AGE-RELATED-CHANGES IN SURVIVAL OF LARVAL AND JUVENILE STRIPED BASS IN DIFFERENT CONCENTRATIONS OF CALCIUM AND SODIUM

Survival rates were determined 24 h after striped bass Morone saxatili s from 9 to 78 d old (i.e., days posthatch) were abruptly transferred to water with low or high concentrations of Ca2+ and Na+. These ions a re often added to water containing striped bass to increase survival a fter harvest. Treatment waters contained these ions at the following l evels: (1) low Ca2+ (4 mg/L) and low Na+ (9 mg/L); (2) high Ca2+ (100 mg/L) and low Na+; (3) low Ca2+ and high Na+ (1,780 mg/L): or (4) high Ca2+ and high Na+. Survival was consistently high for fish of all age s in the high Ca2+-high Na+ treatment. However, survival in all other treatments varied depending on fish age. Yolk-sac larvae (9 d posthatc h) had high survival in water with high Na+ and had low survival in wa ter with low Na+; survival of yolk-sac larvae was not related to Ca2concentration. Survival of the youngest postlarvae tested (16 d post-h atch) was remarkably different from that of yolk-sac larvae; the high concentration of Ca2+ reduced mortality and the low Ca2+-high Na+ comb ination was acutely lethal. In both treatments with low Ca2+, there wa s an increase in survival with age of fish older than 16 d. Fish that were 78 d old had 100% survival in all treatments for 24 h, and after 72 h, survival was 97% or higher in all treatments.