water estuaries, and most abundantly in salinities 

 of 20-35%„ (Simmons and Breuer 1962). A wide 

 temperature range of 2°-33° C can be tolerated 

 as long as the temperature change is gradual 

 (Gunter and Hildebrand 1951; Simmons and 

 Breuer 1962). Little is known about the upper and 

 lower limits of temperature and salinity and their 

 effects on survival of eggs and early larval stages, 

 or on early development and growth. 



The objective of this study was to determine the 

 optimum temperatures and salinities for hatching 

 and growth of red drum eggs and larvae. Similar 

 work on temperature and salinity effects on sur- 

 vival and development have been detailed for 

 other marine species (Alderdice and Forrester 

 1971; Alderdice and Velsen 1971; May 1975). 



Methods 



Eggs were obtained from laboratory spawnings 

 induced by manipulations of temperature and 

 photoperiod to simulate natural seasonal changes 

 (Arnold et al. 1977). Brood tank temperatures 

 ranged from 24° to 26° C and salinities from 26 to 

 32"L. The most successful method for rearing 

 larvae under our experimental conditions was the 

 following: 1) Hatching at a density of 50-100 eggs 

 in a 100 ml beaker with 10 ppm erythromycin; 

 2) feeding sequentially the dinoflagellate Proro- 

 centrum micans (500/ml, day 2) and the rotifer 

 Brachionus plicatilis (50-100 /ml, day 3); 3) trans- 

 ferring larvae after 3-4 h feeding on rotifers to a 

 Nitex^ holding chamber in a 1 1 beaker; 4) feeding 

 Artemia salina nauplii to larvae (2 /ml, beginning 

 on day 7). 



Water was changed every fourth day. The hold- 

 ing chambers were made from a cylinder of 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



300 fxm Nitex net glued to a plastic Petri dish; the 

 dish forming the bottom and the Nitex net the 

 sides of the container. Air was introduced into the 

 beaker outside the holding chamber to avoid 

 producing turbulence and bubbles within the 

 chamber. Test salinities were made with filtered 

 seawater (1 /zm) diluted with deionized water or 

 concentrated with artificial sea salts (Instant 

 Ocean). Temperatures were maintained within 

 0.5° C and illumination from fluorescent room 

 lamps was continuous. Percentage hatch, per- 

 centage survival of the larvae to 24 h and 14 d, and 

 standard length (millimeters) of 14-d-old larvae 

 were measured to determine the influence of 

 temperature and salinity. Analyses were con- 

 ducted on the arc sine transformation of the 

 percentages. Two-way factorial analysis of vari- 

 ance was used to test for significant differences 

 among eggs and larvae reared at 12 salinity- 

 temperature conditions. 



Results 



Results of initial tests of the influence of differ- 

 ent temperature-salinity combinations on hatch- 

 ing and survial of red drum showed poor hatching 

 rates at low salinity (101) over all temperatures 

 except 25° C. Red drum eggs floated in 25L 

 or greater salinity and sank to the bottom in lower 

 salinities. High temperatures (30° and 35° C) and 

 high salinities were associated with poor survival 

 of the yolk-sac larvae. Based on these results four 

 salinities (15, 20, 25, and 30D and three tempera- 

 tures (20°, 25°, and 30° C) were used to determine 

 conditions for optimum survival and growth of red 

 drum eggs and larvae. The ranges of salinity and 

 temperature selected are representative of condi- 

 tions occurring in coastal waters during the 

 normal spawning period. 



Table l. — Percentage hatch and larval survival of red drum for each salinity-temperature condition 

 tested. Initially each replicate contained 50-100 eggs. 



570 



