Ronald W. Hardy

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.

Apparent protein digestibility and mineral availabilities in various feed ingredients for salmonid feeds

Apparent digestibility of protein and availability of minerals (Ca, K, P, Mg, Na, Cu, Fe, Mn, Sr, Zn) in various feed ingredients were determined for coho salmon and rainbow trout using yttrium oxide (Y2O3) as the inert marker and passive feces collection tanks. The feed ingredients were herring meal, menhaden meal, anchovy meal, deboned whitefish meal, poultry by-product meal, feather meal, soybean meal, corn gluten meal, wheat gluten meal, wheat middling and wheat flour. Apparent digestibility (%) of protein and availability (%) of minerals were determined as a fractional net absorption of nutrients from diets. Apparent digestibility of protein and availability of K was high (>80%) in all feed ingredients, whereas digestibility of dry matter and availability of Ca, Cu, Fe, Mg, Mn, Na, P, Sr and Zn were variable among ingredients. Apparent availability (%) of mineral elements was not significantly correlated to the amount of nutrient intake (μg nutrient g−1 BW day−1) in any test diet. Net nutrient absorption (μg g−1 BW day−1) was positively correlated (P<0.05) to the nutrient intake except for Mn, Fe and Ca. Fecal nutrient losses (μg g−1 BW day−1) were positively correlated (P<0.05) to nutrient intake except for protein, Na, K and Zn.

Status and opportunities for genomics research with rainbow trout

The rainbow trout (Oncorhynchus mykiss) is one of the most widely studied of model fish species. Extensive basic biological information has been collected for this species, which because of their large size relative to other model fish species are particularly suitable for studies requiring ample quantities of specific cells and tissue types. Rainbow trout have been widely utilized for research in carcinogenesis, toxicology, comparative immunology, disease ecology, physiology and nutrition. They are distinctive in having evolved from a relatively recent tetraploid event, resulting in a high incidence of duplicated genes. Natural populations are available and have been well characterized for chromosomal, protein, molecular and quantitative genetic variation. Their ease of culture, and experimental and aquacultural significance has led to the development of clonal lines and the widespread application of transgenic technology to this species. Numerous microsatellites have been isolated and two relatively detailed genetic maps have been developed. Extensive sequencing of expressed sequence tags has begun and four BAC libraries have been developed. The development and analysis of additional genomic sequence data will provide distinctive opportunities to address problems in areas such as evolution of the immune system and duplicate genes.

Alternate protein sources for salmon and trout diets

Abstract Growth of aquaculture throughout the world requires increased production of fish feeds. Increased production of fish feed will require increased quantities of feed ingredients, mainly protein sources. Most high-value species of fish raised by aquaculture are carnivores requiring feeds containing 400 g kg−1 or more protein, generally supplied by fish meal. World fish meal production is not expected to increase beyond current levels. This has stimulated research into alternatives to fish meal to supply protein in fish feeds, such as animal and fish processing by-product meals, oilseed proteins and concentrates, and protein concentrates produced from grains. Most alternate protein sources have one or more negative attributes that limit their use in fish feeds. One major concern is how the use of alternate protein sources affect the content of fish farm effluent water. Innovative research on reducing or mitigating the negative qualities of alternate protein sources is increasing the potential for their use in fish feeds and will help alleviate future demands for fish meal by the aquaculture industry.

