Digestibility and feeding value of some feed ingredients fed to tilapia Oreochromis niloticus (L.)

The apparent digestibility of protein, organic matter and energy of high‐fibre and fibre‐reduced sunflower cakes, Kenya's ‘omena’ fishmeal, anchovy fishmeal and wheat bran were investigated in tilapia Oreochromis niloticus (L.) fingerlings. The feeding values and protein qualities of the above ingredients were also determined at two dietary protein levels. Fourteen diets were formulated, and each was provided to three tanks containing 12 fish in Expt 1 (digestibility study) and 25 fish in Expt 2 (feeding trial). Water temperatures and dissolved oxygen concentrations were maintained above 26 °C and 5.5 mg L^?1 respectively. Anchovy and ‘omena’ fishmeals each had an apparent digestibility coefficient for protein (ADC‐P) of 90%, whereas the fibre‐reduced and high‐fibre sunflower cakes had ADC‐P values of 89% and 86%. Wheat bran had an ADC‐P value of 75%, which was significantly lower than those found for the other test ingredients. Apparent digestibility coefficients for energy (ADC‐E) and digestible energy values (DE) were 86% and 78% and 4003 kcal kg^?1 and 3624 kcal kg^?1 for anchovy and omena fishmeals respectively. The corresponding values for the plant protein sources were 42% and 30% and 2200 kcal kg^?1 and 1400 kcal kg^?1 for the fibre‐reduced and high‐fibre sunflower cakes respectively. Diets based on the fibre‐reduced cake had higher levels of all amino acids than those based on the high‐fibre cake. Fish fed diets with 30% protein gained 40 g and had a feed conversion ratio (FCR) of 1.87, whereas those fed diets with 20% protein gained 35 g and had a FCR of 2.2. The source of protein had a significant effect on weight gain.     

Salmon testes meal as a functional feed additive in fish meal and plant protein‐based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and Nile tilapia (Oreochromis niloticus L.) fry

Fishery processing by‐products are a large resource from which to produce fishmeal and other products for a variety of uses. In this study, testes meal (TM) produced from pink salmon processing by‐product was evaluated as a functional ingredient in aquafeeds. Nile tilapia and rainbow trout fry were fed five isonitrogenous and isoenergetic experimental diets for 4 and 9 weeks respectively. Two diets were fishmeal‐based (FM) and three were plant protein‐based (PP). Salmon TM was added to the FM and PP diets at 7% to replace 20% of fishmeal protein (FMTM and PPTM respectively). An additional control diet was prepared in which fishmeal was added to the PP diet to supply an equivalent amount of protein as supplied by TM (PPFM). Inclusion of TM in both the FM‐ and PP‐based diets resulted in higher final body weights, although differences were only significant between rainbow trout fed FM or FMTM diets. Similar differences were calculated for other indices of fish performance, e.g. specific growth rate, feed conversion ratio, protein efficiency ratio and protein retention efficiency. Feed intake was significantly higher for fish fed FMTM compared with FM in rainbow trout. For tilapia, final weights were numerically higher, but not significantly different for fish fed diets containing TM compared with non‐TM diets (FM vs. FMTM; PP vs. PPTM). Performance of trout or tilapia fed the PPFM diet did not increase compared with the PP diet. The results indicate that TM addition to both FM and PP diets increased feed intake and also increased metabolic efficiency, demonstrating that TM can be a functional ingredient in aquafeeds.     

A test of a feed budget model for rainbow trout, Oncorhynchus mykiss (Walbaum)

A feed budget model, which enables farmers to adapt a general model to local conditions, was tested on rainbow trout, Oncorhynchus mykiss (Walbaum). The model has two major components; component 1 is used to calculate the energy required for one unit of biomass gain (g or kg) and component 2 estimates the daily growth increment (g or kg). Both components can be adjusted in relation to prevailing environmental conditions and, together, they express the daily energetic requirement of the specific species or strain. Fish fed using the model as a guide had a high rate of growth and good feed conversion. The model accurately predicted growth over the experiment, and is presented as a means of calculating the daily feed budget in fish farming. Growth of fish fed using self-feeders is presented for comparison with the results obtained using the model.     

