Comparison of the effects of four anaesthetics on biochemical blood profiles of perch

This study investigated the feasibility of using clove oil, 2-phenoxyethanol, or Propiscin as an alternative to tricaine methane sulphonate (MS 222) as a fish anaesthetic, particularly in regard to reducing fish stress. The biochemical blood profiles of perch Perca fluviatilis L. anaesthetized with either MS 222 (100 mg L⁻¹), clove oil (33 mg L⁻¹), 2-phenoxyethanol (0.40 mL L⁻¹) or Propiscin (1.0 mL L⁻¹), and a non-anaesthetized control group were compared. Biochemical profiles were determined from blood samples collected before treatment in controls. For each anaesthetic tested, fish were divided into two groups, one sampled immediately after 10-min anaesthesia and a second, sampled 24 h after 10-min anaesthesia. The values determined in the present study suggested that internal organs and tissues of perch were slightly altered by MS 222, clove oil and 2-phenoxyethanol anaesthesia, but not by Propiscin anaesthesia.     

Anaesthetic efficacy and physiological responses to clove oil-anaesthetized kelp grouper Epinephelus bruneus

The efficacy of clove oil as an anaesthetic and at producing a physiological response (plasma cortisol and glucose) was evaluated in the kelp grouper, Epinephelus bruneus . To acquire complete anaesthesia in less than 3 min and recovery in <10 min, three doses of clove oil were tested at 18, 22 and 26 °C. Although higher anaesthetic doses resulted in shorter induction times and longer recovery times, and a lower temperature resulted in longer anaesthesia induction and slower recovery, we found the optimal dose and administering temperature of clove oil to be 250–300 mg L⁻¹ at water temperature of 18 °C, 150–200 mg L⁻¹ at water temperature of 22 °C and 50–100 mg L⁻¹ at water temperature of 26 °C respectively. Following the administration of 150 mg L⁻¹ of clove oil at 22 °C, the plasma cortisol level was highest (4.24 ± 1.571 μg dL⁻¹) after 12 h and the plasma glucose was highest (92.7 ± 9.61 mg dL⁻¹) after 2 h. These results should be useful to the aquaculture industry, where anaesthesia is necessary for a range of activities.     

Efficacy of tricaine methanesulphonate and clove oil as anaesthetics for juvenile cobia Rachycentron canadum

Six experiments were designed to determine the optimal anaesthetic dosage of tricaine methanesulphonate (TMS) and clove oil that could be used safely on juvenile cobia Rachycentron canadum of two sizes [G1=4.9±0.8 g; G2=13.9±3.1 g]. We documented the stage of anaesthesia and the acute toxicity as 96 h LC₅₀ (lethal concentration 50% population) at various exposure times of the two anaesthetics. At 10 min induction time, the TMS 96 h LC₅₀ was 93.9 mg L⁻¹ in G1 and 97.0 mg L⁻¹ in G2. Compared with clove oil, the 96 h LC₅₀ was 60.0 mg L⁻¹ in G1 and 69.8 mg L⁻¹ in G2. The difference between the two groups (G1, G2) did not influence anaesthesia safety ( P >0.05). Rachycentron canadum achieved stage 3 anaesthesia more rapidly at a lower clove oil concentration level (40 mg L⁻¹, 10 min) than TMS (60 mg L⁻¹, 10 min), but the recovery period of clove oil, was significantly longer. Clove oil was the most effective in reducing the short-term stress induced by routine biometry (20 mg L⁻¹, 10 min) and also by transporting (1 mg L⁻¹, 8 h). Whereas, for long-term exposure, 40 mg L⁻¹ TMS was found to be safe.     

Comparative efficacy of MS-222 and benzocaine as anaesthetics under simulated transport conditions of a tropical ornamental fish Puntius filamentosus (Valenciennes)

There is a growing commercial interest in the fish, Puntius filamentosus , in the ornamental fish trade in India and elsewhere. The trade is, however, hampered by severe mortalities during transport of the fish owing to insufficient data available on the use of anaesthetics. To resolve this problem, we evaluated the efficacy of two anaesthetics, MS-222 and benzocaine, in sedating P. filamentosus in simulated transportation experiments and used stress response parameters such as cortisol and blood glucose levels to perform assessments. We observed that MS-222 at 40 mg L⁻¹ and benzocaine at 20 mg L⁻¹ were sufficient to induce sedation for 48 h. Above these concentrations, both the anaesthetics adversely affected the fish and resulted in mortalities. Both anaesthetics significantly lowered the blood cortisol and glucose levels compared with the unsedated controls. Importantly, the anaesthetics treatment significantly lowered the post-transport mortality in the fish. The results of the study show that MS-222 and benzocaine could be used as sedatives to alleviate transport-related stress in P. filamentosus to improve their post-transport survival and hence reduce economic loss.     

