EFFECTS OF DIETARY-SODIUM CHLORIDE ON RED DRUM JUVENILES IN WATERS OF VARIOUS SALINITIES
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abstract
Three 8-week feeding trials were conducted to determine the effects of supplemental dietary salts on growth and osmoregulation of juvenile red drums (Sciaenops ocellatus) at various water salinities. In each experiment, sodium chloride was added to a basal diet composed of semipurified and practical ingredients; the basal diet provided intrinsic levels of 0.80% Cl, 0.84% K, and 0.92% Na on a dry-matter basis. In fresh water, red drums fed the basal diet supplemented with NaCl at 2% had significantly (P < 0.05) greater weight gain and feed efficiency than fish given the basal diet alone. In brackish water (6%o salinity), fish given the diet supplemented with NaCl at 2% had weight gains that were numerically but not significantly (P = 0.076) greater than gains of fish fed the basal diet. In full-strength artificial seawater (35%o), fish fed diets supplemented with NaCl at 2 and 10% had weight gains not significantly (P = 0.23) different from those of fish fed the basal diet, and those fed the diet supplemented with NaCl at 10% had significantly reduced feed efficiency. None of the salt supplementations significantly affected blood osmolality or total thyroid hormone levels at 4 weeks or the ability of fish maintained in brackish or fresh water to survive transfer to full-strength seawater at 8 weeks. Results from these experiments indicate that dietary supplementation with NaCl improved the growth of red drums in dilute (fresh and brackish) waters, but not in full-strength seawater. Dietary salts for red drums in dilute waters may provide ions that the fish cannot sufficiently extract from hypotonic environments. 1992 Taylor & Francis Group, LLC.
