so that permafrost starts melting, the methane below is liberated, causes further temperature increase leading to further permafrost melting and methane liberation etc.

To prevent these vicious circles from happening, climate deeds are important even today with the brutal Russian attack to Ukraine. In the best case, it can actually speed up the change from fossil fuel-based to green energy production.

Kommentoi kirjoitusta. Avainsanat: carbon cycle, Amazonas, deforestation, overfishing, permafrost, methane

Temperature increases faster than fish can adapt

Tiistai 29.12.2020 klo 16.28 - Mikko Nikinmaa

A temperature increase will affect fish populations everywhere. Depending on the species, the depth of the aquatic body and its accessibility the effects can be drastic – the most extreme outcome being  the total disappearance of the fish from the habitat. Because of this, the research on temperature biology of fish has become an important field of study in climate change research. The importance of fish studies is strengthened, as they can be an primary source of animal protein in food.

Fish can be either stenothermal or eurythermal. The definitions indicate the phenotypic plasticity of species with regard to temperature. Stenothermal species tolerate only small temperature changes, whereas eurythermal species can live in wide temperature range. It should be noted that most of the preferred fisheries species have narrow genotypic temperature tolerance. If they live in environments with different temperatures, their genotypes are different, each still having narrow temperature tolerance so that the cold-temperature genotype would not be able to tolerate the temperatures that the warm-temperature genotype lives in and vise versa. Although a temperature increase may actually increase the amount of fish flesh produced per unit time, the species accounting for the increased productivity are not preferred catch or food.

The roles of phenotypic plasticity and the speed of heritable genetic adaptation to temperature changes has been surprisingly little studied. 


Further, it is almost completely unknown, if the temperature tolerance is affected by environmental contaminants. One important recent study with zebrafish (Morgan et al. PNAS 2020: suggests that the genetic adaptation to increased temperature is not fast enough to keep pace with the temperature increase that is currently occurring. It also appears that the plasticity of tolerated temperatures decreases, when the population adapts to increased maximal temperature.

So, this is bad news throughout. The fish that we like to eat are stenothermal. The eurythermal species could substitute for them, but even they have problems in genetic adaptation. Furthermore, it seems that tolerance to reduced temperature evolves faster than that to increased temperature. All of these points make the case for markedly slowing down and stopping the current temperature increase stronger. If we want to eat fish, climate change must be stopped.


Kommentoi kirjoitusta. Avainsanat: climate change, fisheries, phenotypic plasticity, genetic adaptation

Environmental effects are complex; that is the problem

Torstai 15.10.2020 klo 14.19 - Mikko Nikinmaa

In any natural environment all animals, here I am focusing on fish, experience changes in temperature, parasite infections etc. On top of that become all the anthropogenic contaminants, metals, pesticides, flame retardants, pharmaceuticals, personal care products and so on. The complex cocktail can affect organisms directly and indirectly, and a change in any variable can affect the growth, health and survival of them.gudgeon.jpg

Because it is very difficult to study, how the environmental heterogeneity and its changes affect animals, most studies use a defined set of abiotic conditions and one pollutant. While this gives much valuable information, it should be remembered that for example a change in temperature, oxygen level, age of animal, salinity of water and the presence of other contaminants can influence the observed result. Occasionally, one gets the surprising finding that what we think as a pollutant and thus expect a negative effect actually increases the tolerance to an environmental change. For example, when we studied the effects of oil pollution on the thermal tolerance of juvenile fish (rainbow trout and European sea bass), we observed that the oil-exposed fish, if anything, tolerated high temperature better than control specimens (Anttila et al 2017, Environ Sci Pollut Res DOI 10.1007/s11356-017-9609-x). Recently, Petitjean et al (Science of The Total Environment Volume 742, 10 November 2020, 140657) have studied gudgeons in six French rivers, and observed clear interactions between the metal loads and temperatures the fish experience: an increase of metal load at high temperature reduces growth. Naturally, this survey conducted in natural environment cannot differentiate between direct and indirect effects of metals. It remains as a possibility that, e.g., the prey organisms of the fish are affected initially, whereby their availability decreases, decreasing the growth of fish.

Here I have focused on temperature, because we are currently undergoing a giant-scale natural event, climate change. It would be much simpler to evaluate, how temperature increase as such affects living functions, than take into account how temperature change affects responses to the mixture of environmental contaminants. The temperature effects can be completely opposite for different contaminants.