Potential benefit of clove oil sedation on animal welfare during salmon smolt, Salmo salar L. transport and transfer to sea

The purpose of this study was to determine the effect of clove oil (4.0 mg L⁻¹) sedation, compared with non-sedation, on the primary (plasma cortisol), secondary (osmoregulation) and tertiary (mortality) stress responses in Atlantic salmon smolts during transport and transfer to sea. Clove oil sedation during on- and off-loading sufficiently reduced the primary stress response to lower mortality (2.1%) during transfer to sea compared with unsedated fish, which experienced a mortality rate above 12.2%. The unsedated fish experienced an acute mortality that stabilized only 6 days after the transport. None of the secondary stress responses measured in this experiment could contribute towards explaining this phenomenon, with the possible exception of plasma magnesium (Mg²⁺). Plasma Mg²⁺ differed between the groups; while plasma Mg²⁺ in the clove oil sedated group returned to pre-stress levels 72 h after transport, the unsedated group showed no such recovery even 1 week after transport, which may indicate a disturbance in the hydromineral balance, and provides a plausible explanation for the delayed mortality in this group. Eugenol-based anaesthetics appear to be promising as a stress-reducing sedative for Atlantic salmon smolts, and, if used properly, this chemical could improve animal welfare and survivability during and after common aquaculture-related incidents.     

Efficacy of clove oil and ethanol against Saprolegnia sp. and usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss (Walbaum) eggs

Inhibitory concentrations of clove oil and ethanol against growth of Saprolegnia sp. hyphae were screened by a modification of the hemp (Cannabis sativa L.) seed MicroPlate (HeMP) method and their usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss eggs was tested. In vitro experiment showed that in continuous static exposure, clove oil at 100 mg L^?1 significantly inhibited the growth of Saprolegnia, whereas in bath exposures, clove oil at 500 mg L^?1 had no significant effect at any exposure time tested (15, 60 and 240 min), but clove oil at 10 000 mg L^?1 significantly inhibited growth at all exposure times. Clove oil and ethanol treatments had no visible effects on the onset or spread of the fungus during incubation of rainbow trout eggs. Clove oil at 1000 mg L^?1 resulted in 95–100% mortality before the eyed stage was reached. Sublethal concentrations of clove oil and ethanol had no effects on the development rate of the embryo or growth and yolk utilization efficiency after hatching. This study suggests that clove oil and ethanol may not be options in controlling aquatic fungi infestations during incubation of rainbow trout eggs.     

Reduced water oxygen levels affect maximal feed intake, but not protein or energy utilization efficiency of rainbow trout (Oncorhynchus mykiss)

This study examined the effect of reduced water oxygen levels on the utilization efficiencies of energy and protein from a diet fed to rainbow trout. An experimental diet was fed at one of the four ration levels with an additional starved treatment also included in each oxygenation regime. Oxygen levels in each oxygenation regime varied with ration level, but averaged 9.3 ± 0.36 mg L⁻¹ for the normal regime and 5.7 ± 1.4 mg L⁻¹ for the hypoxia regime. Significant differences were observed in the apparent satietal feed intake levels in each oxygenation regime, but not at any of the pair-fed restricted levels. No significant effects of oxygenation regime were observed on the utilization of either energy or protein by the fish. Efficiency of protein use varied depending on the protein intake level, but was not significantly affected by oxygenation regime. This study demonstrates that a reduction in the oxygen levels of the water does not affect the utilization efficiency of dietary digestible protein and energy in rainbow trout, but does result in a downregulation of feed intake when the fish is fed to apparent satietal levels.     

