Temperature is important to maintenance of optimum characteristics in water - based ecological systems.

Example- temperatures wich do not kill fish or shellfish may produce effects in metabolism, reproduction and growth as well as reducing certain food organisms.

This will upset balance in the hole system.

Because of complexity of natural systems, it is misleading to generalize on temperature effects on aquatic biota.More proper is to study locally important species.


Temperature directly effects physiology of fish.

Fish approach temperature of surroundings, differing by only 0.5-10ºC.External temperature must be suited to internal temperature needs.Individual species vary in effects.

Rates of metabolism increase with temperature up to lethal limit.Rates vary and are affected by oxygen level and salinity.Rate changes may be indicators for spawning migrations.

Effects on death mechanism:

  1. Accelaration of enzyme reactions may make enzyme inactive
  2. Coagulation of cell proteins
  3. Reduction in permeability of cell membranes
  4. production of toxic products

Temperature range within wich fish reproduce is narrow.Temperature affects embryonic development.Temperature affects occurrence of fish life.Some fish are more tolerant of temperature ranges.

Simultaneous actions may affect fish life(synergistic action).For instance, the effect of NaCN increases with temperature.Temperature and toxicity effects are common.

Decrease in dissolved O2 and rise in metabolism rate may combine to make environment less compatible to fish life.

Acclimation temperatures are important to fish life. Gradual changes are better tolerated than quick changes.

Fish seek out temperature best suited for survival, called "preferred temperature".

Incubation of eggs and development of fry is critically sensitive to temperature.


Physiology, metabolism and development of many species are affected by temperature.

Algae and other aquatic plants:

Increased temperature often eliminates desirable species and helps establish undesirable ones.Is a complicated problem and requires specific study.


In general, growth increases with temperature if food is abundant. not necessarily harmful unless pathogens increase.

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