Dominique P. Bureau

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 digestibility of rendered animal protein ingredients for rainbow trout Oncorhynchus / mykiss

Abstract The apparent digestibility of 20 rendered animal protein ingredients from various origins was determined in three digestibility trials. The ingredients consisted of eight blood meals, four feather meals, six meat and bone meals and two poultry by-product meals. Within each type of ingredient, a relatively large range of raw materials, processing conditions and equipment were represented. In each of three trials, a reference diet was mixed with test ingredients in a 70:30 ratio to produce a series of test diets. The reference and test diets were fed to rainbow trout reared at 15°C and fecal samples were collected using the “Guelph system”. Apparent digestibility coefficients (ADC) for protein and energy of the four feather meals varied between 81 and 87% and 76 and 80%. Significant differences in the ADC for protein of feather meal were observed and may be related to the drying equipment. The ADC for protein of the two poultry by-product meals was 87 and 91% and that of energy 77 and 87%. The ADC for protein and energy of the six meat and bone meals varied between 83 and 89% and 68 and 83%, respectively. Treatment of one of the meat and bone meals by air-classification to reduce its ash content resulted in a significant increase in the ADC for protein and lipid. ADC for protein of the blood meals varied between 82 and 99% whereas ADC for energy varied between 79 and 99%. Spray-dried blood products (whole blood, blood cells, blood plasma) were highly digestible (ADC protein=96-99%). Rotoplate-, steam-tube- and ring-dried blood meals had significantly lower ADC for protein and energy than spray-dried blood products.

The effects of purified alcohol extracts from soy products on feed intake and growth of chinook salmon (Oncorhynchus tshawytscha) and rainbow trout (Oncorhynchus mykiss)

Two studies were conducted to determine the effects of purified alcohol extracts (PAES) from soybean meal (PAES I) and soy protein isolate (PAES II) on feed intake, growth and intestinal mucosa of chinook salmon and rainbow trout. The PAES were prepared by an extraction process aiming at the isolation of soyasaponins. In the first study, a series of diets were formulated to have one half of the protein coming from fish meal and the other half from soy products. They included a control diet containing 32% soy protein concentrate (SPC diet) and a diet with 44% soybean meal (SBM diet). The SPC diet was supplemented with the PAES I (PAES I diet) to produce a diet with a saponin level similar to that expected to be found in the SBM diet. The SPC diet was also supplemented with Quillaja bark saponin at 0.15% (QBS15 diet) and 0.30% (QBS30 diet). Feeding the PAES I diet and the SBM diet resulted in complete suppression of growth of chinook salmon due to a dramatic reduction of feed intake (P<0.05). The PAES I diet significantly depressed the growth of rainbow trout (P<0.05). Feeding the QBS30 diet, but not the QBS15 diet, significantly depressed growth of chinook salmon and rainbow trout (P<0.05). Both the QBS15 and QBS30 diets caused significant intestinal damage. The PAES I diet had only a minimal effect on the intestinal mucosa of rainbow trout. The majority of the chinook salmon fed the PAES I diet had intestinal morphology representative of a fasting state which corresponded well with the observation that these fish stopped feeding early in the experiment. In the second study, a high fish meal diet was supplemented with 0.3% PAES II and fed to chinook salmon and rainbow trout. The PAES II diet had a highly significant effect on feed intake and growth of chinook salmon. This tended to reduce growth of rainbow trout although not significantly. The effect on feed intake of chinook salmon was statistically significant on the third day of feeding the PAES II diet. The two PAES diets used in these studies had potent feeding deterrent properties for chinook salmon and also affected growth of rainbow trout. We suggest that soyasaponins are responsible for the effect of these PAES.

Effects of feeding level and water temperature on growth, nutrient and energy utilization and waste outputs of rainbow trout (Oncorhynchus mykiss)

A study was carried out to determine the effect of feeding level and water temperature on growth and feed efficiency, nutrient and energy utilization and waste outputs of rainbow trout. A practical diet was fed to near-satiation to groups of fish reared at 6, 9, 12 and 15 °C. At each temperature, the feed intake of other groups of fish was restricted to about 85 % or 70 % of the amount of feed consumed in the previous week by the fish fed to near-satiation. Total feed intakes over 12 weeks were, on average, 76 % and 65 % of total feed intake of the near-satiety group for R1 and R2, respectively. Reducing the feed allocation resulted in significantly (P 0.05) effect on feed efficiency, carcass composition or efficiencies of digestible nitrogen and digestible energy retention. Increasing temperature resulted in an increase in the apparent digestibility of dietary dry matter, nitrogen and energy (P < 0.05). The increase in digestibility of dry matter and nitrogen with increasing temperature resulted in higher estimated total solid and solid nitrogen waste outputs per kg fish produced (P < 0.05) at lower water temperatures. Estimated dissolved nitrogen and phosphorus waste outputs (g/kg fish produced) were not affected by the feeding level or water temperature. A highly significant (P < 0.01) linear relationship was observed between metabolizable energy (ME) intake above basal metabolism and recovered energy. The efficiency of ME utilization for growth (Kpf) was 0.61 and this coefficient was not affected by feed intake or water temperature. Protein and lipid were deposited in a constant ratio (1 kJ protein gain: 1.4 kJ lipid gain) regardless of ME intake or water temperature.