Effects of stocking density and feeding levels on growth and feed efficiency of Nile tilapia (Oreochromis niloticus L.) fry

The effects of stocking density and feeding levels on larval survival, growth rates, feed utilization efficiency and body composition of Nile tilapia (Oreochromis niloticus L.) fry were investigated in two consecutive experiments. In experiment 1, swimup fry (0.016 g average body weight) were stocked in 20‐L fibreglass tanks, in a closed, recirculating indoor system, at five stocking densities (3, 5, 10, 15 and 20 fry L^?1) and fed a larval test diet (40% crude protein) to apparent satiation, three times a day, for 40 days. Fish survival, percentage weight gain and specific growth rate (% SGR) were negatively correlated with stocking density. The best performance was achieved at 3 fry L^?1. However, no significant differences in growth parameters were found between 3 and 5 fry L^?1. Body composition was not significantly affected by stocking density. In experiment 2, fry (0.016 g average body weight) were stocked at 5 fry L^?1, and fed a larval test diet (40% crude protein) at six feeding levels (10%, 20%, 25%, 30% and 35% BW day^?1) and to satiation, three times a day for 40 days. Fish growth rates and survival were extremely poor at 10% feeding level, and improved significantly with increasing feeding levels up to 30%, and levelled off with further increase in feeding levels. On the contrary, feed conversion ratio (FCR) and protein production value (PPV) were negatively correlated with feeding level. The lowest feeding level (10%) produced significantly lower body lipid and higher protein and ash than other feeding levels. The present results suggest that the optimum stocking density and feeding level of Nile tilapia fry are 5 fry L^?1 and 30% per day respectively.     

Effect of feed colour on growth and feed utilization of Nile tilapia (Oreochromis niloticus L.) larvae and fingerlings

Two experiments were conducted to investigate the effects of feed colour on the performance of Nile tilapia (Oreochromis niloticus) larvae and fingerlings. In the first experiment, triplicate groups of newly hatched larvae (0.01 g fish⁻¹) were stocked in 40 L glass aquaria at a density of 2 fish L⁻¹. The fish were fed a test diet (400 g kg⁻¹ crude protein) with six different colours (dark blue, dark green, red, dark brown, yellow and light brown) for 60 days. The best performance and survival were achieved in fish fed on dark‐coloured diets, while light‐coloured diets (yellow and light brown) resulted in inferior performance. Dark diets also produced higher body protein than light diets. Body water, lipids and ash showed irregular trends. In the second experiment, triplicate groups of Nile tilapia fingerlings (5.30 g fish⁻¹) were stocked in 140‐L aquaria, in a recirculating indoor system. The fish were fed a test diet (350 g kg⁻¹ crude protein) with the same colours used in the larval trial, for 60 days. Growth rates, feed efficiency, survival and body composition were not significantly affected by feed colours. These results suggest that Nile tilapia larvae are visual feeders, and they prefer dark‐coloured diets to light‐coloured diets, while fingerling fish showed no preference to diet colours.     

Effect of feeding different grain sources on the growth performance and body composition of tilapia, Oreochromis niloticus (L.)

Growth performance and body composition of tilapia Oreochromis niloticus (L.), fed isonitrogenous and isoenergetic diets containing different grain sources (maize, wheat, barley, sorghum and rice) at a level of 25% were studied for a period of 62 days. Fish fed a diet containing sorghum showed the maximum weight grain, highest specific growth rate (SGR, 2.23), the best feed conversion (FCR, 1.07) and protein efficiency ratio (PER, 2.42) in comparison with all other diets. The diets containing maize, wheat and rice did not show any significant (P < 0.05) differences between each other. The barley diet showed the poorest values (SGR, 2.05; FCR. 1.34; PER, 1.98: and NPR, 30.65) in comparison with others. Although the diet containing sorghum showed the best net protein retention (NPR, 36.21) values, the results did not differ (P > 0.05) among maize, wheat and sorghum diets. The sorghum diet produced fish with lower moisture but higher body fat contents as compared to others. The fish fed diets containing maize, wheat, barley and rice did not show any significant difference (P > 0.05) in their body moisture and fat contents. The source of grain in the diet did not affect the crude protein and ash contents of fish (P > 0.05). It is suggested that cereal grains at the 25% level can efficiently be utilized in tilapia diets, sorghum being the best.     

