Delbert M. Gatlin

Feeding aquaculture in an era of finite resources

Aquacultures pressure on forage fisheries remains hotly contested. This article reviews trends in fishmeal and fish oil use in industrial aquafeeds, showing reduced inclusion rates but greater total use associated with increased aquaculture production and demand for fish high in long-chain omega-3 oils. The ratio of wild fisheries inputs to farmed fish output has fallen to 0.63 for the aquaculture sector as a whole but remains as high as 5.0 for Atlantic salmon. Various plant- and animal-based alternatives are now used or available for industrial aquafeeds, depending on relative prices and consumer acceptance, and the outlook for single-cell organisms to replace fish oil is promising. With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it.

Total sulfur amino acid requirement of juvenile red drum, Sciaenops ocellatus

Two experiments were conducted in a brackish water (6 ± 1 ppt) recirculating system to quantify the total sulfur amino acid requirement of juvenile red drum (Sciaenops ocellatus) and the replacement value of cystine for methionine. The experimental diets contained 35% crude protein from red drum muscle, shrimp meal and crystalline amino acids. Incremental levels of L-methionine were added to the basal diet in the methionine experiment and fed to juvenile red drum for 8 weeks. Based on growth and feed efficiency data, the total sulfur amino acid requirement was determined to be 1.06% of diet (3.03% of dietary protein). In the second experiment to determine the replacement value of cystine for methionine, diets were formulated to contain 0.95% total sulfur amino acids with various eprcentages provided by cystine and methionine. Based on growth and feed efficiency of red drum fed the various diets for 5 weeks, cystine was able to spare approximately 40% of the dietary methionine requirement on an equimolar sulfur basis without significantly reducing performance. Results from these experiments provide information that will assist in formulating diets to satisfy the sulfur amino acid requirement of red drum.

Effects of water temperature and dissolved oxygen on daily feed consumption, feed utilization and growth of channel catfish (Ictalurus punctatus)

Abstract Feed intake (FI), feed efficiency (FE), protein efficiency ratio (PER) and weight gain (WG) of juvenile channel catfish initially weighing 15.0±0.23 g (10–12 cm initial total length) were evaluated under three regimes of time-varying water temperature (mean daily water temperature for Stoneville, MS, USA; mean +3; and, mean −3°C) and three of dissolved oxygen (DO; 100, 70 and 30% air saturation, at each temperature). Two independent experiments lasting 6 and 8 weeks, respectively, simulated spring and fall temperature and photoperiod patterns. Temperature–oxygen regimes were applied to randomly assigned duplicate 110-l aquaria with individual biofilters. Fish were fed once daily, to slight excess, a commercial catfish floating feed. After 45 min, uneaten feed was collected, dried and weighed; then FI was calculated by difference. Fish in each aquarium were weighed collectively, biweekly. In both experiments higher temperatures and higher DO levels produced increased feed consumption. A multivariate regression model was fitted to the data to describe the combined effects of temperature and DO on FI. There was a progressive reduction in FI as DO declined from 100 to 30% air saturation. In both trials weight gain was higher for fish held 3°C above the mean water temperature at 100% air saturation values of DO; whereas, the lowest values of WG were obtained for fish held at 30% air saturation and 3°C below the mean water temperature. Weight gain increased with temperature, with maximum rates reached at 27.1°C with DO equivalent to 100% air saturation. In contrast, when DO was 30% air saturation, growth rates plateaued as ambient temperature exceeded 22.8°C. This model will assist in optimization of feeding practices in channel catfish aquaculture.

Dietary protein requirement of the red drum (Sciaenops ocellatus) and relative use of dietary carbohydrate and lipid

The minimum dietary protein requirement of the red drum (Sciaenops ocellatus) was determined and its ability to utilize dietary lipid and carbohydrate was investigated in terms of growth, feed and protein efficiencies, and body composition. Six semipurified diets were formulated to contain 35, 40 or 45% crude protein from red drum muscle with similar energy: protein ratios. At each protein level, one diet contained 10% lipid while the other contained similar energy but from 3% lipid and additional dextrin. Each diet was fed to juvenile red drum in triplicate aquaria containing brackish (6 ppt) water at 23 ± 2 °C for 8 weeks. Factorial analysis of variance indicated that growth, feed and protein efficiencies were significantly (P < 0.05) affected by protein and lipid/carbohydrate levels. Fish fed diets containing 35% protein or 3% lipid at each protein level had reduced growth and feed efficiency. Highest growth and feed efficiency values were observed for fish fed diets containing 40 and 45% protein and 10% lipid. Enhanced growth and feed efficiency of fish fed diets containing 10% lipid was accompanied by increased lipid deposition in liver and peritoneal cavity. These data indicate that red drum require protein at approximately 40% of dry diet for maximum growth and that they utilize dietary lipid more efficiently than carbohydrate.

