Influence of temperature on fish

Water temperature is the most easily observed enviromental factor, and therefore numerous workers have attempted to correlate the behaviour of fish with sea water temperature and its fluctuations. Such changes in oceanic enviroment are, of course, often only concomitant, changes of other factors, such as currents, the direct influence of which may be considerable, while the actual influence of temperature may serve as a most useful indicator of the prevailing and changing ecological condition. Moreover, not only the actual tempertaure, with its range of fluctuation, but its horizontal and vertical gradients, varying from place to place, must be taken into account when using temperature as a direct or indirect ecological indicator. In the following a summaryand an analysis are given of the influence of temperature on the behaviour and survival of fish, with due emphasis upon the use of this information for ascertaining fish concentrations. It is development of hydrographical applications, though it is for obvious reason based mainly upon the result of earlier workers. A summary of the synoptic analyses and forecasting of the ocean thermal structure is given in Chapter 4. 

The sense of  temperature in fish seems to be well developed. Bull (1952) concluded from his careful and extensive experiments that individual telecost perceive and react purposively to a change in water temperature of 0-03 deg celcious. Sullivan (1954) summarized the finding of various workers on the effect of temperature on the movement of fish, and on the influence of temperature on the distribution on fish, and discussed the role of receptor mechanism of the central nervous system in the temperature response. He stated that fish select a certain temperature because of the effect of the same on their movement (activity), and cocluded that the temperature change may act on fish :

1. as a nervous stimulus
2. as a modifier of metabolic processes, and/or
3. as a modifier of bodily activity

In addition it has been shown by Schmidt (1931) and various later workers that the temperature of the environment also has a definite effect on meristic characters of fish : e.g. the numberof vertebrae and of fin-rays increases as the temperature decreases. The effects of temperature of fish manifest themselves in fisheries in a multitude of ways. As temperature affects bodily activity and mobility, low temperature may affect the escape of fish from gear and also the ability of fish to catch mobile food. The temperature may also bring about a difference in the regional distribution of juvenilesand adults, as they often have different temperature tolerance and prferences (Alverson, Pruter, and Rouhoft, 1964). The onshore/offshore movement of demersal fish might also be triggered by temperature. Alverson et al., op.cit., have suggested that the intrusion of colder water into a continental shelf (upewelling) seems to cause shoreward movement of some fish such as Dover sole and Pacific Ocean perch in the N.W. Pacific. Such effect of temperature upon the movement perpendicular to the coast can be demonstrated on only a few species, whereas many other factor, such as the type of bottom, intervene in the corresponding distribution of other species.

Reid (1964) has shown that sardines of genus Engraulis occur in waters of 6 to 22 degrre celcious. Water with this temperature cover about 3/8 ths of the area of the world's ocean; however, Engraullis inhabits less than 1/10 th of the area. Thus it is seen that there are other factors, besides temperature affecting the distribution and, abundance of organism. In addition to direct influence, changes in the temperature may just indicate changes in other environmental factors. 



References
Laevastu T., Hela I. 1970. Fisheries Oceanography: New ocean Enviromental Services. London: Fishing News (Books) Ltd