Rainbow Trout, Oncorhynchus mykiss

Rainbow trout are classified as Oncorhynchus mykiss, and as such belong to the same genus as Pacific salmon, and to the family Salmonidae, which includes Atlantic salmon (Salmo salar), various trout (Salvelinus sp.), Arctic char (Salvelinus alpinus), Arctic grayling (Thymallus arcticus) and whitefish (Coregonus sp.). Rainbow trout are native to areas around the North Pacific Ocean, from southern California through Alaska, the Aleutians and the western Pacific areas of the Kamchatka Peninsula and Okhotska Sea drainages. Rainbow trout primarily inhabit fresh water, but in the eastern and western North Pacific anadromous stocks are found. These stocks follow a life cycle similar to that of Pacific salmon, in that they spend a part of their life in the ocean, but return to lakes and rivers for spawning and the fry and juvenile stages of their life history. Most strains of rainbow trout can adapt to life in sea water, once they reach the post-juvenile stage (c. 75–100 g), through a gradual increase in salinity of their rearing water. This is one of the qualities of rainbow trout that has led to their prominence as a farmed species of fish. Rainbow trout have been cultured for hundreds of years, and are the most widely farmed trout in the world. Rainbow trout can tolerate a wide range of water temperatures and other environmental variables, such as water quality, but they require highly oxygenated water and thrive in water temperatures of 13–18°C. They are a highly valued foodfish, and can be grown to have pigmented (red) or non-pigmented (white) flesh, depending upon their diet. In North America, Britain, Denmark, France and Italy, most trout farming occurs in fresh water, using flow-through water-supply systems. In Chile and Scandinavian countries, rainbow trout are grown in marine cages after an initial phase in fresh water. Diet formulations for rainbow trout grown in marine cages differ somewhat from those for trout grown in fresh water (Table 14.1). Global production of rainbow trout was 358,456 t in 1995, second only to Atlantic salmon among salmonids (Tacon, 1998). France, Chile, Denmark and Italy

Replacement of herring oil with menhaden oil, soybean oil, or tallow in the diets of Atlantic salmon raised in marine net-pens

Abstract Groups of Atlantic salmon held in marine net-pens were fed Oregon Moist Pellets in which herring oil was replaced with either menhaden oil, soybean oil, or tallow. The lipid sources constituted approximately 37% of the total lipid in the diet, the remainder being contributed by the other dietary ingredients. After 23 weeks of feeding, the fish were harvested and growth, chemical composition, and sensory attributes were measured. Dietary lipid source did not affect growth or proximate composition of the fillets. Fatty acid composition of the fillets reflected the fatty acid composition of the diets, although the differences in fatty acid composition among groups of fish were less than the differences in fatty acid composition among the experimental diets. Sensory attributes were not affected by dietary lipid source. This study shows that Atlantic salmon can utilize alternate lipid sources in the diet without compromising growth or organoleptic quality and that dietary lipid substitution offers the possibility of producing fish containing fatty acid profiles preferred in the market.

Effects of lysine supplementation in plant protein-based diets on the performance of rainbow trout (Oncorhynchus mykiss) and apparent digestibility coefficients of nutrients

Abstract Feeds for carnivorous fish contain large proportions of fish meal. Increasing amounts of plant protein meals must be formulated into fish feeds since fish meal production is not growing worldwide. However, relative to fish meal, many plant protein meals are deficient in lysine. In this experiment, seven diets were made such that the reference diet (Diet 1) contained 32.1% fish meal, 46% crude protein (CP) and 2.25% lysine. The basal diet (Diet 2) had 15% fish meal, 43% CP and 1.5% lysine. Diets 3–7 contained 15% fish meal, 43% CP and 1.65, 1.8, 1.95, 2.1 and 2.25% lysine, respectively. Diets 2–7 were isonitrogenous and all diets were isocaloric. One thousand and fifty rainbow trout (initial body weight 14.9±0.4 g) were randomly assigned to twenty-one 150-l fiberglass tanks with 50 fish per tank, and three tanks per dietary treatment. After an 8-week growth period, weight gains were 82.7, 57.9, 61.7, 73.2, 74.5, 72.8, 71.8 g for fish fed Diets 1–7, respectively. Feed conversion ratios were 0.99, 1.18, 1.18, 1.08, 1.09, 1.07 and 1.08 g feed/g gain for fish fed Diets 1–7, respectively. Results showed that more than 50% fish meal in rainbow trout diets could be replaced by plant protein meals without significantly reducing fish growth and increasing feed conversion ratio if these diets were supplemented with 0.4% or higher levels of lysine. Furthermore, lysine supplementation increased CP and lysine, and reduced fat levels in whole trout body (P 88%) in all diets, ADCs of dry matter were in the range of 72.0–75.6%, and ADCs of phosphorus varied from 47.7% to 61.8%.