Development of bioenergetic models and the Fish-PrFEQ software to estimate production, feeding ration and waste output in aquaculture

Feeding guides for salmonid fishes have been available from various sources for many years. These feeding guides have originated in one way or another from earlier feeding charts of the 1950-60s when meal-meat mixture diets were widely used. Few of the feeding guides available today are based on actual bioenergetics data at different water temperatures and are adapted to high energy diets. New feeding standards have been developed based on principles of nutritional energetics in which the digestible energy content of diet, digestible protein and energy ratio and the amount of digestible energy required per unit of live weight gain are taken into account. The gain expressed as retained energy in carcass and maintenance energy at different water temperatures is the main criteria for energy and feed allocations. Series of bioenergetic models were developed based on these principles and a stand-alone multimedia program was written to facilitate computation of the models. This program predicts growth and energy, nitrogen and phosphorus retention, requirements and excretions to determine feeding standards, waste outputs and effluent water quality based on a biological method. The models require initial and final body weights, water temperature, growth coefficient, carcass energy content and waste coefficients to estimate input and output. Accurate determinations of the thermal-unit growth coefficient, apparent digestibility coefficients and retention efficiencies are essential and these coefficients are determined by biological experiments in the laboratory and field. Oxygen requirement is included to aid environmental control in fish culture system. The Fish-PrFEQ program also contains modules for production records, performance calculations and data base management for input and output data which may be exported for further data and graphic manipulations.

Feather meals and meat and bone meals from different origins as protein sources in rainbow trout (Oncorhynchus mykiss) diets

Two feeding trials were conducted to evaluate the potential of feather meal and meat and bone meal as protein sources in rainbow trout diets and as well as to compare the nutritive value of ingredients from different origins. Three feather meals were used in a 20-week trial with fish reared at 8.5°C. The feather meals, alone or in combination with corn gluten meal and blood meal (steam-tube dried), replaced herring meal in diets formulated to be isoproteic (ca. 47% digestible protein (DP)) and isoenergetic (ca. 22 MJ/kg digestible energy (DE)) assuming apparent digestibility coefficient (ADC) values for protein and energy of 75% for the three feather meals. Three meat and bone meals were used in a 12-week trial with fish reared at 15°C. Increasing levels of meat and bone meal replaced herring meal in diets formulated to be isoproteic (ca. 43% DP) and isoenergetic (ca. 19 MJ/kg DE) based on ADC for protein of 85% and ADC for energy of 70% for the three meat and bone meals. The incorporation of up to 15% feather meal (providing about 20% of total DP) in the diet was possible without affecting growth, feed efficiency, nitrogen or energy gains of the fish. The incorporation of up to 24% meat and bone meals (providing about 25% of total DP) in the diet was possible without affecting growth but resulted in a small yet significant reduction in feed efficiency compared to control diet. No significant differences were observed among feather meals and meat and bone meals from various origins. The results from this study show that feather meal and meat and bone meal have good potential for use in rainbow trout diets.

Phosphorus utilization by rainbow trout /Oncorhynchus mykiss : estimation of dissolved phosphorus waste output

