NOTES 



THE EFFECTS OF PHOTOPERIOD AND 



TEMPERATL'RE ON LABORATORY GROWTH OF 



}V\ ENILES EBASTES DIPLOPROA AND A 



COMPARISON WITH GROWTH IN THE FIELD 



Growth rates of fishes may act as sensitive indi- 

 cators of environmental conditions. Variations in 

 food supply, temperature, photoperiod, and other 

 physical and biotic conditions may be reflected in 

 the pattern of growth in a given species, yet the 

 effect may vary depending upon the ontogenetic 

 stage studied. Young stages, for example, gener- 

 ally tolerate and prefer higher temperatures than 

 adults, both in the laboratory (Ferguson 1958; 

 McCauley and Read 1973) and in the field (Brandt 

 1980 ); thermal optima for growth may similarly be 

 higher. The present study examines the effects of 

 temperature and photoperiod on growth rate in 

 juveniles of the splitnose rockfish, Sebastes dip- 

 loproa, in the laboratory and compares these 

 growth rates with growth in the field. Adults of 

 this species are benthic at depths of 200-500 m in 

 the northeastern Pacific Ocean. Sebastes larvae 

 are pelagic (Ahlstrom 1961), and prejuveniles of 

 this species remain pelagic for about 1 yr, reaching 

 maximum sizes near 55 mm standard length (SL) 

 prior to migrating to the benthic habitat ( Boehlert 

 1977). The thermal regime of the surface waters 

 (13°-22° C) differs greatly from that in the adult 

 habitat (6°-8° C; Reid et al. 1958), suggesting that 

 temperature is an important factor in the life his- 

 tory of this species. 



Materials and Methods 



Prejuveniles were collected from under drifting 

 kelp by dip net 8-18 km offshore from San Diego, 

 Calif (lat. 32°52 ' N, long. 117°20 ' W), and brought 

 to the laboratory. Animals were initially main- 

 tained under ambient temperature and photo- 

 period, but these were changed at 0.5° C and 15 

 min/d, respectively, until reaching the two photo- 

 periods and three temperatures of acclimation (12 

 light:12 dark, 16L:8D; 10°, 15°, and 20° C). Fish for 

 the 12L:12D experiments were collected 17 March 

 1976 at 15.5° C; those for the 16L:8D experiments 

 were collected 14 and 21 May 1976 at 17.7° and 



17.6° C, respectively When acclimation conditions 

 were reached, standard lengths of all fish in each 

 treatment were recorded. During the experiments 

 fish were fed to satiation once daily on a mixture of 

 Trout Chow,' ground squid, and frozen brine 

 shrimp. An average of 26 fish were used for each 

 experiment; the range of initial lengths was 30-55 

 mm SL. 



Individual fish were not marked or tagged; indi- 

 vidual growth rates were estimated by a.ssuming 

 that rank of individuals in length did not change 

 during the experiment. This allowed determina- 

 tion of the size dependence of growth rate, subject 

 to some unmeasured error if rank of individuals 

 changed enough to affect estimated growth rate. 

 These data were fit by photoperiod to quadratic 

 response surface models using stepwise multiple 

 regression (Nie et al. 1975) in the form 



G =a + biLi + biT + bi.Li" + b^^T"" + 6i2L,T 



where G = growth rate (millimeters standard 

 length per day), L, = initial standard length (mil- 

 limeters), T - temperature of acclimation (de- 

 grees Celsius), a = constant, and 6„ = regression 

 coefficients. 



To compare the growth rates measured in the 

 laboratory with growth offish in the field, several 

 specimens were collected for analysis of age using 

 daily growth increments on the otoliths. Fish col- 

 lected for age determination were taken to the 

 laboratory alive where the otoliths were removed 

 and stored dry in vials. Otoliths were processed for 

 age determination as described in Taubert and 

 Coble (1977). Briefly, otoliths (sagittaei were 

 placed on slides with histological mounting 

 medium and ground in sagittal sections. Small 

 otoliths were ground on only one side whereas 

 otoliths from fish >25 mm SL were removed from 

 the slide, remounted, and ground on the other side. 

 After the final grinding cover slips were placed 

 over the otoliths. Each otolith was assigned a ran- 

 dom number and read three times at least a week 

 apart at 800 to 1,000 magnifications. If the range 

 of three independent readings was not within 109f 

 of the mean, the otolith readings were rejected. 



FISHERY BULLETIN; VOL. 79, NO. 4, 1981 



789 