The influence of dietary lipid source and alpha-tocopheryl acetate level on product quality of rainbow trout (Salmo gairdneri)

Abstract Rainbow trout ( Salmo gairdneri ) were fed practical diets containing either fish oil or swine fat and supplemented with 0, 50, 500, or 1500 mg of alpha-tocopheryl acetate per kg of diet for 4 months prior to harvest. The effects of diet on sensory attributes, fatty acid composition, tissue alpha-tocopherol level, and lipid oxidation during forzen storage were determined. Dietary fat source or alpha-tocopheryl acetate did not significantly affect sensory attributes of trout fillets evaluated fresh or after prolonged frozen storage. The fatty acid composition of the muscle and viscera were influenced by dietary fat source, most markedly in the levels of n −3 and n −6 fatty acids. Tissue alpha-tocopherol levels were significantly increased at dietary levels of 500 and 1500 mg alpha-tocopheryl acetate per kg diet. The dietary level of alpha-tocopheryl acetate required to prevent vitamin E deficiency signs was higher in fish fed the fish oil diet than in the fish fed the swine fat diet. Fish fed diets containing 500 and 1500 mg alpha-tocopheryl acetate had lower levels of malonaldehyde after frozen storage at −80°C for 4 months, but not after frozen storage at −20°C for 10 months.

9 – Diet Formulation and Manufacture

Publisher Summary Diet formulation and manufacture are exercises in compromise between the ideal and the practical. The perfect feed formulation that meets the nutritional needs of an animal or fish must always be modified to be less than ideal so that it can be manufactured. Diet formulation and manufacture are not independent activities. When feeds are formulated, the pelleting characteristics of mixtures are just as important as the nutritional content of the mixture. Production diets must be economical to manufacture, ship, store, and deliver to the fish. Pellets must remain intact in water until fish consume them. This ensures adequate intake of nutrients that might otherwise leach out of the pellets and minimize water pollution caused by disintegrating pellets. Thus, the way in which feed ingredients are chosen, prepared, combined, and processed is influenced by many factors, and compromise between the ideal and the practical is a necessity requiring a solid foundation of knowledge and experience. Rising concerns about the effects of fish farming on the aquatic environment, coupled with concerns about the dependence of fish feeds on fish meal produced from fully utilized or over-utilized wild fish stocks, have also influenced fish feed formulation and manufacture.

Metabolic response to dietary phosphorus intake in rainbow trout (Oncorhynchus mykiss)

Abstract The objectives of this study were to determine which indicators were most responsive to suboptimal phosphorus intake in fingerling rainbow trout, and to observe the magnitude of these changes over time. Fish with an initial mean weight of 1.8 g were hand-fed one of five semipurified wheat-gluten based diets containing between 0.23%–1.16% dietary phosphorus, or a fish meal control diet (1.8% P) for 8 weeks. Phosphorus, calcium and magnesium concentrations in whole body, skin (with scales), and plasma were measured bi-weekly. Alkaline phosphatase activity was determined in plasma and in a crude intestinal homogenate. There was no correlation between dietary phosphorus concentration and body weight of rainbow trout. Of all tissues and metabolites examined, skin was the most responsive to differences in dietary phosphorus concentration. Dietary treatment had a significant effect on the concentrations of ash, phosphorus, calcium and magnesium in rainbow trout skin at weeks 4 and 8. Whole body ash, phosphorus, calcium, and magnesium concentrations were also highly responsive to graded levels of dietary phosphorus at week 8. Rainbow trout fed suboptimal phosphorus diets had significantly lower plasma phosphorus concentrations and alkaline phosphatase activity, and significantly higher whole body lipid than those fed adequate phosphorus diets. Alkaline phosphatase activity of the intestinal homogenate was not significantly correlated with dietary phosphorus intake.