James H. Tidwell

Fish as food: aquaculture's contribution. Ecological and economic impacts and contributions of fish farming and capture fisheries.

Historically, the oceans were considered limitless and thought to harbour enough fish to feed an ever‐increasing human population. However, the demands of a growing population, particularly in poorer countries, now far outstrip the sustainable yield of the seas. At the same time as fishing has become more industrialised, and wild fish stocks increasingly depleted, aquaculture production—fish and shellfish farming—has grown rapidly to address the shortfalls in capture fisheries. But aquaculture has come under intense scrutiny and criticism as environmentalists fear that it could cause significant environmental problems and further impact wild species that are already threatened. Indeed, both capture fisheries and aquaculture must have environmental costs—all human activities of significant scale do—but it is necessary to fairly evaluate and compare the ecological and economic impact of both. In fact, a thorough analysis shows that the ecological threat of aquaculture is much lower than continuing to supply the majority of fish protein from wild capture. Fish is a vital source of food for people. It is mans most important single source of high‐quality protein, providing ∼16% of the animal protein consumed by the worlds population, according to the Food and Agriculture Organisation (FAO) of the United Nations (1997). It is a particularly important protein source in regions where livestock is relatively scarce—fish supplies <10% of animal protein consumed in North America and Europe, but 17% in Africa, 26% in Asia and 22% in China (FAO, 2000). The FAO estimates that about one billion people world‐wide rely on fish as their primary source of animal protein (FAO, 2000). > A consistent source of fish is essential for the nutritional and financial health of a large segment of the worlds population Fish also has substantial social and economic importance. The FAO estimates the value of fish traded internationally to be US

Use of soybean meal and distillers grains with solubles as partial or total replacement of fish meal in diets for channel catfish, Ictalurus punctatus

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Effect of partially or totally replacing fish meal with soybean meal on growth of blue catfish (Ictalurus furcatus)

Abstract A 12-week feeding trial was conducted in aquaria with juvenile (11g) channel catfish to examine effects of partially or totally replacing fish meal with a fixed percentage (35%) of distillers grains with solubles (DGS) and a variable percentage (up to 50%) of soybean meal in prepared diets. Four isonitrogenous (33% protein) and isocaloric (2.9 kcal digestible energy/g of diet) diets were formulated to contain 12, 8, 4, and 0% fish meal. Soybean meal was added to assure crude protein levels of 33%. A fifth diet was formulated identical to the diet with 0% fish meal, but with supplemental lysine and methionine added. After 12 weeks, weight gain, individual weight, individual length, food conversion ratio, specific growth rate, and survival were not significantly different ( P > 0.05) among treatments. These data suggest that a diet with all plant protein sources (soybean meal and distillers grains with solubles) can totally replace fish meal in a channel catfish diet.

Effects of dietary protein and lipid levels on growth and body composition of sunshine bass (Morone chrysops X M. saxatilis) reared in cages

A 12-week feeding trial was conducted in aquaria with juvenile (6 g) blue catfish to examine effects of substituting soybean meal for fish meal in a prepared diet. Four isonitrogenous (34% protein) and isocaloric (2.4 kcal digestible energy/g) diets were formulated to contain 13, 9, 4, and 0% menhaden fish meal (67% crude protein). Soybean meal (44% crude protein) was added in increasing percentages (48, 55, 62, and 69%) to the respective diets. A fifth diet, otherwise identical to the diet containing 0% fish meal and 69% soybean meal, was prepared with soybean meal that had been heated at 105 ° C for 60 min prior to diet preparation. After 12 weeks, fish fed a diet with 13% fish meal had a significantly (P 0.05) in body weights of fish fed the other four diets. No significant differences (P > 0.05) were found in percentage survival, food conversion ratio, and protein efficiency ratio among diets. Growth of blue catfish was similar to that reported for channel catfish juveniles. However, these data suggest that blue catfish juveniles require at least 13% fish meal in a diet containing 34% crude protein for optimal growth.