Kommentoi kirjoitusta. Avainsanat: climate change, environmental pollution, toxicant, cocktail effects, fish, temperature

Rising temperature affects fish more than previously thought

Lauantai 15.8.2020 klo 21.02 - Mikko Nikinmaa

A recent study in Science (Dahlke et al., Science 369, 65–70, 3 July 2020) has evaluated, how fishes are affected by temperature increase associated with climate change. Fish are an increasingly important food source for humankind, so their success in warming waters is of primary importance for feeding human population. Consequently, the ability of fish to tolerate warming waters has been studied intensively. Earlier, it has been estimated that only 5 % of fish populations would be adversely affected by temperature increase predicted to occur by 2100. A lot of fisheries experts have sucked of relief about this, as overfishing

Lampotilan_Sieto.jpgis a major threat presently, and it is thought that overfishing may decrease fish populations by half before 2050. In fact, it has been estimated that temperature increase would make population sizes of fishes larger in some areas.

The limitation of earlier estimations has been that the possibility that possible differences between temperature tolerances of age groups have not been estimated. This was done in the study by Dahlke et al. The results show that temperature tolerance of different age groups of fish is markedly different. The embryos (developing fish within egg cases) and spawning adults (blue and black lines in the figure) appear to have up to 20oC smaller tolerated temperature range than free-swimming larvae or non-reproducing adults (red and orange lines). The difference is greatest at mid latitudes, and decreases both (and especially) in the arctic and near equator.

The reason for decreased temperature tolerance is probably due to mismatch between oxygen uptake and consumption. Oxygen uptake is limiting in the embryos enclosed within eggs, whereas the oxygen transport of free-living larvae and juvenile and non-reproducing adults becomes more effective. In spawning adults the oxygen consumption increases without improvement of oxygen transport. Physiological studies about the interaction between temperature, oxygen transport and consumption are needed in different life stages of fish to enable conclusive evaluation of what causes life stage-dependent variation of temperature tolerance.

Regardless of the reason, it can be estimated that almost half of the fish stocks will be adversely affected by the temperature increase taking place, if the present international agreements are fulfilled. Together with the reduced stocks because of overfishing this can result in marked reduction in the fish food available to humankind. However, if we would do appropriate climate actions, one could prevent virtually all effects on fish populations.

Kommentoi kirjoitusta. Avainsanat: climate change, fisheries, oxygen transport

Cod - a component of fish'n chips disappearing because of climate change?

Keskiviikko 8.7.2020 klo 14.27 - Mikko Nikinmaa

In an effort to introduce some physiological realism to stock assessments, Hänsel et al. (Ocean warming and acidification may drag down the commercial Arctic cod fishery by 2100; PLOS ONE, April 22, 2020) have modelled how some factors caused by temperature increase and ocean acidification affect traditional stock modelling of cod. Although at crude level (e.g. not taking into account any effects of aquatic pollution), the study gives sobering views. While up to the present an increase in temperature has been beneficial for recruitment, the future looks gloomier. Because of the improved recruitment until the bottom temperature reaches +5oC, cod stocks have actually increased with temperature increase. However, now the bottom temperature in most cod fisheries areas is beginning to be above that temperature, whereby further temperature increase causes reduced recruitment. Also, ocean acidification reduces recruitment. The modelling suggests that because of temperature increase and ocean acidification, cod catches, which could at present be sustainable, lead to rapid loss of cod populations by 2100.

The predictions by Hänsel et al give a very strong reason, why understanding the physiology of fisheries species is imperative for planning sustainable fisheries.

Kommentoi kirjoitusta. Avainsanat: stock assessment, fisheries, ocean acidification

Physiological studies add a predictive component to modelling fish stocks

Perjantai 3.7.2020 klo 18.00 - Mikko Nikinmaa

Mirella Kanerva, Kristiina Vuori and us others have recently published a study about the  fitness of salmon during their feeding migration in different parts of the Baltic Sea (Kanerva et al. Environmentally driven changes in Baltic salmon oxidative status during marine migration, Science of the Total Environment, in press, The study is logi.jpgextremely difficult, since it tried to evaluate, how the physiological status of a commercially important fish species in natural environment is affected by food, water temperature and environmental pollution. It is noteworthy that we were able to show that factors affecting the oxidative status of the fish affected the fitness and seawater survival of the salmon. It was also possible to show that increased toxicant load, elevated temperature and cyanobacterial blooms already in the present Baltic Sea induce changes, which are measurable with physiological parameters, and are likely to affect recruitment of salmon.