Continuous exposure to infectious pancreatic necrosis virus during early life stages of rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout, Oncorhynchus mykiss (Walbaum), were exposed continuously to infectious pancreatic necrosis virus (IPNV) at 0, 10¹, 10³ or 10⁵ plaque forming units (pfu) L⁻¹ of water to estimate the effects of chronic IPNV exposure on early life stages. Fish density averaged 35 fish L⁻¹ (low density) or 140 fish L⁻¹ (high density), and the tank flow rate was 250 mL⁻¹ min. Virus exposure began at 6 days before hatch and continued until fish were 44 days old. Cumulative per cent mortality, analysis of survival and hazard functions, and discrete-time event analysis were used to explore the patterns of survival and mortality. In eggs and fish exposed to IPNV, mortality significantly greater than in the 0 pfu L⁻¹ exposure did not occur until IPNV concentration was 10⁵ pfu L⁻¹ at low fish density and 10³ pfu IPNV L⁻¹ at high fish density. These results suggest that in the natural aquatic environment, where rainbow trout densities are likely to be considerably lower than in this study, mortality resulting from infection with IPNV will very likely not occur when ambient concentrations of virus are ≤10³ pfu IPNV L⁻¹. In aquaculture rearing units, trout density is likely to be as high or higher than the densities used in this study. Therefore, continuous inputs of virus at concentrations greater than 10¹ pfu L⁻¹ may result in IPN epidemics in aquaculture facilities.     

Distended, water-filled stomach in seawater farmed rainbow trout, Oncorhynchus mykiss (Walbaum), provoked experimentally by osmoregulatory stress

The present study evaluates if abdominal dis-tension caused by a water-filled stomach in seawater farmed rainbow trout, Oncorhynchus mykiss (Walbaum), and Atlantic salmon, Salmo salar L., could be provoked experimentally by live chilling in sea water (0.5 °C). Fifty rainbow trout and 50 salmon were visually classified, either as normal or suffering from the condition. Prior to chilling, no rainbow trout or salmon suffered from a water-filled stomach. During chilling, 25% of the rainbow trout and 2.5% of the salmon developed water-filled stomach. Affected rainbow trout had significantly higher blood plasma osmolality and significantly lower body weight than normal trout. The frequency of trout with a water-filled stomach increased significantly with increasing chilling time and increasing plasma osmolality. The regression coefficients revealed that the proportion of affected rainbow trout in-creased by 0.82% h⁻¹ of chilling and by 0.46% per unit increase in mosmol L^−1. The present study revealed that abdominal distension in seawater farmed rainbow trout was far more severe than in Atlantic salmon and could be provoked experimentally by osmoregulatory stress. This is consistent with the observation that water-filled stomach appear only occasionally in seawater farmed Atlantic salmon.     

Effects of a peroxide-based commercial product on bacterial load of larval rearing water and on larval survival of two species of Sparidae under intensive culture: preliminary study

Larvae of two Mediterranean Sparidae species, Sparus aurata and Dentex dentex , were used to test the efficacy of a peroxide-based product (Ox-Aquaculture^©) on the reduction in bacterial load in larval rearing water and its effects on larval survival. Eleven-day-old S. aurata larvae and 15-day-old D. dentex larvae were exposed to different concentrations of Ox-Aquaculture^© (50, 100 and 200 mg L⁻¹, and 20 and 50 mg L⁻¹ respectively) for 1 h. Results indicated that 50 and 20 mg L⁻¹ were the most effective concentrations for the reduction in bacterial load (at least one order of magnitude) after 1 h treatment, without affecting larval survival and/or vitality in 11 dph S. aurata and 15 dph D. dentex larvae respectively. Ox-Aquaculture^© concentrations of 200 and 50 mg L⁻¹ during 1 h affected negatively final survival rate of the larvae of S. aurata and D. dentex respectively.     

Effects of sulfamerazine on selected haematological and immunological parameters in rainbow trout (Onchorhynchus mykiss, Walbaum, 1792)

