FISHERY BULLETIN: VOL. 75, NO. 3 



MATERIALS AND METHODS 



Adult winter flounder were captured by trawl 

 net from Narragansett Bay, R.I., and maintained 

 in 1,900-liter experimental aquaria. Embryos 

 were obtained by allowing the fish to ripen nat- 

 urally under optimum temperature and photo- 

 period conditions or causing ovulation with 

 hormones according to the techniques of Smigiel- 

 ski (1975). Embryos were incubated with methods 

 developed at the Narragansett Laboratory (Smi- 

 gielski and Arnold 1972). 



All experiments and rearing were done at 8°C 

 during these studies since this temperature is the 

 approximate mean temperature for the entire per- 

 iod from hatching to metamorphosis for winter 

 flounder in the Narragansett Bay area. Stock cul- 

 tures of larvae were reared in series of black 64- 

 liter experimental aquaria. The aquaria were 

 placed in an environmental room or in water 

 baths where the temperatures were maintained 

 by program recorders controlling heating and 

 cooling coils. All experimental aquaria were aer- 

 ated with air stones and were semiclosed systems 

 with a portion of the seawater being replenished 

 every 1 or 2 days. Illumination was controlled by 

 timers which provided a 12:12 day-night photo- 

 period corresponding to the mean photoperiod 

 during the normal winter flounder spawning 

 time. 



Zooplankton fed during all experiments consist- 

 ed mainly of the nauplii, copepodites, and adults 

 of the copepods Acartia clausi, Centropages hama- 

 tus, and a few Temora longicornis and Euryte mora 

 affinis collected from the Narragansett Bay area 

 with 0.5-m plankton nets fitted with 64- and 116- 

 )u.m mesh. Collections were sieved through 200- or 

 500-yu.m mesh strainers, depending on the size of 

 larvae to be fed. Plankton densities in experi- 

 mental aquaria were monitored by taking two to 

 four 5-ml aliquots from the aquaria and counting 

 the number of plankters under a dissecting 

 microscope. 



The relationship between larval size (body dry 

 weight) and stomach contents was studied from 

 hatching to metamorphosis. Larvae were reared 

 in a 64-liter black aquarium and were fed high 

 prey concentrations of 13.6-20.5 cal/liter or ap- 

 proximately 2 or 3 nauplii/ml. Samples of 25 

 larvae were taken each week until metamor- 

 phosis for stomach analyses and dry body weight 

 determinations. 



Experiments determining the influence of prey 



concentration on daily feeding intensity expressed 

 as stomach contents were conducted at 0.68, 3.41, 

 6.80, 20.5, 34.1, and 47.8 cal/liter (corresponding 

 to 0.1, 0.5, 1.0, 3.0, 5.0, and 7.0 nauplii/ml). Larvae 

 aged 2, 5, and 7 wk after hatching were used. 

 Approximately 25 larvae were placed in all black 

 4-liter aquaria containing the desired prey densi- 

 ties. The larvae were allowed to feed for 1 day's 

 photoperiod (12 h) after which they were pipetted 

 onto a 100-/u.m mesh screen and allowed to suffo- 

 cate to prevent regurgitation of food before being 

 preserved in 5% Formalin. 2 Ten larvae from each 

 prey concentration were used for stomach analy- 

 ses and 10 were used for mean dry body weight 

 determinations. Stomach analyses were done 

 with a dissecting microscope. Larval stomachs 

 and intestines were teased apart with fine needles, 

 and contents were identified to genus and species 

 if possible. 



Digestion rate measured by gut clearance time 

 of larval winter flounder at 8°C was determined 

 by feeding dyed zooplankton according to the tech- 

 niques of Laurence (1971a). Transparency of the 

 larvae permitted visual observation of dyed 

 plankters in stomachs of living larvae. To deter- 

 mine the evacuation time of the stomach and 

 intestine under active feeding conditions, larvae 

 feeding on dyed plankters at concentrations of 

 1 or 2 nauplii/ml were removed and placed in 

 duplicate aquaria with similar concentrations of 

 nondyed plankton, and the gut clearance times of 

 the dyed plankters from individual larvae were 

 recorded. 



Experiments determining the influence of tem- 

 perature on growth of winter flounder larvae were 

 conducted in 38-liter experimental aquaria. Feed- 

 ing, monitoring, and sampling techniques and 

 results for these experiments are described in 

 detail by Laurence (1975). 



The influence of planktonic prey concentration 

 on growth and survival at 8°C from the period 

 hatching to metamorphosis was studied at prey 

 concentrations of 0.068, 0.68, 3.41, 6.80, and 20.5 

 cal/liter, corresponding approximately to 0.01, 

 0.1, 0.5, 1.0, and 3.0 nauplii/ml. Larvae were 

 stocked at an initial density of 500 per aquarium; 

 methods for maintaining prey concentrations, 

 sampling, and determining growth and survival 

 rates are described in detail by Laurence (1974). 



Standard manometer equipment (Warburg res- 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



530 