The effect of different numbers of feeding days on feed consumption and growth of rainbow trout [Oncorhynchus mykiss (Walbaum)]

A trial was conducted to evaluate the effects of the number of feeding days on feed consumption and growth of rainbow trout, Oncorhynchus mykiss (Walbaum) (initial mean weight 53.6 ± 11.3 g). Fish were held under natural winter–spring (40°57′N) photoperiod (L:8 D:16 – L:14 D: 10) and ambient water temperatures (4–12 °C) for 128 days, and fed on day 7 (F₇), day 5 (F_5.1: no feeding on weekends and F_5.2: no feeding on Sundays and Wednesdays) or every other day (F_EOD). Feeding treatments were replicated with 50 fish held in 200‐L tanks. Number of feeding days affected final live weight, with fish in group F₇ achieving a mean weight of 285.6 g, followed by F_5.1 (256.6 g), F_5.2 (247.6 g) and F_EOD (223.2 g). Final condition factors (CF) differed between the F_EOD group and the others. Feed conversion ratios (FCR) exhibited significant differences among some of the groups. The results suggest that depriving rainbow trout of feed for more than 1 day a week has a negative effect on growth, but little influence on feed conversion.     

Effect of feeding level on growth and nutrient deposition in rainbow trout (Oncorhynchus mykiss Walbaum) growing from 150 to 600 g

The effects of feeding level on growth and energy partitioning were studied in rainbow trout growing from 150 to 600 g. Triplicate groups of fish (initial weight 158 g fish^?1) were fed a practical diet at various feeding levels (25%, 50%, 75% and 100% of near satiation) for 24 weeks at 8.5°C. The final body weights of fish were 235, 381, 526 and 621 g. Restricted feeding levels significantly reduced live weight gain. Feeding levels had less pronounced effects on feed efficiency ratio, which were 0.98, 1.08, 1.02 and 0.83, respectively, for the 25%, 50%, 75% and 100% feeding levels. The growth of fish fed to near satiation was accurately described by the thermal‐unit growth coefficient. The growth data also showed that the widely used specific growth rate was not an appropriate model. Fish fed at the lowest feeding level (25%), which represented a maintenance ration (energy gain was less than 2 kJ fish^?1 day^?1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. The efficiency of energy for growth (k_g) was estimated to be 0.63. The factorial multiple regression approach estimated that the partial efficiencies of metabolizable energy utilization for protein deposition (k_p) and lipid deposition (k_f) were 0.63 and 0.72, and that maintenance energy requirement was about 19 kJ (kg BW^0.824)^?1, for rainbow trout held at 8.5°C.     

Modulation of the response of rainbow trout (Oncorhynchus mykiss Walbaum) to confinement, by an ectoparasitic (Argulus foliaceus L.) infestation and cortisol feeding

The effects of a 21 day infestation with the ectoparasite Argulus foliaceus on the response of rainbow trout Oncorhynchus mykiss to an acute stressor (confinement) were investigated. Fish were divided into a control and two parasitized groups, with one parasitized group having received cortisol feeding 72 and 24 h before infection. Prior to confinement only control fish showed a significant increase in body mass and condition factor. Following 4 h confinement, plasma glucose levels in the normal- fed/infested group were significantly higher than in the controls, while the cortisol-fed/infested group had significantly lower plasma levels of adrenocorticotropic hormone (ACTH) and glucose. Both infested groups, but not controls, had higher plasma ACTH and cortisol levels 48 h after confinement when compared with their pre-confinement levels. Stressor-induced immunomodulation was more evident in the parasitized fish after confinement, as was concluded from decreased lysozyme activity, alternative complement activity and oxygen radical production either immediately after, or 48 h post 4 h confinement. Circulating lymphocyte numbers were significantly reduced in the control and normal-fed/infested fish. Results indicate that low ectoparasitic infestations can, for a prolonged period, lead to a stress experience with effects that impair the response to subsequent stressors. Such effects may be further confounded by a previous elevation of plasma cortisol levels.     