Phosphorus (P) waste output, notably in the dissolved form (DWP), is a major concern for many fish culture operations. Fish are believed to excrete DWP via the urine but this aspect has never been examined in detail. A better understanding of P utilization and renal P handling of fish could aid development of nutritional strategies for the management and reduction P waste. Rainbow trout were fed high corn gluten meal diets, supplemented with dibasic calcium phosphate, containing increasing P levels (0.75, 1.15, 1.66 and 2.19%). P utilization was examined in a 16-week growth trial. A second trial was conducted to determine urinary inorganic P (Pi) excretion using a non-invasive technique involving the use of a glomerular filtration marker and spot-sampling of urine. A third trial was conducted to measure DWP output through P accumulation in water. Increasing dietary P intake had no significant effect on growth and feed efficiency but significantly increased whole carcass and vertebrae P content. Efficiency of P retention decreased with increasing P intake. DWP represented 25, 47, 63 and 71% of digestible P intake as digestible P increased from 0.29, 0.62, 0.94 to 1.27%. Above a “threshold” plasma inorganic P (Pi) concentration (86 mg Pi l−1), urinary Pi excretion was related to plasma Pi in a linear fashion and could be estimated as follows: urinary Pi output [mg kg−1 body weight (BW) day−1]=−360+4.2 plasma Pi (mg l−1); (R2=0.82, P<0.001). DWP output estimates, based on P accumulation, were 10, 63, 75 and 112 mg kg−1 BW day−1 for fish fed the diets with 0.29, 0.62, 0.94 and 1.27% digestible P, respectively. The DWP output of these fish, estimated from the difference between digestible P intake and expected P retention, were 7, 29, 58 and 92 mg kg−1 BW day−1. Urinary Pi excretion rates, estimated based on plasma Pi of the fish, were 0, 21, 94, 101 mg kg−1 BW day−1. This study suggests that plasma Pi is the main factor determining DWP output of fish and that plasma Pi measurements could help in the estimation of P adequacy of the diet or DWP output.

Reduction of Waste Output from Salmonid Aquaculture through Feeds and Feeding

Abstract The main goal of aquaculture is to efficiently convert feed into fish and shellfish. Inherent to this practice is the generation of waste; however, from a waste management viewpoint, aquaculture differs in important respects from terrestrial animal farming. Measurement of actual feed intake is nearly impossible; consequently, unconsumed feed contributes a relatively large proportion of total waste output in most operations. Moreover, containment of wastes is difficult, and wastes are rapidly dispersed into the surrounding waters. Monitoring and estimating quantitative waste outputs in effluent directly is an inaccurate and costly process. Other methods of estimating the waste output from aquaculture operations should be used. Because most aquaculture wastes are dietary in origin, efforts to reduce waste should focus on nutrition and feeding, including the formulation of special diets, development of feeding systems, and improvement of the efficiency of nutrient utilization. Modern low-pollution o...

Chemical Composition and Preliminary Theoretical Estimates of Waste Outputs of Rainbow Trout Reared in Commercial Cage Culture Operations in Ontario

Abstract Twenty-eight rainbow trout Oncorhynchus mykiss and six feed samples were obtained from two cage culture operations in Ontario and analyzed by proximate analysis. This information was then used to estimate the waste outputs of rainbow trout cage culture operations. Calculations of nitrogen (N), lipid, phosphorus (P), and gross energy (GE) gains by the fish were based on the theoretical growth curve predicted by a thermal-unit growth coefficient model, and the N, lipid, P, and GE contents of the fish were estimated by regression analyses. The feed required to achieve the predicted growth and energy gain was calculated based on digestible energy requirements that were determined by modifying published Fish-PrFEQ bioenergetics models (assuming a 5% feed wastage). The theoretical digestible energy requirement of rainbow trout growing from 10 to 1,000 g reared in cages was estimated at 22.7 MJ/kg weight gain. Under these conditions, rainbow trout fed the various feed sampled were predicted to have feed...

Effects of dietary fatty acid composition on the regulation of carnitine palmitoyltransferase (CPT) I in rainbow trout (Oncorhynchus mykiss)

Dietary fatty acid composition, particularly polyunsaturated fatty acids, can affect both genetic and non-genetic regulatory mechanisms of carnitine palmitoyltransferase (CPT) I, the main regulatory enzyme of mitochondrial fatty acid oxidation. We aimed to determine how these regulatory mechanisms were affected by changes in the fatty acid composition of the diet in fish. Specifically, we fed rainbow trout (Oncorhynchus mykiss) either a high polyunsaturated fatty acid (PUFA) diet, a high saturated fatty acid (SFA) diet or a mixed fatty acid control (CTL) diet for 8 weeks to determine if modifications of the dietary fatty acids would affect 1) the genetic expression of CPT I and its transcription factor peroxisome proliferator activated receptor (PPAR), 2) the mitochondrial membrane composition and if these modifications would affect CPT I sensitivity to malonyl-CoA, and 3) levels of malonyl-CoA in the tissues. We found that fish fed the high PUFA diet significantly increased CPT I mRNA expression in red muscle, liver and adipose tissue, while PPAR alpha and beta expressions were variable across tissues. Few significant changes were observed in the mitochondrial membrane composition with the exception of DHA in the red muscle. There were no significant differences in CPT I sensitivity to malonyl-CoA or the malonyl-CoA content of the tissues with either experimental diet. Our present data suggest that changes in gene expression of CPT I and PPARs is the main regulatory mechanism controlling CPT I function in fish using our experimental diet.