The point about physiological measurements being able to predict changes in fitness and recruitment is revolutionary for fisheries biology. This is because earlier one has based all the models for stock estimations on retrospective observations on catches and spawning success. The findings of our study indicate  that physiological expertise can add a predictive component to recruitment models.

Our results also indicate, which parts of the Baltic Sea are most contaminated affecting the oxidative status of salmon. It is no surprise that effects are observed in the Gulf of Finland. However, these findings show that similar parameters could be used elsewhere to evaluate, if environmental contamination is serious enough to affect preferred fisheries species. Again, this adds a predictive component to earlier estimations based on retrospective data.

Hitherto, fish physiology has remained a small field, but our results indicate that it could play a major role in modelling fish stocks, because it adds a predictive component to models and thereby gives possibilities for more rapid fisheries decisions than are currently possible.

Kommentoi kirjoitusta. Avainsanat: fisheries biology, stock estimation, environmental pollution, oxidative stress

Australian bushfires are over, but not the harm to the animals

Tiistai 11.2.2020 klo 16.00 - Mikko Nikinmaa

During the worst bushfires ever in Australia, millions of terrestrial animals have died, burned alive. The newscasts throughout the world have shown koalas with bad burns being rescued, only few out of the many which died in the fires. Among the species which have suffered most, koala is probably the first, since the habitat of koala is the most likely to suffer from fires, and the animals are not fast, and therefore cannot escape the fires.

The fires finally have ended now, because very heavy rain has fallen in Eastern Australia. In New South Wales the rain has been heaviest in thirty years. It has rained in 24 hours (February 8-10, 2020) as much as in one and a half months in a normal year this time. The heavy rain has brought record floods, which have followed record drought. Unfortunately this is exactly what the climate researchers have predicted; as a result of climate change droughts and heavy rains both occur, the weather becomes very unpredictable and extreme phenomena occur. This is also seen in Europe: in Central Norway one mIMG_20170808_0007.jpgeasured +19oCn early January and it snowed 20 cm in Madrid in the late January while grass is green in Southern Finland.

The bushfires of Australia have been extinguished by the heavy rain, and firemen and terrestrial animals can suck of relief. Now it is the turn of aquatic animals to suffer. The rains take the ash and any chemicals that were used in firefighting to the rivers. One has already seen the consequence of this in tens of thousands of dead fish all over the place. Since Australia has very little inland water, the aquatic fauna is quite vulnerable and can easily become extinct. There are two major reasons for fish deaths. First, many of the chemicals used in extinguishing the fires are quite toxic. For example, chemicals of extinguishing foam contain fluorocarbons and aluminium sulphate, which are quite toxic. Aluminium ion was considered to be the major reason behind fish deaths during the acid rain period in Europe and North America in late 20th century. However, in the leachate from bushfires, the chemical load is probably of only very minor importance. The ash reaching the rivers consumes the oxygen, and the fish living in running water usually require well-oxygenated water. When the ash, which contains organic carbon, uses up the oxygen, and renders the water hypoxic, the fish die of oxygen lack. What is worse, there is nothing that can be done to prevent fish deaths: they are the ultimate consequence of bushfires and heavy rain. The only thing we can do is to wait and hope that an adequate number of fish survive for the populations to recover within 5-10 years.

Kommentoi kirjoitusta. Avainsanat: climate change, hypoxia, fish deaths, Australian bushfires

Faunal Mortality in Caribbean

Tiistai 19.11.2019 klo 18.33 - Mikko Nikinmaa

In last June-July the news were filled with pictures about Caribbean beaches covered with dead and dying algae. In addition to the beaches, the algae covered the water near them. The large amount of beaching algae has become a yearly problem in 2010’s. Although the aesthetic problems in the beaches (sight and smell) are a major nuisance IMG_20170801_0035.jpgfor areas living on tourism, what happens in coastal waters may be even more alarming for ecosystem health. The decaying algae cause high ammonium and sulphide concentrations in water, and a marked reduction in its oxygen concentration. All these changes are harmful enough to be lethal to large numbers of macrofauna. Especially fish are found dead in large numbers. While the results from last July-August are not yet available, Rodriguez-Martinez et al. have reported the situation in 2018 in Marine Pollution Bulletin 146 (2019) 201–205.