Evaluation of brewers yeast (Saccharomyces cerevisiae) as a feed supplement for hybrid striped bass (Morone chrysops×M. saxatilis)

Abstract Two separate feeding trials were conducted to evaluate graded levels of dried brewers yeast in the diet of hybrid striped bass. A basal diet was formulated to contain 40% protein, 10% lipid and an estimated digestible energy level of 3.5 kcal/g. In Trial 1, three incremental levels of dried brewers yeast (1%, 2% and 4% of diet) were added to the basal diet in place of cellulose. In Trial 2, the same levels of brewers yeast were added to the basal diet, but menhaden fish meal and menhaden oil were adjusted to provide isonitrogenous and isolipidic diets. Each diet was fed to three (Trial 1) or four (Trial 2) replicate groups of juvenile hybrid striped bass twice daily at rates approximating apparent satiation for 6 or 8 weeks. After the second feeding trial, a Streptococcus iniae bath challenge was executed to test the effects of diet on disease resistance. Enhanced weight gain and feed efficiency were generally observed in fish fed the diets supplemented with yeast compared to the basal diet in both trials. In the second trial, body composition of whole fish, hemocrit and serum lysozyme levels were observed to be within normal ranges and not influenced by the various dietary treatments. After 9 weeks of feeding in the second trial, exposure to S. iniae resulted in no mortality and reduced signs of disease in fish fed diets supplemented with 2% and 4% brewers yeast, while 20% mortality was observed in fish fed the control diet ( P =0.1). In the second trial, blood neutrophil oxidative radical production, extracellular and intracellular superoxide anion production of head kidney macrophages and serum lysozyme were measured after 16 weeks of feeding each diet. Fish fed the diet with 2% brewers yeast were found to have significantly ( P Based on the result of this study, it is concluded that brewers yeast positively influenced growth performance and feed efficiency of hybrid striped bass as well as resistance to S. iniae infection. In addition, results of immune response assays demonstrate that brewers yeast can be administered for relatively long periods without causing immunosuppression.

Determination of digestibility coefficients of various feedstuffs for red drum (Sciaenops ocellatus)

Abstract The availability of nutrients and energy in feedstuffs to fish may vary considerably, depending on a variety of factors including fish species, ingredient quality and processing conditions. The red drum is an emerging aquaculture species for which information concerning nutrient and energy availability is needed to more precisely formulate diets to meet their requirements and to enable effective substitution of ingredients. This study was conducted with red drum to determine apparent organic matter, protein, lipid, and gross energy digestibility coefficients and apparent phosphorus availability of the following ingredients: select (low temperature) menhaden fish meal; regular-quality menhaden fish meal, poultry by-product meal, meat and bone meal, dehulled soybean meal, cottonseed meal, and wheat. Test diets consisting of a 70:30 mixture of reference diet to test ingredient were utilized with chromic oxide as the non-digestible marker. Organic matter digestibility of ingredients generally decreased as the nitrogen-free extract fraction increased, ranging between 94% for select menhaden fish meal to 47% for wheat. Crude protein digestibility was high for most ingredients, ranging from 77% for regular menhaden fish meal to 97% for wheat, with the exception of poultry by-product meal which was 49%. Lipid digestibility coefficients ranged from 59% for poultry by-product meal to 88% for wheat. Digestible energy coefficients were generally high for the animal meals, ranging from 72% for poultry by-product meal to 95% for select menhaden fish meal however, digestible energy coefficients for plant feedstuffs were considerably lower, from 62% for wheat to 70% for cottonseed meal. Phosphorus availability from animal products was variable, with a low of 27% for poultry by-product meal and a high of 66% for meat and bone meal. Phosphorus availability from soybean meal and cottonseed meal was 47% and 40%, respectively. Wheat had the highest phosphorus availability at 79%. Data from this study indicate red drum can digest and absorb the nutrients in animal products more completely than those from plant products. This difference presumably reflects their inability to effectively digest the nitrogen-free extract portion of plant products. These data provide more precise information concerning nutrient and energy utilization of red drum and will allow ingredient substitutions in practical diet formulations based on levels of available nutrients.

