Ewen McLean

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

Abstract 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 (n =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. 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. 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.

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).

Effect of Growth Hormone and Salbutamol on Growth Performance, Fillet Proximate Composition and Pigmentation of Rainbow Trout (Oncorhynchus mykiss).

Growth hormone (GH) and salbutamol were employed to manipulate protein and lipid turnover in rainbow trout. The effect of these treatments upon growth and their impact upon pigmentation, proximate composition and production yield was examined. The experiment was conducted in two steps: a 6-week restricted feeding experiment with 336 fish (mean weight 461 g, S.D.=61 g) in 16 tanks, followed by a 4-week satiation feeding experiment with 224 fish (range 400–600 g). GH (dose 5 mg kg−1 body weight, bi-weekly, i.p.-injected) and salbutamol (dose 5 mg kg−1 feed) were randomly assigned in a 2×2 factorial with four replicates, each of which consisted of diets containing either 0 mg astaxanthin, 16.7 mg astaxanthin, 33.3 mg astaxanthin or 50 mg astaxanthin/kg feed. Feed consumption was measured daily and weight and length measured bi-weekly. Mean length was greater (P=0.005) in GH-treated animals (36.7 vs. 36.3 cm, S.E.M.=0.8 cm) at the end of the restricted feeding experiment, whereas both mean length and weight were greater (P<0.0005) at the end of the satiation feeding experiment (39.9 vs. 39.2 cm, S.E.M.=0.8 cm, and 975 vs. 930 g, S.E.M.=6 g). Salbutamol modified fish growth patterns but not end length and weight. Feed conversion ratios (FCR) were lower (P=0.044 and P=0.0003, respectively) for GH-treated fish after restricted (GH: 0.84 and GH+salbutamol 0.82 vs. control: 0.86 and salbutamol: 0.85; S.D.=0.028) and satiation feeding phases (GH: 0.89 and GH+salbutamol 0.94 vs. control: 1.00 and salbutamol: 1.01; S.D.=0.039). Although no overall effect of salbutamol treatment was seen, the FCR for salbutamol-treated fish improved during the restricted feeding phase, resulting in lower (P=0.03) FCR during the third bi-weekly period of this phase (salbutamol: 0.90 and GH+salbutamol: 0.86 vs. control: 0.95 and GH: 0.94; S.E.M.: 0.014). GH treatment reduced fillet pigmentation. This effect was most pronounced in fish receiving 16.7 mg astaxanthin/kg feed (1.91 vs. 2.33 mg astaxanthin-equivalents kg−1 fish, S.D.=0.35, P=0.0037), less when fed 33.3 mg/kg feed (3.13 vs. 3.65 mg astaxanthin-equivalents kg−1 fish, S.D.=0.50, P=0.012), but was without effect on fish fed 50 mg/kg feed (3.94 vs. 4.48, S.D.=1.16, P=0.25). Neither GH nor salbutamol affected visceral-somatic index (VSI), proximate composition or fillet colour.

Designing Fish for Improved Human Health Status

The time-course of accumulation of dietary organic and inorganic selenium (Se; 1.5 mg Se kg−1 dry weight feed) was examined for muscle and hepatic tissues of hybrid striped bass (HSB) over 6 weeks. Animals, which had been fed a Se deficient diet for 2 months prior to study, were maintained in a recirculating life support system at 28 ± 1°C. PIT tagged fish were randomly assigned to one of 24 120 L aquaria (n = 5 per tank) and subsequently fed one of four diets: a fishmeal-based diet (control), soybean-casein-based feeds either supplemented with organic (SelPlex®) or inorganic (sodium selenite) Se or as a basal diet, purposefully deficient in Se. Fish were fed twice daily on a 4% body weight basis. Samples taken at trial start (week 0), mid-way (3 weeks) and at trial end (6 weeks) included weight and length data, hepatosomatic (HSI) and visceral (VSI) indices, intraperitoneal fat (IPF) and muscle (MR) and feed conversion (FCR) ratios, serum protein (SP), hematocrit (PCV), and serum glutathione peroxidase (GPx) activity and muscle and heaptic Se concentrations. Survival was also monitored throughout the study. Muscle and hepatic Se levels increased in fishmeal and Se supplemented diets throughout the study. At trail end, greatest weight gain (P < 0.05) was observed in fish fed the control, fishmeal-based diet. Comparison of tissue Se levels indicated that the liver accumulated this mineral at greater concentrations than the muscle with highest levels being observed in the inorganic Se fed fish (P < 0.05). Se accumulation in control and inorganic Se fed fish was similar, whilst Se in the liver of fish fed the Se deficient diet was lowest among groups (P < 0.05). Muscle Se accumulation was found to be greatest in organic Se containing diets (P < 0.05), whereas the basal, Se deficient diet group, returned lowest levels (P < 0.05). Plasma GPx activity was similar in HSB fed the fishmeal and organic Se diets. The fishmeal fed group expressed higher (P < 0.05) GPx levels than that recorded for either the inorganic or basal diets. At trial end, no differences were recorded between groups for PCV or HSI, VSI or IPF. SP levels and MR were higher (P < 0.05) in fishmeal control fed fish. FCRs were lowest in fishmeal fed fish and highest for the Se deficient or basal diet. These studies demonstrate the feasibility of producing cultured fish with heightened levels of Se using simple dietary manipulations for 4–6 weeks or less before harvesting.

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.

B.A. Costa-Pierce, A. Desbonnet, P. Edwardsand D. Baker (eds) Urban Aquaculture

A first look of this book’s cover suggested a fishing-orientation, with large squid and commercial boats being in prominence. The title better reflected content however—which centres attention upon the production and holding of aquatic organisms in and close to conurbations. This brought to mind some fairly unsavoury images of aquaculture ponds viewed in the environs of various metropolises in China, the Indian sub-continent, and throughout Southeast Asia. But this will be considered later. Let’s get rid of some generalities: overall, the production quality of this text is high with excellent standardization of formatting and good reproduction of figures, diagrams and photographic images. The text contains 19 chapters divided into five areas: Introductory (comprising 8% of total), Asia (33%), Europe (6%) and North America (20%), Education and outreach (25%), and Synthesis (3.5%). The Preface,