HOWELL: TEMPERATURE EFFECTS ON YELLOWTAIL FLOUNDER 



ing that several investigators have found a rela- 

 tionship between incubation temperature and 

 yolk utilization efficiency. Laurence (1973) found 

 that overall efficiencies for tautog, Tautoga onitis, 

 were 36.3, 25.5, and 25.89c for 16°, 19°, and 22° C. 

 Ryland and Nichols (1967) found that for plaice, 

 Pleiironectes platessa, efficiencies were roughly 

 35-407r at lower temperatures (2.5°-5.0° C) 

 and 43-579^ at higher temperatures (6.5°-8.5° C). 

 Working with the Atlantic salmon, Salmo salar, 

 Hayes and Pelluet ( 1945) found that efficiency was 

 low (429f ) at temperatures of 0°-5° C, and in- 

 creased linearly with increasing temperature to 

 607^ at 16° C. 



The overall efficiencies in this study, based upon 

 ash-free dry weights, were 43.8, 42.2, and 47.1% 

 for 8°, 10°, and 12° C. The similarity of these values 

 is an indication that within this temperature 

 range, mechanisms are available whereby the in- 

 creased metabolic demands of the larval tissue, 

 caused by the higher temperatures, are balanced 

 by an increased transfer of energy from the yolk 

 for the building of tissues. The fact that increasing 

 growth rate with temperature is accompanied by 

 an increased rate of yolk utilization lends support 

 to this hypothesis. Blaxter and Hempel ( 1966) also 

 point out that overall efficiencies can be similar at 

 different temperatures if the interrelationship be- 

 tween rate of rise in metabolic requirements and 

 reduction in development time are balanced over a 

 temperature range. Wood (1932) reported that 

 yolk utilization efficiency in trout was indepen- 

 dent of temperature between 7° and 12° C. Marr 

 (1966), however, after recalculating the data, con- 

 cluded that efficiency was actually higher at 10° C. 

 Johns and Howell (1980) found that efficiencies 

 were similar in summer flounder, Paralichthys 

 dentatus, larvae at 16° and 21° C. They noted that 

 the ratio of yolk needed for metabolism to yolk 

 converted to tissue remained constant at the two 

 temperatures, causing efficiencies to be similar. 

 Although none of the investigations on yolk utili- 

 zation efficiency demonstrates temperature inde- 

 pendence, several of the studies show, over a par- 

 ticular section of the temperature range tested, 

 that efficiencies are quite similar. These include 

 work on S. salar (Hayes and Pelluet 1945), Clupea 

 harengus (Blaxter and Hempel 1966), and T. onitis 

 (Laurence 1973). 



Larvae incubated at 4° C did not survive to 

 yolk-sac absorption; however, 288 h after hatch- 

 ing, when approximately 2% of the yolk remained, 

 the calculated efficiency was 25.6%. This low 



value indicates that the energy within the yolk 

 was being largely used for metabolic demands 

 other than growth of larval tissue. The relatively 

 low efficiency of yolk conversion at 4° C adds 

 further support to the conclusion that 4° C is a 

 suboptimal temperature for this stock of yellow- 

 tail flounder. 



A reduction in efficiency as development pro- 

 ceeded was noted at all four temperatures. Blaxter 

 and Hempel ( 1966) noted such a decrease in her- 

 ring larvae and concluded that the reduction was 

 due to the relatively higher metabolic demands of 

 heavier larvae. Although no metabolic mea- 

 surements were made in this study, it is suspected 

 that the explanation offered by Blaxter and Hem- 

 pel ( 1966) applies to these results. 



The hypothesis that a deficit in food energy can 

 be caused by yolk exhaustion prior to initiation of 

 exogenous feeding has received considerable at- 

 tention. Such a deficit has been demonstrated by 

 Lasker (1962) for the Pacific sardine, Sardinops 

 caerulea. Laurence (1969, 1973) working with 

 largemouth bass, Micropterus salmoides, and 

 tautog found that no such deficit occurred in 

 either species. Yellowtail flounder larvae reared at 

 8°, 10°, and 12° C in this study, as well as those 

 reared by Smigielski ( 1979), all possessed darkly 

 pigmented eyes, a functional mouth and jaw- ap- 

 paratus, and a completely formed gut at yolk-sac 

 absorption. These morphological traits strongly 

 indicate that larvae were able to begin feeding at 

 this time. Smigielski (1979) further noted that 

 yellowtail flounder larvae were capable of surviv- 

 ing for several days without food after the yolk 

 reserves were depleted. The larva's apparent ca- 

 pacity to feed at yolk-sac absorption, and its ability 

 to survive temporarily without exogenous food 

 make it unlikely that an energy deficit signifi- 

 cantly effects survival. This observation, com- 

 bined with the fact that larvae reared at 8°, 10°, 

 and 12° C were equal in size at yolk-sac absorption, 

 thus conferring equal feeding and predator avoid- 

 ance abilities, is an indication that larvae grow- 

 ing at these temperatures would have equal sur- 

 vival potential. 



Results of this study indicate that yellowtail 

 flounder eggs and yolk-sac larvae are euryther- 

 mal. Smith et al. (1978), studying diel vertical 

 migrations of yellowtail flounder larvae, found 

 that those less than about 4 mm long migrated 

 only short distances, and thus experienced little 

 temperature change. Larger larvae, however, were 

 subjected to as much as a 10° C change (from 5° to 



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