In the present study, effects of sulfamerazine on some haematological and immunological parameters of rainbow trout ( Oncorhynchus mykiss ) were examined. Four groups of rainbow trout were fed experimental diets containing either no sulfamerazine (control) or supplemented with sulfamerazine at 100 mg kg⁻¹ (Exp-A), 200 mg kg⁻¹ (Exp-B) or 400 mg kg⁻¹ (Exp-C) for 21 days. Blood samples were taken for the haematological and immunological parameters from fish on the third, seventh, 14th and 21st days of feeding. Haematological parameters [haematocrit, leucocrit, numbers of erythrocytes (RBC) and leucocytes (WBC), haemoglobin (Hb), mean corpuscular volume (MCV), mean haemoglobin concentration (MHC) and mean corpuscular haemoglobin concentration (MCHC)] and immunological parameters [phagocytic ratio (PR) and index (PI), glass-adherent NBT-positive cell activation, total plasma protein and total immunoglobulin (Ig)] were evaluated during the experimental trial. It has been observed that MCV ( P <0.05), PR and PI ( P >0.05) were increased and haematocrit and leucocrit value, numbers of erythrocytes and leucocyte, haemoglobin, MHC and MCHC values and total plasma protein and total Ig levels were decreased in rainbow trout after application of three different doses of sulfamerazine.     

Effect of combined photoperiod, water calcium concentration and pH on survival, growth, and moulting of juvenile crayfish (Procambarus clarkii ) cultured under laboratory conditions

The red swamp crayfish, Procambarus clarkii (Girard), is one of the most commonly farmed freshwater species in inland China due to its high market value and consumer demand. The aim of this study was to determine the optimum combinations of photoperiod, water calcium concentration and pH for juvenile survival, growth and moulting. In our orthogonal experiment, the three environmental factors were varied at three levels (photoperiod: 16L:8D, 12L:12D and 8L:16D; calcium concentration: 45.5, 65.5 and 85.5 mg L⁻¹; and pH: 6.8, 7.8 and 8.8). Range analysis showed that the maximum survival of juvenile crayfish occurred at photoperiods of 16L:8D or 8L:16D, water calcium concentration of 45.5 mg L⁻¹ and pH of 7.8; maximum weight gain at photoperiod 16L:8D, water calcium concentration 65.5 mg L⁻¹ and pH 7.8; maximum length increase at photoperiod 16L:8D, water calcium concentration 65.5 mg L⁻¹ and pH 7.8; and the highest moult frequency at photoperiod 12L:12D, water calcium concentration 65.5 mg L⁻¹ and pH 7.8. Analysis of variance indicated that photoperiod, water calcium concentration and pH significantly influenced only the weight gain of juvenile crayfish ( P <0.05). Taking growth into consideration, we suggest that a photoperiod of 16L:8D, calcium concentration of 65.5 mg L⁻¹ and pH 7.8 might be optimal conditions for rearing juvenile P. clarkii .     

Effects of anaesthesia with MS-222, clove oil and CO2 on feed intake and plasma cortisol in steelhead trout (Oncorhynchus mykiss)

We examined the effects tricaine methanesulfonate (MS-222), clove oil and CO₂ on feed intake and cortisol response in steelhead trout, Oncorhynchus mykiss. Even though a body of literature exists about the effects of different anaesthetics on fish, no comparative information seems to be available about their effects on feed intake after anaesthesia, which would be important to know especially in aquaculture research. We anaesthetised juvenile steelhead trout with these three anaesthetics, and then sampled them 4, 24 and 48 h later. Fish in all groups ate relatively well already 4 h after anaesthesia. However, feed intake in fish treated with clove oil or MS-222 was lower than in the controls. There were no differences in feed intake among anaesthetised groups. Plasma cortisol concentrations were elevated 48 h after anaesthetisation, but the treatment means were equal throughout the experiment. Our results support previous findings that clove oil is a reasonable alternative to MS-222.     

Pathogenicity of Saprolegnia species associated with outbreaks of salmonid saprolegniosis in Japan

The present study was conducted to evaluate the pathogenicity and pathology of Saprolegnia salmonis NJM 9851 and Saprolegnia parasitica NJM 9868, isolated from outbreaks of saprolegniosis, against the immature stages of five species of salmonids. The cumulative mortalities of the tested fish groups that were exposed to 2 × 10 ⁵  spore/L concentrations of S. salmonis NJM 9851 were 90% for brown trout, 93.3% for sockeye salmon and 100% for rainbow tout, masu salmon, and Japanese char. In contrast, all salmonid species exposed to 2 × 10 ⁵  spore/L concentrations of S. parasitica NJM 9868 experienced cumulative mortalities of 100%. The histopathological changes of the saprolegniosis lesions found in all sites of infection were loss of the epidermis, edema of the hypodermis and different degrees of degenerative changes in the underlying musculature. It is clear from our results that S. salmonis NJM 9851 and S. parasitica NJM 9868 are highly pathogenic species to five species of salmonid fishes     

