HATCHERY STUDY OF THE EFFECTS OF TEMPERATURE ON EGGS AND YOLKSAC LARVAE OF THE NASSAU GROUPER EPINEPHELUS-STRIATUS

The effects of temperature on eggs and yolksac larvae of the Nassau gr ouper (Epinephelus striatus) were examined under controlled, hatchery conditions. Artificially-fertilized eggs, obtained by induced spawning of captive adults, were stocked (36 eggs per l) into 15 500 l cylindr oconical indoor tanks at temperatures of 26, 28 and 30 degrees C, with five tanks per treatment. A salinity of 37 g l(-1) and a photoperiod of 12 L: 12 D were maintained. Incubation time to hatching was inverse ly related to temperature, decreasing from 24.9 h post-fertilization ( p.f.) at 26 degrees C to 20.4 h p.f. at 30 degrees C, but hatching suc cess (avg. = 82.5%) did not vary with temperature. Survival of pre-fee ding larvae declined more rapidly at the higher temperatures to 91.4, 80.7 and 42.2% by Day 1 p.h, at 26, 28 and 30 degrees C, respectively, indicating that early survival was influenced by factors unrelated to feeding. Development time to the first-feeding stage was inversely re lated to temperature, decreasing from 86 h p.f. (2.54 d p.h.) at 26 de grees C to 71 h p.f. (2.11 d p.h.) at 30 degrees C. Lower temperatures delayed starvation, with survival falling to 32.3, 9.3 and 1.2% by Da y 4 p.h. at 26, 28 and 30 degrees C, respectively. A temperature of 26 degrees C is deemed advantageous to higher temperatures for incubatin g eggs and for rearing first-feeding larvae, although even lower tempe ratures may be feasible. Temperatures within an ecological range can m arkedly influence development rates of E. striatus eggs and yolksac la rvae and hence, dispersal potential, first-feeding and survival in the field.