FISHERY BULLETIN: VOL. 87, NO. 2. 1989 



black sea bass from just after fertilization through 

 the eighth day of feeding. Results are used to infer 

 differences in early survival and growth capabilities 

 in nature. Particularly important are differences 

 during the first 96 hours of feeding, which probably 

 arise from adaptations necessary for exploiting dif- 

 ferent food supplies. Prey densities tend to be lower 

 in the larval black sea bass's habitat (Theilacker and 

 Dorsey 1980). 



MATERIALS AND METHODS 



The study was conducted with eggs, unfed larvae, 

 and larvae fed for 8 days. The timing of the follow- 

 ing developmental events was noted: hatching (H), 

 completion of eye pigmentation (EP), first feeding 

 (FF), yolk exhaustion (E YS), and death of unfed lar- 

 vae (S). Measurements were made of notochord 

 length (NL), dry weight, % ash, % total carbon, % 

 total nitrogen, % total lipid, energy content, oxy- 

 gen consumption, feeding efficiency, and feeding 

 rate. 



Egg Sources 



Bay anchovy eggs usually (40 collections) were ob- 

 tained 3-5 hours after spawning (before morula 

 stage) by stationary plankton tows in Pivers Island 

 Channel, near Beaufort, NC. For one series of oxy- 

 gen uptake measurements, eggs and milt were ob- 

 tained by stripping ripe adult anchovies. Black sea 

 bass eggs were stripped from six females (313-672 

 g), in which ovulation had been induced by injection 

 of human chorionic gonadotropin, and they were fer- 

 tilized artificially (Tucker 1984). 



Culture Conditions 



Physical conditions for rearing experiments ap- 

 proximated those in natural habitats in North Caro- 

 hna waters during peak spawning. Temperatures 

 were slightly lower than optimal for growth. Bay 

 anchovies were maintained at 24°C and 32°lm with 

 a 14L:10D photoperiod. Black sea bass were main- 

 tained at 20°C and 34%o with a 12L:12D photo- 

 period. Fluorescent lighting provided 1400 lux at the 

 water surface. Incubation and rearing took place in 

 one to eight (usually six) 10 L black cylindrical fiber- 

 glass tanks of filtered seawater. Initial stocking den- 

 sity was 30 or fewer eggs per liter. First-feeding 

 larval density was reduced to fewer than 15/L. Roti- 

 fers, Brachionus plicatilis, of the same strain inves- 

 tigated by Theilacker and McMaster (1971) were 

 added when larval eye pigmentation was complete. 



and densities were maintained at about 20/mL. Phy- 

 toplankton, Chlorella sp. or Nannochloris sp., was 

 also added as food for the rotifers. Nutritional qual- 

 ity of starving rotifers diminishes rapidly. Unless 

 well-fed rotifers are added frequently and all of them 

 are eaten quickly, algae must be present in the rear- 

 ing tanks to maintain their quality. Good rotifer 

 nutrition also ensures that they continue to repro- 

 duce, thus maintaining the full size range. Without 

 algae, rotifers not eaten within several hours be- 

 come empty shells. Without reproduction, a rotifer 

 population tends to consist entirely of large adults. 



Measurements and Calculations 



The times of eye pigmentation and yolk exhaus- 

 tion were determined by microscopic examination. 

 Starvation mortality was determined in the 10 L 

 rearing tanks (5 times for each species, 1-3 tanks). 

 In addition, three starvation mortality determina- 

 tions were made in 2 L dishes using bay anchovy 

 eggs collected on different nights. For each deter- 

 mination, 25 normally developing eggs were placed 

 in each of eight 2 L black glass dishes; dead eggs 

 and larvae were counted and removed periodically, 

 with 100% recovery. 



Egg and larval dry weights were determined 

 directly. Daily samples (usually 30 individuals) were 

 taken randomly from the rearing tanks for deter- 

 mination of dry weight. Each group of specimens 

 was rinsed in distilled water and freeze-dried before 

 weighing. Best-fit regression equations were used 

 to predict dry weight at different ages during devel- 

 opment. Notochord length of 10-52 specimens was 

 measured at key times during development. Instan- 

 taneous, or specific, growth rate was calculated as 

 g = (In W„ - In Wo)IT, in which W„ is the final 

 weight on day n, Wq is the initial weight on day 0, 

 and T is the interval in days. 



I determined energy content of eggs and larvae 

 directly by calorimetry and indirectly by proximate 

 analysis. Eggs and larvae were sampled periodical- 

 ly for ashing, elemental analysis, total lipid assays 

 (black sea bass only), and bomb calorimetry. Ash 

 weights were determined by combustion for 12 

 hours at 500 °C (0.6-2.0 mg subsamples— anchovies: 

 9 samples, 1 or 2 replicates, 12 determinations; black 

 sea bass: 9 samples, 1 or 2 replicates, 17 determina- 

 tions). Total carbon and nitrogen contents were 

 determined with a Carlo-Erba^ model 1106 elemen- 

 tal analyzer (0.5-1.1 mg, usually triplicate, subsam- 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



280 



