S.R. Craig

Replacement of fish meal in cobia (Rachycentron canadum) diets using an organically certified protein

n Abstractn n A six-week feeding trial was conducted to evaluate the use of a yeast-based, certified organic protein source as a replacement for fish meal in diets for cobia. Five experimental diets were formulated to provide 40% crude protein and 11% dietary lipid (dry matter basis) with the yeast-based protein source replacing Special Select® menhaden fish meal at 25%, 50%, 75% and 100% of dietary protein. Ten juvenile cobia (initial weight 11.5 g/fish) were randomly stocked in triplicate 300 l circular fiberglass tanks (nn =30 treatment−1) and hand-fed the diets based upon total tank biomass two times daily at 0900 and 1400 h. Fish were group weighed weekly to monitor performance and adjust feeding rations. Water temperature and salinity were maintained at 27 °C and 15‰, respectively.n At the end of the feeding trial, weight gain, ranging from 86% to 512%, and feed conversion ratio values, ranging from 1.9 to 5.8, were significantly affected by the inclusion of the yeast-based protein source, with decreasing values as inclusion levels of the yeast-based protein source rose above 25% of dietary protein. Cobia fed the diet containing 25% of dietary protein from the yeast-based protein source had equal weight gain and feed conversion ratio values as fish fed the control diet composed of 100% fish meal (503 vs. 512 and 1.9 vs. 1.9, respectively). Biological indices including hepatosomatic index, visceral somatic index and muscle ratio were all similarly affected by inclusion of the yeast-based protein source, with significant impacts when inclusion levels rose above 25% of dietary protein. As with the weight gain and feed efficiency ratio values, fish fed the diet containing 25% of protein from the yeast-based source had similar values as those observed in the control animals.n This study represents the first attempt to utilize an organically certified protein source as a replacement for fish meal in diets for juvenile cobia. Although levels of inclusion of the yeast-based protein source above 50% of dietary protein resulted in detrimental effects on production characteristics, the data clearly suggest that, at a minimum, 25% of dietary protein can be provided by this yeast-based protein in diets for cobia.n n

Performance of Advanced Juvenile Cobia, Rachycentron canadum, Reared Under Different Thermal Regimes: Evidence for Compensatory Growth and a Method for Cold Banking

ABSTRACT Two trials were undertaken to examine the growth response of juvenile cobia, Rachycentron canadum, at varying temperatures. The initial trial was conducted to determine the effect of various temperatures (18, 23, and 29°C) on weight gain and feed efficiency. The second trial investigated the effect of elevating water temperature in which fish maintained at 18°C and 23°C to a temperature close to their optimum (29°C). The latter study was undertaken in order to determine the effect of thermal shifts upon subsequent growth response of the species. Such information will assist commercial producers in developing various culture guidelines. As anticipated, differences (P < 0.01) in weight gain were recorded among all treatments, although remarkably, feed efficiency did not differ for cobia held at 23°C and 29°C. Following thermal shift, cobia subjected to the largest temperature change (18–29°C) illustrated an immediate growth response, but specific growth rates (SGR) did not exceed that of cobia held at 29°C for the duration of the trial. Nevertheless, when SGR were examined using fish of similar size (i.e., derived from different time points during the study) evidence for growth compensation was obtained. This study illustrates that cobia can be held at reduced temperatures, without detrimental impact on future performance, as a means of maintaining animals at smaller size for production and experimental purposes: “Cold banking.”

Dietary Protein Requirement of Southern Flounder, Paralichthys lethostigma

Abstract A 12-week feeding trial was conducted to determine the protein requirement of southern flounder, Paralichthys lethostigma. Diets varied crude protein (CP) levels (35, 40, 45, 50, 55, and 60%), while dietary lipid levels were held constant at 14% and dextrin was included to maintain diets isocaloric, with all diets providing 370 kcal available energy/100 g diet. Weight gain (percent of initial weight) ranged from 292-394% and was not significantly affected by dietary protein levels. Feed efficiency ratio values (g gain/g fed) ranged between 0.40-0.54 (P > 0.05). Protein efficiency ratio (g weight gained/g dietary protein fed) did not differ significantly (P > 0.05) between groups (0.9-1.27). The protein requirement was determined by relating percent increase in weight gain with dietary protein levels utilizing two statistical methodologies: least squares regression (protein requirement: 50.3% CP) and a four-parameter logistic growth curve (50.8% CP).

Efficacy of Concentrated Algal Paste During Greenwater Phase of Cobia Larviculture

ABSTRACT The purpose of this study was to determine if concentrated algal paste could effectively replace live algae during the greenwater stage of cobia fingerling production without negative impact upon larval growth or survival. Mean cobia survival per tank from 2 dph through post weaning at 28 dph for the live algae treatment was 24.44 ± 2.43% (mean ± SD) as compared to 24.47 ± 2.48% for the algal paste treatment. Furthermore, the number of fish produced per liter for the live algae treatment was 2.44 ± 0.24 fish/L compared to 2.47 ± 0.25 fish /L recorded from the algal paste treatment. Mean fish weight for cobia weanlings from the live algae treatment was 0.417 ± 0.059 g compared to 0.411 ± 0.026 g for the algal paste treatment. These observations demonstrate that during the greenwater stage of cobia larviculture, live algae can be completely replaced with commercially available, concentrated algal paste without negative impact upon cobia growth, survival, or resultant weanling production per unit volume.

Chemical, Physical and Sensorial Differences in Farmed Southern Flounder (Paralichthys lethostigma) Fed Commercial or Crab Meal-Supplemented Diets

ABSTRACT A 12-week feeding trial was conducted to determine the effects of a commercial and a crab meal-supplemented diet on sensory properties of southern flounder ( Paralichthys lethostigma). Proximate analysis, color, fatty acid composition, texture and sensory analyses were performed on the fillets. A significant difference in flavor was found between fillets fed on a commercial or a crab-meal supplemented diet. No significant difference was found between the fish fillets when comparing fat, protein, fiber content and texture. However, fatty acid composition and color were significantly affected by dietary treatment. The data suggest that crab-meal supplemented finishing diets could be utilized to enhance final product quality.