It is probable that this problem is yet another consequence of ongoing climate change. This is an example of effects influencing economies drastically, and the problems are not caused by countries suffering from economic problems. For this reason one needs environmental globalism, the nationalistic populism only worsens the situation. Soon the populist will not have a tourist resort to go to, even if he had saved enough money for it by not accepting the need to do any environmental actions.

Kommentoi kirjoitusta. Avainsanat: climate change, fish mortality, tourism

Aquatic Oil Pollution ? many-sided problem, until oil use is stopped

Torstai 18.7.2019 klo 11.44 - Mikko Nikinmaa


With oil spills, the usual picture in the news is a bird covered with oil. The contaminated bird loses its ability to regulate temperature in water and slowly dies because of heat loss. Although this is a significant problem during oil spills, it is probably not the most important one. As the most important one I would place the effect of oil contamination on mainly unicellular marine algae. Marine algae account for almost half of global photosynthesis, thus being the most important carbon dioxide sinks of the world. Largely because of oil pollution, it has been estimated that the algal carbon dioxide sink has decreased by 20 %. This negative effect is greater than would be caused, if deforestation of Amazon rain forest would increase manyfold. Oil pollution also influences fish. Effects are largely age-dependent and associated mainly with cardiac function. It appears that the toxicity of oil increases with increasing pressure. This is significant, as oil is drilled at deeper depths than earlier. In addition, dispersants, changing oil to small droplets, which are dispersed in the water column, increase the toxicity of oil spill to fish and other aquatic organisms, mostly by increasing the surface area of oil in contact with the (respiratory) surface of organisms. As a consequence, the uptake of toxic components of oil, and thereby their toxic effects, are increased. In contrast, the dispersants in the concentrations used appear to cause little toxicity. It is quite clear that as long as oil is used in significant amounts in fuels and energy production, the problems persist. Further, the socalled biofuels or biodiesels are exactly as bad for aquatic life as fossil oil. Therefore, in terms of combatting climate change, using biofuel is exactly the same as using fossil oil, if the use of fossil fuel is coupled with forestation.

Kommentoi kirjoitusta. Avainsanat: aquatic toxicology, oil spill, water pollution, fish kills

Environmentally friendly diet

Lauantai 3.2.2018 klo 18.04 - Mikko Nikinmaa

When thinking about environmentally friendly dietSirkka.jpg, the need to replace the meat of endothermic animals, cattle, swine, sheep and chicken, by other alternatives is invariably mentioned. This is mainly because the amount of energy (feed) needed to produce a kilogram of meat is high, meaning that large land areas need to be used for animal herding. Also, the need for water is high. As a recent alternative, insect eating has been advocated. The use of ectothermic animals requires only about 1/10 of the energy (and thus feed) in comparison to cattle meat. However, although insect-eating is quite common in some areas, in our society a lot of people have emotional objections to eating insects. Further, the behaviour of chitin - the exoskeleton of insects - in our gut is not really clear yet. Thus, in western societies it is easier to find other sources of ectothermic meat than start using large amounts of insect flesh (although I have no doubt that the use of insects as food will increase in future). Luckily we have already traditionally used the flesh of ectotherms, mainly fish (but also shrimps, mussels, crabs etc.). Increasing fish consumption is just as environmentally friendly as insect eating, provided that the fish are produced in aquaculture and not a result of overfishing. My advocating aquaculture may seem surprising, as aquaculture is thought of causing a large amount of environmental problems. However, this happens with traditional aquaculture, whe fish are cultivated in natural waters, where their feed and faeces eutrophy water, and the use of medicines and parasitecides cause additional problems. Recent advances enable the use of recirculated water, so that future aquaculture can produce fish in the middle of towns, where they are needed. This also removes the need for long-distance transport, which is an environmental problem. Innovative thinking produces innovative solutions to decrease the environmental impacts of food production.

Kommentoi kirjoitusta. Avainsanat: insect eating, fish, aquaculture, meat diet

Rhythmic behaviours are influenced by temperature - significant for climate change responses

Sunnuntai 21.1.2018 klo 15.48 - Mikko Nikinmaa

One significant question with climate change is that although temperature increases, the light-dark cycles at any location remain constant. Many of the responses of animals living in temperate and arctic (antarctic) areas depend on light-dark cycles. If the responses depending on light are affected by temperature, they may occur at inappropriate times in a climate change situation.

