FISHERY BULLETIN: VOL. 78, NO. 3 



larvae at 8° C showing a somewhat lower overall 

 efficiency (32.4^7.). 



Efficiencies calculated at hatching reflect the 

 efficiency with which yolk was converted to larval 

 tissue during embryological development. These 

 values were consistently higher than overall 

 efficiencies (Tables 4-7) and were similar in rank- 

 ing. Based upon ash-free dry weight conversions, 

 larvae at 12° C were most efficient (86.2%), fol- 

 lowed by those at 10° C (76.8%), at 8° C (73.5%), 

 and, last, at 4° C (45.9%). As for overall efficien- 

 cies, caloric efficiencies at hatching were lower 

 than those calculated on an ash-free dry weight 

 basis: 74.7% at 12° C and 54.3% at 8° C. 



A decrease in efficiency with continuing devel- 

 opment was noted at all four temperatures (Tables 

 4-7). 



DISCUSSION 



Mean diameter of eggs used in this study were 

 slightly smaller than mean sizes reported by other 

 investigators (Bigelow and Schroeder 1953; Col- 

 ton and Marak footnote 3). Many variables can 

 effect egg diameter. Laurence (1969) and Alder- 

 dice and Forrester (1974) have demonstrated a 

 relationship between egg diameter and parental 

 size. Egg diameter has also been related to incuba- 

 tion temperature and salinity, as well as time from 

 fertilization (Alderdice and Forrester 1974; Al- 

 derdice et al. 1979). In addition, Blaxter and Hem- 

 pel (1963) found differences in egg diameter be- 

 tween stocks of herring. If any of these variables 

 affect egg size in yellowtail flounder, it appears 

 likely that the results found here may not be com- 

 parable with reported values. 



Larvae incubated at the intermediate tempera- 

 tures (8° and 10° C) were significantly larger at 

 hatching than those incubated at the extremes (4° 

 and 12° C). This conflicts with data of Smigielski^ 

 who found that mean length at hatching was inde- 

 pendent of temperature over a 6°-14° C range. One 

 reason for the different findings may be the time at 

 which measurements were taken. Since hatching 

 occurs over a period of about 12-36 h, depending on 

 the temperature, and since growth is rapid, the 

 mean size estimated will depend on the time mea- 

 surements were taken. Furthermore, Alderdice 

 and Forrester (1974) and Alderdice and Velsen 

 (1971) have shown that larval size at hatching can 



••Alphonse Smigielski, Fisheries Biologist, National Marine 

 Fisheries Service, NOAA, Narragansett, RI 02882, pers. commun. 

 November 1979. 



be different among fish in the same treatment 

 depending on hatching time. 



The implications of larval size at hatching may 

 not be great relative to size at yolk-sac absorption. 

 Upon hatching there is no need for larvae to feed 

 actively due to their endogenous yolk supply. Be- 

 cause larger size confers an advantage in swim- 

 ming ability, which in turn affects feeding ability 

 (Hunter 1972), it follows that the size attained at 

 yolk-sac absorption, when the larvae change to 

 exogenous feeding, is more critical than the size at 

 hatching. Analysis of growth rates from hatching 

 to yolk-sac absorption indicate that larvae at 12° C 

 grew significantly faster than those at other tem- 

 peratures. Because of this, 12° C larvae attained a 

 size equal to that of 8° and 10° C larvae by yolk-sac 

 absorption. Because of the similarity in size' of 

 larvae reared at these three temperatures, it is 

 presumed that they would be equally successful in 

 capturing prey. Although no data were available 

 for 4° C larvae at yolk-sac absorption, their small- 

 er size at hatching, combined with their low con- 

 version efficiency, should result in their being sig- 

 nificantly smaller at yolk-sac absorption. The 

 added fact that all larvae in the 4° C treatment 

 died shortly before yolk-sac absorption makes it 

 probable that 4° C is at, or near, the lower tempera- 

 ture limit for successful reproduction in the south- 

 ern New England yellowtail flounder stock. 



Yolk utilization rate, measured by decrease in 

 yolk-sac volume over time, also was affected sig- 

 nificantly by temperature; the higher the temper- 

 ature, the more rapidly yolk was used. This is to 

 be expected since rate of yolk (food) consumption, 

 is one measure of the rate of physiological func- 

 tions (metabolism and growth) which are tem- 

 perature-dependent in most ectotherms (Brett 

 1970). A number of previous studies have shown 

 similar results (e.g., Blaxter 1956; Ryland and 

 Nichols 1967; Fluchter and Pandian 1968). 



Calculated efficiencies indicate the number of 

 calories incorporated, or the amount of yolk con- 

 verted into larval tissue in a particular time inter- 

 val. The remaining calories, or weight, are lost 

 through the metabolic processes of yolk transfor- 

 mation, maintenance, activity, and excretion. In- 

 cubation temperatures in this study were observed 

 to affect both rate of growth and rate of yolk utili- 

 zation. Since the calculated efficiency will depend 

 on the relationship between these two rates, a 

 change in either rate, relative to the other, will be 

 reflected in a change in efficiency. Because tem- 

 perature affects both these rates, it is not surpris- 



736 