The synthetic antioxidant, ethoxyquin, adversely affects immunity in tilapia (Oreochromis niloticus)

Ethoxyquin (EQ) has been used as an antioxidant in livestock, aquaculture and pet foods. Animal food safety law has established the upper limit of EQ in animal feed at 150 mg kg⁻¹. However, the risk of EQ at the approved level for aquaculture feed (150 mg kg⁻¹) to fish health is unknown. Here, we examine the effect of EQ on the immunity of tilapia ( Oreochromis niloticus ). EQ concentration in the blood reached 0.16 mg L⁻¹ in fish fed EQ at the approved level. This level of EQ inhibited phagocytic activity of leucocytes in vitro and antibacterial activity of whole blood in vivo . Furthermore, pyknosis in the liver was observed throughout the duration of feeding. However, after 30 days of experimental challenge with feed containing 150 mg kg⁻¹ of EQ, no significant difference was observed in mortality. Although EQ at the approved level in feed causes immunosuppression in fish, the severity of immunosuppression does not lead to a lowering of disease resistance for short feeding periods.     

Total calcium and inorganic phosphate in the blood plasma of farmed rainbow trout, Oncorhynchus mykiss

Reference (physiological) value intervals determined by the lower 2.5% and upper 97.5% quantiles were calculated for total calcium (Ca _t ) and inorganic phosphate (P) in farmed rainbow trout, Oncorhynchus mykiss , at an age of 10–12 months in raceway culture. Total calcium levels were significantly ( P ≤0.0009) greater in males (2.63–4 mmol L⁻¹, n =47, mean weight 359±142 g) than in immature females (2.48–3.97 mmol L⁻¹, n =410, mean weight 400±145 g). The reference range for P in immature females and males was 3.09–9.32 mmol L⁻¹ ( n =467, mean weight 401±144 g). The distribution and density of the quantiles in the tested reference group were made possible by the use of histograms, which showed normal distributions for Ca _t in males but not for Ca _t and P in immature females and males, in which a sinistral asymmetry was found.     

Evaluation of lipid spray beads for the delivery of water-soluble materials to a marine suspension-feeder, the Manila clam Tapes philippinarum (Deshayes 1853)

We describe the development and evaluation of a new microparticle for delivering low-molecular weight, water-soluble materials to suspension feeders. Spray beads successfully incorporated materials dissolved in an aqueous phase or as dry particulate, within a triacylglyceride bead composed of tripalmitin, 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ triolein, or 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil.
Riboflavin was successfully incorporated (up to 44 mg g⁻¹ lipid) and retained (up to 98% over 24 h in seawater) as dry particles in all three mixtures of lipid. Aqueous oxytetracycline hydrochloride or polymeric dye were incorporated (45.6 mg g⁻¹ lipid and 18.1 mg g⁻¹ lipid, respectively) and retained best (99% and 94%, respectively) in spray beads composed of tripalmitin. The addition of triolein or fish oil to the lipid bead reduced incorporation and retention efficiencies for aqueous core materials by up to 75%.
Manila clam seed readily ingested and digested lipid microparticles, spray beads and lipid-walled microcapsules. Microparticles composed of tripalmitin were excreted with their payloads intact. Intact microparticles composed of 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil were largely absent in faecal strands suggesting successful release and delivery of microparticle contents to clams.
Spray beads composed of tripalmitin softened with 400 mg g⁻¹ fish oil represent an effective microparticle type for delivering low-molecular weight, water-soluble materials to aquatic suspension feeders.     