This was the outset for our experiments, reported in JM Prokkola et al. (Journal of Experimental Biology, in press). We studied the transcriptional responses of Arctic charr, a polar fish species, acclimated to two temperatures in July-August. Significantly, the rhythmicity of transcription was quite pronounced at an acclimation temperature close to the upper temperatures experienced by the fish in their natural environment. The rhythmicity of transcription all but disappeared at lower acclimation temperature. Since feeding, reproduction, migrations etc. are cued by light rhythms, an effect of temperature on how genes react to light, i.e. temperature effects on circadian rhythms of transcription may affect all those responses negatively. Consequently, effects of climate change can be pronounced even when temperature changes are such that they can easily be tolerated, e.g., by a fish population: any responses normally cued by light rhythm may occur at inappropriate times.

Kommentoi kirjoitusta. Avainsanat: climate change, circadian rhythms, fish survival

State of the world - what has happened in 25 years

Lauantai 18.11.2017 klo 12.40 - Mikko Nikinmaa

Twenty five years ago the Union of Concerned Scientists wrote "World Scientists' Warning to Humanity" (with the major authors and 1700 scientists' signatures) where they were concerned about population growth, freshwater availability, climate change, extinctions etc. Now, scientists have looked at what has happened in the past 25 years, and concluded that "World Scientists' Warning to Humanity: Second Notice" was in order. This article was published on November 13 in Bioscience with William J. Ripple as the first author (in addition to the major authors the article had 15,364 scientist signatories from 184 countries). Apart from the ozone hole, which is now starting to shrink, all the environmental problems recognized in 1992 have become worse, and are still continuing to be more detrimental. For example, the amount of carbon dioxide emissions has increased in the last year after it had stabilized or even slightly decreased in the previous two years. In the past 25 years, the availability of fresh water has decreased by 25 %, mean global temperature increased by 0.5 degrees C, carbon dioxide emissions have almost doubled, the dead zones in marine areas increased by almost a third, forests decreased by about 5 % and vertebrate species number decreased by about 30 %. Although human population growth has stopped in the developed countries, the same thing has not happened in Africa and most Asian countries, whereby the total world population has increased by almost 40 % with no sign of increase rate to be slowing down. The number of extinctions in vertebrates is probably much smaller than that of invertebrates - for example insect biomass in certain protected areas in Germany has decreased by 75 %. A significant problem is also that despite increased catching effort, the marine fish catches have decreased by about 20 % from the best years. One final note of the gloomy statistics, we consider almost always only deforestration as causing a decrease in carbon dioxide removal. However, because of the prevalence of sea area, almost half of global photosynthetic activity takes place in marine algae. Marine pollution has decreased algal photosynthesis by approximately 10 % in the past 25 years.                                

Although most of the indices show radical worsening in the state of global environment, the situation with ozone hole indicates that if mankind heeds the warnings, we are able to make the changes required to keep the environment in satisfactory state. The stratospheric ozone layer above Antarctica is now strongest since 1988. If similar united actions were done for the other questions pinpointed by the authors of the Bioscience article, they could also be solved in reasonable fashion. Changes of diet, schooling, improvement of women's situation, discontinuation of fossil fuel use could all be done if we so decided.

Kommentoi kirjoitusta. Avainsanat: deforestration, population growth, fisheries, climate change, extinctions

Fishing quotas - strict ones are needed to protect fish

Torstai 20.7.2017 klo 13.53 - Mikko Nikinmaa

Fishermen always complain that they are allowed to fish too little and fish biologists have alerted people to the fact that politically decided fishing quotas are too big. If fishing cannot be reduced, several preferred species will become extinct in the next hundred years. The lobbying groups for fishing industry have hitherto been able to convince politicians that putting money in new and effective fishing vessels and having fishing quotas enabling overfishing are good ways of preserving employment - one need not care if preferred fish disappear from nearby areas. With new vessels obtained, e.g. with European Union support, one can have longer fishing journeys than earlier.

It appears that a significant problem with fishing is that the identification of fish by fishermen is poor. If one is approaching the maximum allowed quota for one species, the fish are just marked to be of species, where quotas are not near filling. Giving this type of misinformation varies a lot depending on which country the fisherman is from.

However, even in the interests of fishermen, the fishing quotas should be set on scientific, and not political grounds. Further, the quotas should be followed. And actually, increasing the use of aquacultured fish with land-based feed and effective removal of wastes, is the way forward. All these points are important in order to have fish diversity also for future generations.

Kommentoi kirjoitusta. Avainsanat: fisheries, biodiversity, marine protection

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