Growth and body composition of channel catfish (Ictalurus punctatus) fed diets containing various percentages of canola meal

Abstract Juvenile sunshine bass with an average weight of 125 g were stocked into 24 floating cages (1.2 × 1.2 × 2.4 m) and fed one of 8 practical diets formulated to contain various percentages (30, 36, 42, and 48%) of protein. Due to differences in composition of feed ingredients, diets were analyzed as having 29, 36, 41, and 46% protein. Each protein level was formulated with two lipid levels: low (between 6.5 and 9.8%) and high (between 13.3 and 17.1%). Fish meal composed a constant percentage (56%) of the dietary protein in all diets. Fish were stocked at a rate of 200 per cage and fed twice daily at 08.00 and 16.30 h. Fish were fed all they would consume in 30 min for approximately 150 days. Percentage weight gains and specific growth rates (SGR) of fish fed diets containing 41 and 46% protein (99 and 116 mg protein/kcal, respectively) were higher (P 0.05) in survival or feed conversion ratio (FCR) were found among treatments. Percentage dress-out, abdominal fat, hepatosomatic index, and body composition of sunshine bass was affected by dietary protein and energy level (P

Relative prawn production and benthic macroinvertebrate densities in unfed, organically fertilized, and fed pond systems

A 12-week feeding trial was conducted in aquaria with juvenile (10 g) channel catfish to examine the effects of partially substituting canola meal for soybean meal in prepared diets. Six isonitrogenous (32% protein) and isocaloric (2.7 kcal digestible energy g−1) diets were formulated to contain 0, 12, 24, 36, and 48% canola meal (CM). There were two diets with 0% CM; one with 8% fish meal (FM) and one with 4% FM. All diets with CM had 4% FM. Fish were fed twice daily all they could consume in 20 min. After 12 weeks, fish fed a diet with 8% FM and 0% CM had significantly higher (P < 0.05) percentage weight gains than fish fed all other diets. Fish fed diets containing 12 and 36% CM had significantly higher (P < 0.05) percentage weight gains (average 604%) than fish fed a diet containing 48% CM. Feed conversion ratio (FCR) of fish fed a diet containing 48% CM was significantly (P ≤ 0.05) higher (2.25) than values for fish fed 12, 24, and 36% CM. There were no histological differences in the thyroid of fish fed any of the diets. These data suggest that channel catfish can be fed diets containing up to 36% CM without adverse effects on growth or body composition. Fish fed a diet with 48% CM had a lower percentage weight gain compared with fish fed diets containing between 12 and 36% CM, possibly due to reduced palatability of the diet. Use of canola meal in practical diets for channel catfish may allow producers and feed mills to formulate more economical diets by adding another plant protein source to ingredients used in commercial catfish diets.

Effects of dietary protein level on second year growth and water quality for largemouth bass (Micropterus salmoides) raised in ponds

Abstract Relative prawn production rates in unfed, organically fertilized, and fed pond systems were evaluated. Populations of benthic macroinvertebrates that potentially serve as forage organisms in these systems were also evaluated and compared with ponds without prawns to evaluate forage preferences. Juvenile prawns (x = 0.36 ± 0.02 g) were stocked into nine 0.04 ha ponds at a density of 39 520 ha −1 . Prawns in three ponds were not fed, prawns in three ponds were fed a complete diet, and three ponds received organic fertilization. Three additional ponds (0.02 ha) served as controls (not stocked with prawns and received no nutrient input). Survival averaged 86%, overall, and was not significantly different among treatments. Average weights of prawns fed complete feed or raised in fertilized ponds (36 and 33 g, respectively) were not significantly different ( P > 0.05). Prawns in unfed ponds were significantly ( P ≤ 0.05) smaller (13 g). Average prawn yields in fed, fertilized, and unfed ponds (1261, 1056, 426 kg ha −1 , respectively) were all significantly different ( P ≤ 0.05). In ponds receiving no nutrient input, macroinvertebrate densities were significantly higher ( P ≤ 0.05) in ponds without shrimp (controls) than in those stocked with shrimp. In ponds stocked with shrimp, macroinvertebrate densities in fed and fertilized treatments were significantly greater ( P ≤ 0.05) than in the unfed treatment, but not significantly different ( P > 0.05) from each other. Insect taxa showed a greater negative response to prawn predation than non-insects. Non-insect taxa demonstrated a more positive response to fertilizer and feed than insects. Although prawn production in organically fertilized ponds was surprisingly high (>1000 kg ha −1 ), economic analysis demonstrated higher net returns when prawns were fed a prepared diet, principally due to the production of greater numbers of large, high value prawns.