Effect of plant active compounds on immune response and disease resistance in Cirrhina mrigala infected with fungal fish pathogen, Aphanomyces invadans

The antibacterial activity of individual and mixed medicinal plant compounds, azadirachtin (Az), camphor (Ca) and curcumin (Cu), was tested at 100, 200, 300, 400, 500, 600 and 700 ppm (mg L⁻¹) against fungal fish pathogen, Aphanomyces invadans, in vitro . At the lower concentrations between 100 and 300 ppm, the mixture of the tri-herbal (Az+Ca+Cu) compound yielded a higher ( P >0.05) zone of inhibition (ZI) of 7 mm than the positive control; the maximum ZI values (8–15 mm) were realized between 400 and 700 ppm ( P <0.05). At the lowest minimum inhibitory concentration (MIC) the tri-herbal compound (100 ppm) yielded 13 colony-forming units; hence, this dose can be effectively used at the lowest concentration of 100 mg L⁻¹ to ward off the growth of A. invadans in vitro . In Cirrhina mrigala , intramuscular administration (100 μL) of the selected doses of 100, 400 and 700 ppm (mg L⁻¹) significantly enhanced ( P <0.05) the serum lysozyme activity (Ly), production of reactive oxygen species and reactive nitrogen species (RNS or NO) by peripheral blood leucocytes on the 10th, 20th and 30th day. A priori administration of the compound in the fish (100 ppm on 30th day) decreased the percentage mortality when challenged with the pathogen while in the untreated group the mortality increased ( P <0.05). This study indicates that intramuscular administration of the tri-herbal compound Az+Ca+Cu at a concentration of 100 ppm could augment the immune response in C. mrigala against A. invadans .     

Further development of bithionol therapy as a treatment for amoebic gill disease in Atlantic salmon, Salmo salar L.

This study examined the efficacy of bithionol as a prophylactic or therapeutic oral treatment for Atlantic salmon (AS), Salmo salar , affected by amoebic gill disease (AGD). Furthermore, it explored the interaction of bithionol oral therapy with the current standard treatment (a freshwater bath for at least 3 h). The efficacy of three medicated feeds was determined in the trial by feeding AGD-affected AS at 1% body weight (BW) day⁻¹ either oil coated commercial feed (control) or prophylactic and therapeutic bithionol at 25 mg kg⁻¹ feed. Feeding commenced 2 weeks prior to exposure to Neoparamoeba spp. at 300 cells L⁻¹ and continued for 49 days post-exposure (PE). Bithionol when fed as a 2-week prophylactic or therapeutic treatment at 25 mg kg⁻¹ feed delayed the onset of AGD pathology and reduced the percentage of gill filaments with lesions. Administration of a 3-h freshwater bath at 28 days PE significantly reduced amoeba numbers to a similar level across all treatments; in contrast, gross gill score and percent lesioned filaments were reduced to different extents, the control having a significantly higher score than both bithionol treatments. Following the freshwater bath, clinical signs of AGD increased at a similar level across all treatments, albeit controls were significantly higher than the bithionol treatments immediately following freshwater treatment. This study demonstrated that bithionol at 25 mg kg⁻¹ feed, when fed as a 2-week prophylactic or a therapeutic treatment, delayed and reduced the intensity of AGD pathology and warrants further investigation as a treatment for AGD-affected AS.     

Effects of dietary phosphorus and lipid levels on utilization and excretion of phosphorus and nitrogen by rainbow trout (Oncorhynchus mykiss). 2. Production-scale study

In a 8-week production-scale experiment at a commercial trout farm, the effects of dietary lipid level and phosphorus level on phosphorus (P) and nitrogen (N) utilization of rainbow trout (initial mean weight 99 g) were assessed. A low-phosphorus, high-lipid experimental diet (457 g protein, 315 g lipid, 9.1 g P  kg^–1 dry diet) was compared with a commonly used commercial diet (484 g protein, 173 g lipid, 13.6 g P  kg^–1 dry diet). P and N budgets were constructed using data from the production-scale experiment and digestibility data for the two diets. In addition, orthophosphate and ammonia-N waste were measured in effluent over one 24-h period. Relative to the commercial diet, the experimental diet resulted in significantly increased feed efficiency ratio, N retention and P retention, and substantially reduced dissolved, solid and total P waste (g kg^–1 dry feed). Although N retention resulting from the experimental diet was higher, this was attributable to higher N (protein) digestibility of the experimental diet. Solid N waste (g kg^–1 dry feed) resulting from the experimental diet was substantially lower, but dissolved N waste (g kg^–1 dry feed) was not significantly different relative to the commercial diet. Mean effluent orthophosphate production (mg day^–1 kg^–1 fish) of fish fed the experimental diet was substantially lower than that of fish fed the commercial diet ( P  < 0.05), but effluent ammonia-N production (mg day^–1 kg^–1 fish) was not significantly affected by dietary treatment.