I am the specialist for river's fish and fishing my dear @Abhijit! I do agree that high temperature causes negative impact on enzymes, definitely yes!

Increased oceanic volume and concomitant sea level rise have tremendous implications for coastal environments. Sea levels have risen (0.1-0.3 m over the past century) in conjunction with the rising global temperature, but with a time lag of 19 years. Depending on model factors, predicted increases range from 0.3 to 5.0 m, possibly inundating almost 1 million km2 of coastal land

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=33&ved=0CCoQFjACOB4&url=http%3A%2F%2Fassets.panda.org%2Fdownloads%2Fccandmarinefisheriesreport.doc&ei=jFl4VMnqJeqM7AbunYHoCw&usg=AFQjCNE3aT0b-7I-cUoGxD4cjeriukBOkw&cad=rja

Dear Prof, as you say, high temperature causes negative impact on enzymes.  One consequence will be that the content of unsaturated fatty acids that are good for health, are a lot less in fishes from seas where the temperature is high.  Omega fatty acids are perhaps double in fish from cold waters like salmon, as compared to our mackerel from warmer seas.

'Cold-water varieties of fish like mackerel, tuna, salmon, sardines and herring contain high amounts of omega-3 fatty acids.'

http://my.clevelandclinic.org/services/heart/prevention/nutrition/food-choices/omega-3-fatty-acids

I am the specialist for river's fish and fishing my dear @Abhijit! I do agree that high temperature causes negative impact on enzymes, definitely yes!

A few more facts on increased ocean temperature on marine fish.  Let me re-phrase:

Rising ocean temperatures due to climate change is modifying fish distribution and the productivity of marine and freshwater species. This affects the sustainability of fisheries and aquaculture, and the livelihoods of the communities that depend on fisheries.  The effect of sea level rise means that coastal fishing communities are in the front line of climate change.  Inland fishing (rivers, lakes) is affected by changing rainfall patterns and water use.

The active sites of enzymes get disintegrated due to rise in temperature. Hence, enzymes working inside the body of fishes get damaged. It adversely affect the physiological processes of fishes.

High temperature, that is lethal to fish species, determines the distribution and abundance of it’s populations.Many substances (like  cyanide, phenolic compounds etc.) exhibit increased toxicity at elevated temperatures.

Apart from the organism survival, the growth and reproduction of fishes also have critical temperature ranges. If the temperature of ambient water get increased beyond that level, the species of fish will just die.

Dear All,

I think answering this question needs the knowledge of a fish biologist and ecologist. I am entomologist, I know so much that the increase of water temperature depending on the intensity of increase and the fishes’ tolerance to temperature may cause not only physiological changes but also the change of sea ecosystems. Even characteristics of marine bioms can be heavily influenced. The situation is dangerous because of other harms: increasing pollution (oil, chemicals etc.) and the overfishing of seas and oceans.

Rising temperature might be the cause!

Besides the specialists answers of my dear friend @Ljubomir, I add the following contribution about "Climate change impacts on the marine environment": 

Climate change is affecting ocean temperatures, the supply of nutrients, ocean chemistry, food chains, wind systems, ocean currents and extreme events such as cyclones. All of these, in turn, affect the distribution, abundance, breeding cycles and migrations of marine plants and animals that millions of people rely on for food and income.

Evidence is emerging that marine organisms may be responding faster to climate change than land-based plants and animals. As the climate warms, marine plants and animals are shifting towards the poles changing marine food webs and impacting the plants, and animals (including people) that depend on them. The slower ocean dynamics also means that some changes, such as ocean acidification, will be irreversible this century. The full report is on the following page:

http://www.wwf.org.au/our_work/saving_the_natural_world/oceans_and_marine/marine_threats/climate_change_impacts/

This is a photo of many fishes dead because of warming in Serbian river Timok, three years ago!

http://www.vesti.rs/Drustvo/Riba-uginula-od-vrucine.html

The following link by Union of Concerned Scientists about climate hot map in global warming effects on lakes and rivers discusses this issue in terms of Displacement of cold-water species, Dead zones,  Stress., and Disease. See the whole repoprt on the web page:

http://www.climatehotmap.org/global-warming-effects/lakes-and-rivers.html

Friends, we have to apply our science when we carry out our daily activities, and think of the CO2, the methane and other gases that cause global warming, and climate change.  Will being thoughtful make us crazy?  We are borrowing our earth from the future generation.  We also need to conserve and preserve resources like food and water, as we have been expressing on this thread.  

https://www.researchgate.net/post/Is_there_any_viable_and_innovative_solution_for_the_worlds_food_crisis_and_food-shortage_problems#5479937bcf57d7d32f8b4570