Effects of iodized feed on stress modulation in steelhead trout, Oncorhynchus mykiss (Walbaum)

In the aquaculture industry, the physiological systems of fish can be chronically stressed by various biological, chemical and physical factors. Chronic stress leads to a decrease in the overall health and growth of the fish, making them more prone to diseases. Dietary iodine has been shown to reduce this stress response in chickens and increase disease resistance in dairy cattle, but the mechanisms by which iodine affects stress resistance and immunocompetency is not completely understood and has not been extensively studied in fish. This study investigated the effects of iodized feed as a nutritional supplement in relation to stress modulation in steelhead trout (Oncorhynchus mykiss). We investigated effects on primary, secondary and tertiary stress responses by measuring plasma levels of cortisol, glucose and thyroid hormones as well as haematocrit percentage and average growth rate in steelhead trout. Iodine‐supplemented fish, on average, had lower levels of plasma cortisol and glucose and lower packed cell volumes than fish fed with regular commercial feed (P<0.05). Iodine‐supplemented fish also showed higher levels of thyroid hormones and exhibited better growth over the period of the experiment (P<0.05). It was concluded that, used with other husbandry practices, use of iodine‐supplemented feed could lead to better host defence, growth and survival in fish raised in the aquaculture industry.     

Effect of enzyme supplementation to dehulled lupin-based diets on growth, feed efficiency, nutrient digestibility and carcass composition of rainbow trout, Oncorhynchus mykiss (Walbaum)

High inclusion levels of dehulled lupin (Lupinus angustifolius) in salmonid diets significantly decrease growth rates. This may be caused by the high concentrations of non‐starch polysaccharides including oligosaccharide (OS) in lupin. The antinutritive effects of OS have not yet been fully investigated in fish. The objective of this study was to determine the effect of enzyme supplementation of dehulled lupin‐based diets on the fish performance. There were two control diets: a fish meal‐based diet with no plant protein (FM) and a diet that contained 50% dehulled lupin (L). Four experimental diets based on diet L and containing four different exogenous enzyme supplements were used: diet L(E) (Energex^™); diet L(B) (Bio‐Feed^™ Pro); diet L(α) (Alpha galactosidase^™); and diet L(Mix), which contained all the enzymes. Fish were randomly stocked into tanks in duplicate groups of 38 fish, 16.58±0.169 (SE) g, and were fed twice a day for 6 weeks. The supplemented enzymes did not improve weight gain in fish fed lupin‐based diets. However, mixed enzyme significantly improved Protein Efficiency Ratio (PER). Apparent digestibility of DM, CP and GE significantly improved in fish‐fed L(E) diet. None of the supplemented enzymes affected digestive tract indices or carcass composition. Surprisingly, weight gain was significantly higher in fish‐fed L(α), L(E) and L(Mix) diets as compared with FM diet. Feed intake was significantly higher in fish‐fed L, L(α) and L(E) diets compared with the FM diet. It is concluded that storing of lupin kernel under a suitable condition may have partially hidden the positive effects of exogenous enzymes through activating the endogenous enzymes.     

Microwave irradiation and pelleting method affected feed chemical composition and growth performance and feed utilization of sex‐reversed Nile tilapia,Oreochromis niloticus (L.)

Microwave processing and pelleting methods were assessed to improve aquafeed quality for sex‐reversed Nile tilapia. The 2 × 3 experimental feeds were prepared with and without microwave irradiation of ingredients prior to pelleting with either a meat mincer, extruder or steam conditioner followed by a meat mincer. Five feedstuff ingredients, including fish meal, meat and bone meal, soybean meal, broken rice and rice bran, were irradiated separately at optimal times, according to the third‐order polynomial regression analysis between in vitro digestibility and microwave irradiation times (r = 0.681–0.942, P < 0.001, n = 42). The prepared feeds were studied for chemical compositions and responses in fish growth performance and feed utilization efficiency. The fish (1.57 ± 0.01 g initial weight) were fed ad libitum for 4 months. All proximate chemical compositions of experimental feeds, except protein, were influenced by microwave processing, pelleting methods or their interaction (P < 0.05). There were no significant effects from either parameter on water quality during the fish trial. Fish fed steamed microwave‐irradiated feed, mechanically pelleted with a meat mincer, showed the highest growth performance (weight gain 18.91 ± 0.73 g and specific growth rate 2.15 ± 0.26% day^?1) and feed utilization efficiency (feed conversion ratio 1.31 ± 0.05 g feed g gain^?1 and protein efficiency ratio 2.27 ± 0.08 g gain g protein^?1) compared with the other dietary groups. These findings indicate that microwave irradiation of feed ingredients prior to steam conditioning followed by mincing can improve aquafeed production quality.     

Induction of clinical aspergillomycosis by feeding contaminated diet to tilapia, Oreochromis niloticus (L.)