Effect of Protein Level and Feeding Frequency on Growth and Body Composition of Cage-Reared Channel Catfish

Abstract Juvenile largemouth bass (122.1 ± 2.6 g), trained to accept artificial diets, were stocked into nine 0.04 ha ponds at a density of 12350 fish ha −1 and fed one of three practical diets containing either 42, 44, or 47% protein (dry weight). Fish meal composed a constant percentage (53%) of the dietary protein in each diet. Fish were fed all they would consume in 30 min once daily for 12 months (May 1994–May 1995). At final harvest, fish fed the 47% protein diet had significantly higher ( P −1 ), and survival (99%), and significantly lower ( P P > 0.05) from fish fed either 42% or 47% protein. Averaged over the study period, total ammonia-nitrogen (TAN) concentrations were significantly higher ( P P

Effects of complete and supplemental diets and organic pond fertilization on production of Macrobrachium rosenbergii and associated benthic macroinvertebrate populations

Abstract Channel catfish (Ictalurus punctatus) fingerlings were stocked in eight 1.25-m3 floating cages at densities of 320 fish/m3 and fed to satiety once or twice daily for 105 d with diets containing either 34 or 38% protein. Experimental diets were formulated by a commercial feed mill with recommended levels of essential amino acids, vitamins, and minerals. Fish fed a diet containing 38% protein had significantly (P 0.05) were found when body composition was analyzed in relation to dietary protein level, feeding frequency, and their interaction. These data indicate that channel catfish reared in cages may require a diet with a hi...

Growth, Feed Conversion, and Protein Utilization of Female Green Sunfish × Male Bluegill Hybrids Fed Isocaloric Diets with Different Protein Levels

Growth and population characteristics of freshwater prawns, Macrobrachium rosenbergii, fed either a complete diet, a supplemental diet (with fish meal replaced and vitamin and mineral supplements deleted), or the supplemental diet with an adjunct organic pond fertilization regime were examined. Effects of these treatments on potential forage organisms (benthic macroinvertebrates) were also evaluated. Juvenile prawns averaging 0.46 ± 0.49 g were stocked into nine 0.02 ha earthen ponds at 39 520 ha−1. Treatments were evaluated in triplicate ponds. There were significant differences (P 0.05) between regression lines for prawns fed the complete diet and those fed the supplemental diet with an organic pond fertilization regime. At harvest, yield, survival, individual weight, and feed conversion averaged 943 kg ha−1, 76%, 31 g, and 3.9, respectively over the three treatments. Deletion of vitamin and mineral supplements and replacement of fish meal in prawn diets was associated with a significant reduction (P < 0.05) in total benthic macroinvertebrate populations, possibly due to increased predatory pressure by prawns. In ponds in which prawns were fed the supplemental diet, organic fertilization resulted in a significant increase (P < 0.05) in total benthic macroinvertebrates and a 15% increase in average prawn weight at harvest. Results indicate that prawns may increase predation when essential nutrients are deleted from prepared diets and that the supply of potential forage organisms may be increased by organic fertilization.