An Early Larval Feeding Protocol and Hypersaline Acclimation of Larval Spotted Seatrout

Abstract

The availability of Spotted Seatrout Cynoscion nebulosus to anglers along the Texas coast is supported by a stock enhancement program that is managed by the Texas Parks and Wildlife Department. A study was conducted to improve production protocols during frequent hypersaline conditions in rearing ponds. The objectives of the study were to (1) develop a feeding protocol for use during extended indoor larval rearing and (2) determine whether gradual hypersaline acclimation during extended indoor larval rearing leads to increased growth and survival of Spotted Seatrout larvae when they are subjected to hypersaline conditions. Two feeding trials were conducted to evaluate four rotifer enrichments (Algamac-3050, Easy Dry Selco, Ori-One, and Rotigrow Plus) that are used in a standard larval Spotted Seatrout diet. The feeding trials were necessary to ensure larvae health and survival for the salinity acclimation trial. The larvae in both trials that were fed with Algamac-3050-enriched rotifers exhibited significantly greater (P < 0.05) survival and growth (i.e., length, weight, specific growth rate, and percent weight gain). Based on these results, Algamac-3050 was used in a subsequent salinity acclimation trial. In the salinity acclimation trial, 3-dposthatch (dph) larvae at 35‰ were subjected to increased salinity at a rate of 1‰/d; then at 3, 6, 9, and 12 dph, they were subjected to a hypersaline (50‰) condition to simulate pond stocking. The percentage of survival was highest when the larvae were acclimated until 6 or 9 dph (52.5 ± 7.0% and 65.0 ± 7.7% [mean ± SD], respectively) with no improvement in acclimation to 12 dph (65.2 ± 7.1%). The results for growth and percentage survival displayed similar trends. This study indicates that rearing larval Spotted Seatrout in hypersaline conditions is improved by increasing the indoor rearing time beyond 3 dph and gradually acclimating the larvae to a higher salinity during an extended rearing time.