66 



Fishery Bulletin 91(1), 1993 



Furthermore, physiological changes as well as the 

 change in food source might also register on the 

 otolith. 



This study is the first in a continuing sequence of 

 investigations on the effects of environment and physi- 

 ology on the formation of subannual increments in win- 

 ter flounder otoliths. Relationships between behavioral 

 and anatomical changes were defined and correlated 

 with baseline data on daily growth increments. Growth 

 rates of both wild and laboratory-reared larvae were 

 determined. Increment counts and morphological 

 changes from known-age laboratory-reared fish were 

 compared with those of wild fish to establish anatomi- 

 cal markers in the otolith during the first year. 



Materials and methods 



Acquisition of eggs and larval rearing 



Adults caught in Narragansett Bay served as gamete 

 sources. Eggs fertilized in the laboratory were acquired 

 from the National Marine Fisheries Service (NMFS) 

 and Environmental Protection Agency (EPA) laborato- 

 ries at Narragansett, Rhode Island during February 

 and March 1981. Larvae hatched 15 March 1981 

 (termed the Mar 15 group) were reared in static trays 

 using methods of Klein-MacPhee et al. (1980). The light 

 cycle was maintained at 11:13 (light/dark). Light in- 

 tensity in the growth trays varied between 256 and 

 1777 lux. A separate 114 L tank was maintained for 

 behavioral observations. Light intensity in this tank 

 was 847-4780 lux. Salinity range was 32-33 %,, tem- 

 perature was kept at 5-10° C (±1°C) without diel varia- 

 tion until July, when temperature was allowed to 

 roughly follow seasonal patterns (Fig. 1). Larvae were 

 fed once daily unicellular green algae Tetraselmis 

 souscii and rotifers Brachionus sp., beginning at 3-5 d 

 before yolksac absorption began. Rotifer concentrations 

 of at least 1/mL were maintained, although concentra- 

 tions ranged to over 20/mL. When larvae were 40 d 

 old, newly-hatched brine shrimp were added to main- 

 tain prey concentrations of 1/mL. After several months, 

 fish were fed frozen brine shrimp with the addition of 

 chopped mussels at irregular intervals. 



Heavy mortalities (>90%) reduced larval populations 

 such that only 30 fish survived through metamorpho- 

 sis ( 40-60 d posthatch). Of the metamorphosed fish, 11 

 lived 1 yr and then were killed for otolith examination. 

 Due to physiological effects induced by natural mor- 

 tality, only otoliths from sacrificed fish were examined. 



Sampling 



Initially, 10 fish per day selected at random were re- 

 moved and preserved in 95% ethanol. After hatching, 



i 'i '< '1 'i '1 '1 '1 '1 '1 ', '1 ', ', ', ', 



>981 1982 



Figure 1 



Water temperatures showing mean and range of bimonthly 

 temperatures. Arrows represent hatch-group dates (day of 

 50% hatch) of winter flounder Pleuronectes americanus. 



fish were sampled at 1-6 d intervals until metamor- 

 phosis. In an effort to conserve the 30 fish surviving 

 metamorphosis, additional samples of laboratory-reared 

 larvae in 95% ethanol were provided for ageing by the 

 NMFS Narragansett Laboratory (hereafter referred to 

 as the LR hatch group). These samples were of larvae 

 0-55 d old and were reared using the same methods as 

 the Mar 15 hatch group. 



Standard length measurements were obtained from 

 preserved fish. To check for shrinkage in body length, 

 larvae were measured before and after 1 week's pres- 

 ervation and percent shrinkage determined. 



Collections 



Wild young-of-the-year (YOY) winter flounder were col- 

 lected throughout summer 1981 using beach seines 

 from estuaries along Cape Cod. Otoliths were dissected 

 from these specimens. 



Otolith preparation and analyses 



Body lengths of preserved larvae were measured on 

 glass slides. In larvae (hatch to -30 d), sagittae could 

 not be distinguished from the asterisci or lapilli; there- 

 fore all otolith pairs were removed and aged. In fish 