Abstract. Oreochromis niloticus maintained at 17°C and 26°C were fed a pelleted diet contaminated with cultures of Aspergitlus flavus fungus. Affected fish stopped feeding within one week, and became inactive, dark and oedematous. Exophthalmia, often accompanied by corneal or humoral changes, was common and mortalities commenced after 4 weeks. Surviving fish were sacrificed after 5 weeks and the fungus was isolated from all organs, including—irregularly—the eye. The histopathology was predominantly that of a necrotizing septicaemia, with fungal hyphae present in liver, peritoneum, kidney, intestinal wall and, distinctively, in the orbit and eye of affected fish.     

An in vitro method to determine phosphorus digestibility of rainbow trout Oncorhynchus mykiss (Walbaum) feed ingredients

An in vitro method was developed to assess the digestibility of phosphorus in 12 plant and animal feed ingredients for rainbow trout Oncorhynchus mykiss (Walbaum). The method simulates the gastrointestinal tract of the rainbow trout with regard to pH and gastrointestinal enzymes. Phosphorus solubility was measured after acid digestion (pH 3) with and without gastric enzymes, after alkaline digestion (pH 9) with and without intestinal enzymes, and after a two-step process involving acid and alkaline digestion. Commercially available digestive enzymes from mammals were compared with digestive enzymes from rainbow trout. Correlating in vitro digestibility with in vivo digestibility showed that acid digestion with both commercial enzymes ( r ²=0.98, P  < 0.05) and trout enzymes ( r ²=0.94, P  < 0.05) predicted the in vivo digestibility of animal feed ingredients. Alkaline digestion with both enzyme systems (commercial r ²=0.79; trout r ²=0.74, P  < 0.05) or without ( r ²=0.82, P  < 0.05) enzymes predicted the in vivo digestibility of ingredients from animal byproducts but not those from plant products. The in vitro digestibility with two enzyme steps (acid and alkaline) predicted in vivo digestibility of plant and animal ingredients ( r ²=0.79 for commercial enzymes and r ²=0.74 for trout enzymes) better than did one-step acid or alkaline digestion.     

Transfer of toxaphene and chlordane into farmed rainbow trout, Oncorhynchus mykiss (Walbaum) via feed

The study was carried out to quantitate the transfer of toxaphene and chlordane compounds from commercial fish feed into the edible part of rainbow trout, Oncorhynchus mykiss (Walbaum) under normal rearing conditions. Trout were fed with unspiked high energy feed for salmon (fat content 26–30%) over a period of 19 months. The average weight of trout increased from 10 g to more than 2092 g, reaching sizes of 51 cm length. Considerable amounts of toxaphene and chlordane residues were transferred from fish feed into trout muscle. Toxaphene concentrations increased up to 8.6 µg (Σ toxaphene indicator compounds 1–3) kg^?1 wet weight (w.w.) and chlordane reached 5.3 µg Σoxy‐, trans‐, cis‐chlordane + t‐nonachlor kg^?1 w.w. Results are also discussed on the contaminant levels based on the fat content and the effect of sexual maturation is considered in this study. The data allow the establishment of transfer rates for toxaphene and chlordane congeners from high energy diet into the edible part of farmed rainbow trout.     

Compensatory growth of Nile tilapia Oreochromis niloticus,L. subjected to cyclic periods of feed restriction and feeding in a biofloc system

The compensatory growth, productive performance, proximal composition and somatic indices of Nile tilapia (Oreochromis niloticus) cultivated in biofloc were evaluated during a 144‐day period under five cyclic regimes of feed restriction and feeding. Five treatment groups, in which the frequency of feed restriction (R) and feeding (F) varied by periods (days) as follows: R1:F3, R3:F9, R6:F18, R8:F24 and R12:F36; each treatment was evaluated in triplicate. The cycles were repeated throughout the culture period. The control group received feed daily. Fish were cultivated in 18 circular tanks (3 m³) at a density of 50 fish/m³ per tank. At the end of the study, the survival of Nile tilapia was greater than 90% in all the treatments. Complete compensation in growth was achieved in R6:F18 and R12:F36. At the end of the feed restriction period, both crude protein and total lipid content of the tilapia muscle tissue taken from fish of the treatment groups were similar to samples of muscle tissue derived from fish of the control group; however, a reduction of more than 40% in somatic indices compared with the control was observed, but these recovered by the end of the feeding phase. The results indicate that cyclic feeding based on 12 days of feed restriction and 36 days of feeding (R12:F36) induced a complete compensation in weight and restoration of energy reserves, with similar measures of productive performance observed when compared to the control treatment during the culture of Nile tilapia in biofloc, and food reduction did not affect proximal composition.     

