FISHERY BULLETIN: VOL. 78. NO. 3 



vestigators have found that temperature can 

 affect yolk utilization efficiency and thereby sub- 

 sequent size and feeding ability, the current 

 study examines the hypothesis that temperature 

 affects yolk utilization efficiency and size of yel- 

 lowtail flounder larvae. 



METHODS 



Adult yellowtail flounder were collected south- 

 east of Block Island, R.I., on 28 March 1979 

 aboard a commercial fishing vessel. They were 

 placed in a 680 1 tank periodically supplied with 

 running seawater and transported to the labora- 

 tory where they were held, four to a tank, in 286 1 

 aquaria supplied with a continuous flow of filtered 

 seawater. 



To induce ripening, both sexes were anes- 

 thetized with tricaine methanesulfonate (MS- 

 222^) at a concentration of 1:20,000 g and injected 

 intramuscularly with 2.0 mg of carp pituitary dis- 

 solved in marine fish Ringer's solution per kilo- 

 gram of fish wet weight following Smigielski 

 (1979). Daily injections continued until spawning 

 occurred. Two females of 34.4 and 42.0 cm TL 

 (total length) were anesthetized and their eggs 

 manually stripped into a glass bowl containing 

 0.45 /Ltm filtered, ultraviolet-treated seawater 

 (34.0%o salinity, 10.5° C). The eggs were fertilized 

 with milt stripped from two anesthetized males 

 (34.5 and 33.0 cm TL). The fertilized eggs were 

 divided volumetrically among four 6 1 black plas- 

 tic pans containing seawater identical to that in 

 which fertilization had occurred. Twenty-five 

 lU/ml penicillin and 0.02 mg/ml streptomycin 

 were added to each pan as an antibiotic. These 

 pans were placed in temperature-regulating circu- 

 lation baths, gently aerated, and allowed to 

 equilibrate slowly to the test temperatures. The 

 four test temperatures chosen (4°, 8°, 10°, and 12° 

 C) were maintained at 4.5±0.6°, 8.7±0.6°, 

 10.3±0.5°, and 12.2±0.6° C (mean ± 1 SD). The 

 temperatures chosen encompass the range over 

 which most eggs and larvae of yellowtail flounder 

 have been collected in nature (Royce et al. 1959; 

 Colton 1972; Smith et al. 1975). Dissolved oxygen 

 and salinity ranged from 7.6 to 8.1 mg/1 and 33.0 

 to 34.0%o. Photoperiod was 12D:12L throughout 

 the experiment. 



Measurements of egg and yolk diameters of a 



random sample of unfertilized eggs ( n = 100) were 

 made by ocular micrometer, and egg and yolk vol- 

 umes calculated. 



Prior to weighing, fresh unfertilized eggs were 

 rinsed in three changes of isotonic 0.99f (weight/ 

 volume) ammonium formate to remove residual 

 saltwater. Mean dry weight and ash-free dry 

 weight of 390 eggs were determined to the nearest 

 1.0 ^tg, using a Perkin-Elmer electrobalance fol- 

 lowing the method of Laurence ( 1973). To deter- 

 mine the mean dry weight and ash-free dry weight 

 of yolk per egg it was necessary to subtract mean 

 dry and ash-free dry weight of the egg capsule 

 (zona radiata) from the two values. Twenty-six 

 capsules were removed from embryos just prior to 

 hatching and dry weights and ash-free dry 

 weights were determined by the method previ- 

 ously cited. Mean capsule weights were subtracted 

 from the mean values of dry weight and ash-free 

 dry weight of unfertilized eggs. The difference was 

 taken as the mean dry and ash-free dry weight of 

 yolk per egg. As both mean yolk weight and mean 

 yolk volume were known, it was possible to calcu- 

 late the dry weight and ash-free dry weight of yolk 

 for any given volume. 



Random samples of 25 yolk-sac larvae were re- 

 moved from each temperature treatment begin- 

 ning 2 h after hatching, and continuing at 24-h 

 intervals until the experiments were terminated. 

 Yolk-sac measurements were made with an ocular 

 micrometer. The volume of the elliptical yolk sac 

 ( V^g in cubic millimeters) was calculated from the 

 formula for a spheroid: 



V. 



ys 



(77/6)L//2 



(1) 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



where L is the length (millimeters) and H the 

 height (millimeters) of the yolk sac (Blaxter and 

 Hempel 1963 ). At each sampling period the length 

 from tip of snout to tip of notochord was measured 

 to the nearest 0.01 mm for each of the larvae sam- 

 pled using an ocular micrometer. The fish then 

 were rinsed in ammonium formate, and mean dry 

 weights and ash-free dry weights determined as 

 previously described. 



Because of inherent variability in micromea- 

 surements, data were smoothed using linear re- 

 gression to relate ash-free dry weights of yolk-sac 

 larvae and yolk-sac volumes to numbers of hours 

 posthatch at all four temperatures. Ash-free dry 

 weights of yolk-sac larvae and yolk-sac volumes 

 were predicted using regression equations for each 

 24-h time interval and temperature. Predicted 



732 



