Temperature 



Brett (25) refers to temperature as a polymorphic environmental factor that 

 may be a lethal agent, a controlling factor regulating metabohsm and 

 development, a limiting factor restricting activity and distribution, a masking 

 factor interacting with other environmental factors, or a directing agent such as 

 a thermal gradient. It appears that the major temperature effect on marine fish 

 larvae is that of a controlling factor regulating metabohc and developmental 

 rates. In turn, those rates can affect survival of larvae through their influence 

 on establishment of exogenous feeding and regulation of food requirements 

 (e.g. 43, 57, 59, 60). For clupeiform, perciform, and pleuronectiform larvae, a 

 6-lO'^C range has been reported in which culture attempts are most successful 

 (8, 10, 43, 57, 59, 61), although some survival can be obtained over wider 

 temperature ranges. 



There are few temperature effect-metaboHc rate studies on marine fish 

 larvae. Laurence (59) examined growth and metabohsm of feeding winter 

 flounder larvae at 2°, 5° and 8°C. Larvae reared at 5° and 8°C were tested 

 until metamorphosis and the specific growth rate at 8*^C (10.1 percent/day) 

 was significantly higher than that at 5°C (5.8 percent/day). The growth rate at 

 2°C (2.6 percent/day) was less than at 5°C but not significantly less. 

 Metamorphosis took 49 days and 80 days at 8° and 5°C, respectively. At 2*^0 

 larvae did not survive more than six weeks after yolk absorption. Power 

 functions describing oxygen consumption of winter flounder in relation to 

 body weight had exponential coefficients lower than the expected theoretical 

 value of 0.80 (0.49 for 8°C, 0.56 for 5°C, 0.54 for 2°C). When separate power 

 functions were fitted for larvae and for metamorphosed juveniles, the 

 exponential coefficients for larvae closely agreed with the theoretical 0.80 

 value for all three temperatures, but the coefficients for metamorphosed 

 juveniles were lower. 



Hoss et al (41) examined the effect of a rapid 12°C rise in temperature 

 (thermal shock) on growth of pinfish Lagodon rhomboides and spot 

 Leiostomus xanthunis, and oxygen consumption of pinfish, to determine if 

 growth and metabohsm could be used to detect sublethal effects of power 

 plant thermal pollution. The fish that they used were transformed juveniles, in 

 most respects (5.15-7.89 mg dry weight for pinfish, 1 1.23-23.70 mg for spot). 

 No significant difference in growth was observed for thermally shocked and 

 control groups. Oxygen consumption rates of experimental and control pinfish 

 indicated that a 12°C shock produced a shght increase in consumption rate 

 which returned to normal levels within a few hours. Their determinations (41) 

 of critical thermal maxima and survival after acute thermal shocks may not 

 represent responses that might be obtained for smaller larvae. 

 Time-temperature exposure histories are critical for determining thermal 



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