Relationships between growth and disease resistance in rainbow trout,Oncorhynchus mykiss (Walbaum)

Rainbow trout from 23 families were evaluated for growth and resistance to the bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum and infectious haematopoietic necrosis (IHN) caused by IHN virus. Average family weights were between 161 and 263 g with an average of 225 g at 213 days post‐fertilization with specific growth rates ranging from 2.37 to 2.88. Per cent survival of fish challenged with F. psychrophilum was between 18% and 100%, while for those challenged with IHNV, the range was between 12% and 93%. Significant positive correlations were found for end body weight and resistance to IHN (P < 0.05) and for early body weight and resistance to BCWD (P < 0.1). However, no significant correlations were detected between resistance to both pathogens or disease resistance and overall genetic diversity or diversity within the major histocompatibility locus.     

Effect of temperature and feed ration on energy utilization in large rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract In one experiment, temperature and feed ration were varied for rainbow trout, Oncorhynchus mykiss (Walbaum), with an initial size of about 1200g. In two experiments the feed ration was varied between parallel tanks, with naturally fluctuating ambient temperatures, and containing rainbow trout with an initial size of about 1000g and 400–550g, respectively. Growth and feed efficiency were measured in all experiments. An ad libitum feed ration without wastage produced the most effective energy utilization in most experimental groups. At best an average of 50% of the gross energy was utilized for growth. The relation between growth rate and feed ration was linear, and there was no optimum point for feeding below this level. The observed intake of energy is compared with growth, measurements of digestibility, feeding and starving metabolism. It is also linked to earlier observations of intake by rainbow trout fingerlings to give equations expressing the energy needs of rainbow trout of different sizes (30–1500g). These are intended to be used for efficient rearing at different temperatures (10–22°C).     

Influence of dietary fat level and increased adiposity on growth and fat deposition in rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout, Oncorhynchus mykiss (Walbaum), (initial weight ～ 90 g) were fed diets differing in fat content (27.5% versus 12.6%) to examine the effects of dietary fat level on growth and fat deposition. During phase 1, which was run for 11 weeks, the fish were fed either a high- (27.5%) or low-fat (12.6%) diet. The fish were held at 14.5 °C under a 24 h:0 h light:dark photoperiod and were fed for 4 h each day during this phase. Subsequently, in phase 2, both diets were presented simultaneously, and the influence of adiposity on growth and fat deposition was examined in a growth trial which lasted for 8 months. There were no significant differences in body weights at the end of phase 1 (360.7 ± 7.7 g versus 348.2 ± 18.7 g for the fish on the high- and low-fat diets, respectively), but body composition was influenced by the fat content of the diet. The trout fed the high-fat diet had higher viscerosomatic indices (VSI: 11.7 ± 2.0% versus 9.1 ± 0.7%) and higher visceral fat contents (per cent fat: 38.0 ± 6.7% versus 23.3 ± 3.7%) than trout fed the low-fat diet. The percentage fat contents of the carcass (per cent fat: 12.4 ± 1.0% versus 9.3 ± 0.7%) and whole body (per cent fat: 15.4 ± 1.6% versus 10.5 ± 0.7%) were higher amongst the trout fed the high-fat diet, and these fish had a higher energy gain than those fish fed the low-fat diet. Differences in adiposity between the trout fed the high- and low-fat diets did not result in any differences in weight gain when the fish were provided with both diets simultaneously. During phase 2, the fish that had previously been fed the low-fat diet deposited more fat than those fed the high-fat diet during phase 1. The latter maintained whole body fat concentrations at ± 15% (phase 1: 15.4 ± 1.6%; phase 2: 15.2 ± 1.2%), whereas the fish that had been fed the low-fat diet increased their body fat concentration during phase 2 (phase 1: 10.5 ± 0.7%; phase 2: 14.7 ± 1.3%). Thus, there were no significant differences between groups in either body weight or proximate composition by the end of the experiment.