Nutrition and Fish Health

Publisher Summary Proper nutrition has long been recognized as a critical factor in promoting normal growth and sustaining health of fish. Artificial diets manufactured from various feedstuffs are the primary source of nutrition in intensive aquaculture. Prepared diets not only provide the essential nutrients that are required for normal physiological functioning but also may serve as the medium by which fish are exposed to other components, which may affect their health either positively or negatively. A deficiency of any nutrient, if severe enough, can adversely affect fish health either directly, by impairing metabolic functions, or indirectly, by making fish more susceptible to opportunistic disease-causing agents. Arginine, an amino acid, is involved in the synthesis of nitric oxide via nitric oxide synthase, which is inducible in fish. It has been shown to have numerous beneficial effects on T cell-mediated immunity in various animal models and in humans. Some structural carbohydrates associated with the cell walls of yeast and fungi such as β -glucans and mannan oligosaccharides have also shown to enhance the immune response of some fish species. Two promising nonnutritive dietary supplements to potentially aid in disease control of fish are immunostimulants and probiotics. Immunostimulants increase disease resistance by enhancing host defense mechanisms against pathogenic microorganisms, while probiotics decrease the frequency and abundance of pathogenic or opportunistically pathogenic organisms in the environment.

Dietary protein and energy modifications to maximize compensatory growth of channel catfish (Ictalurus punctatus)

A feeding trial was conducted to evaluate influences of dietary protein and energy modifications as well as indispensable amino acid supplementation on channel catfish growth and body composition during compensatory growth. Four diets were formulated to contain 32% or 37% crude protein and were maintained isocaloric at an estimated digestible energy (DE) level of 3.0 or 3.6 kcal/g; a fifth diet was formulated to be equal to the diet containing 32% crude protein and 3.0 kcal DE/g but with the addition of an indispensable amino acid supplement at 5% of diet. Each of the five experimental diets was fed to channel catfish initially weighing 17 g for 6 weeks using either satiate feeding (control) or not feeding for 3 days then feeding to apparent satiation for the next 11 days in three cycles. Weight gain of channel catfish was significantly (P < 0.05) affected by dietary treatment with a dietary energy level of 3.6 kcal DE/g enhancing weight gain. Cumulative weight gain also was increased in fish fed diets containing 37% crude protein compared to those fed diets containing 32% protein or the diet supplemented with amino acids. Compensatory growth was observed in response to the restricted feeding regime. Feed consumption was affected by dietary protein level and feeding regime. Fish fed diets containing amino acid supplementation and 37% protein reduced cumulative feed consumption compared to fish fed the diets with 32% protein. Fish on the restricted feeding regime had reduced feed consumption compared to satiate fed fish. Feed efficiency was improved in fish fed the high-energy diets and those fed the diet with 37% protein. Fish on the restricted feeding regime also had improved cumulative feed efficiency compared to fish fed daily to apparent satiation. Hepatosomatic index at the end of the experiment was altered by feeding regime, while intraperitoneal fat ratio was elevated by feeding higher dietary energy. Composition of liver and muscle was only slightly altered by dietary treatment. Therefore, the restricted feeding regime was capable of inducing elevated growth rates during refeeding but the dietary manipulations did not augment growth rates.

Effects of dietary energy: protein ratio on growth characteristics and body composition of hybrid striped bass, Morone chrysops ♀ X M. saxatilis ♂

Abstract Six semipurified diets with energy: protein (E: P) ratios of 6, 7, 8, 9, 10 and 11 kcal available energy/g protein were fed in triplicate to groups of juvenile hybrid striped bass (initial weight approximately 9.0 g/fish) for a period of 8 weeks in flow-through aquaria receiving fresh well water. The greatest weight gain and protein efficiency ratio values were associated with fish fed diets with E: P ratios ranging from 6 to 9 kcal/g protein. Weight gain was reduced ( P P P P P P P P

Dietary calcium, phytate and zinc interactions in channel catfish

Abstract Interactions among dietary calcium, phytate and zinc were investigated by feeding eight purified egg-white diets containing 0.5 or 2.0% Ca, 0.5 or 1.5% phytate and 20 or 200 mg Zn/kg in a factorial arrangement to triplicate groups of fingerling channel catfish (Ictalurus punctatus) in aquaria for 12 weeks. A significant (P