Santosh P. Lall

Effects of dietary phytase and cholecalciferol on phosphorus bioavailability in rainbow trout /Oncorhynchus mykiss

A study was conducted to examine the influence of dietary inclusion of phytase and high levels of cholecalciferol on phytate phosphorus (P) utilization of rainbow trout. Triplicate groups of rainbow trout, initial weight 51.6 g, were fed in excess diets containing 0 or 1500 units phytase kg−1 and 2500, 250,000 or 2,500,000 IU cholecalciferol kg−1 for 12 weeks. The basal diet provided 5.8 and 3.2 g total and phytate P kg−1 dry matter, of which most was derived from soy protein concentrate. Weight gain of fish was increased by phytase supplementation but decreased by higher cholecalciferol concentrations. Inclusion of phytase improved P availability as indicated by significantly higher apparent availability of P and bone ash and plasma and body P concentrations. Dietary cholecalciferol content did not influence P utilization. An increase in dietary cholecalciferol concentration caused higher deposition of calcium, magnesium and zinc in the kidney. Both cholecalciferol and phytase supplementation significantly (P<0.05) increased the hepatic cholecalciferol concentration. In summary, dietary phytase supplementation was effective in reducing P load of rainbow trout fed soybean protein concentrate-based diet. High levels of cholecalciferol (250,000 and 2,500,000) had no beneficial effect on P utilization.

Dietary phosphorus requirement of juvenile haddock (Melanogrammus aeglefinus L.)

A study was conducted to determine the quantitative requirement, excretion, availability and deficiency signs of phosphorus in haddock. Triplicate groups of haddock (4.2±0.01 g) were fed diets containing 0.42, 0.62, 0.82, 1.02 and 1.22% P and 19 MJ digestible energy (DE) per g of diet to satiation for 12 weeks. The basal diet, containing 0.42% P (0.08 g available P per MJ DE), was supplemented with graded levels of calcium phosphate, Ca(H2PO4)2. H2O, to formulate the five experimental diets. The fish were reared in seawater (salinity, 32‰) at a temperature of 12±2 °C. The growth, feed conversion ratio, vertebrae and opercula ash and urinary phosphate excretion were positively correlated with dietary phosphorus levels. Vertebrae ash increased from 44.5% to 56.6±0.47% and operculum ash from 31.4% to 48.2±0.56% of fat free dry matter with increasing dietary phosphorus content. Phosphorus requirement was estimated by using a quadratic equation for vertebrae ash. The data suggest that a diet of 0.96% total phosphorus, or 0.72% available phosphorus or 0.34 g available phosphorus per MJ DE, is required for haddock fingerlings. Plasma and urinary phosphate excretion increased with increasing dietary phosphorus levels and ranged from 0.4–1.5±0.03 to 0.1–7.9±0.2 mmol−l, respectively. The availability of organic phosphorus was 43.2±0.86%, however, inorganic phosphorus was highly available (99±1.23%). Signs of phosphorus deficiency were characterized by poor growth, loss of appetite, poor bone mineralization, deformed vertebrae and an increase in body lipid content.

Feeding frequency affects food consumption, feeding pattern and growth of juvenile yellowtail flounder (Limanda ferruginea).

Feeding experiments were carried out on juvenile yellowtail flounder (Limanda ferruginea) (6.8±0.2 g), a candidate for cold-water aquaculture in eastern North America. At about 7 °C, feeding frequency was shown to have a significant (P<0.05) effect on food consumption and growth, with fish fed to apparent satiation in two or four daily meals consuming more food and growing better than fish fed less often (once daily and two meals every other day). Fish fed two meals every other day ate significantly more (P<0.05) in the morning (8.4±0.4 mg) than in the afternoon (6.0±0.2 mg), whereas there were no differences in meal sizes between feedings for other groups. Behavioural observations revealed that fish fed fewer meals per day ingested more pellets per feeding (1.1±0.1 vs. 0.7±0.1 pellet/min), showed more activity and foraged more often throughout the day than fish fed four times daily or twice daily (3.5±0.3 vs. 2.1±0.2 behaviour/min). Low incidences of aggression indicated that yellowtail flounder probably do not form feeding hierarchies; however fish fed twice daily showed a significant increase in the coefficient of variation (CV) for body weight over the course of the experiment (P<0.05). Fish fed twice daily gained significantly more weight (P<0.05) and had the lowest FCR (0.89), thus it is recommended that fish at this stage of grow-out be fed twice per day.

Atlantic Salmon (Salmo salar): The “Super-Chicken” of the Sea?

In this article, the definition of sustainability is discussed, particularly in relation to the use of marine feed resources. The current review gives an overview of the development of Atlantic salmon (Salmo salar) aquaculture and how it has evolved due to changes in legal and management framework conditions. Atlantic salmon production is characterized with high utilization of nutrients, a high yield of production, and a large demand for rendered by-products. All of these factors compare favorably to production of most terrestrial farm animals. Historically, salmon feed has contained fishmeal and fish oil as the primary protein and fat source. Rising demand for feed ingredients has not increased pressure on forage fish resources. Rather, there has been an increased use of plant protein and fat sources. Increased utilization of plant ingredients may not be as sustainable as often claimed. Provided that marine harvest is carried out within legal frames, harvesting the marine ecosystem is a sustainable operation, and at present, the only significant source of long chain n-3 fatty acids. It is concluded that Atlantic salmon farming can be compared to raising a marine “super chicken” being among the most sustainable meat products in the world food market.

Utilization of glucose, maltose, dextrin and cellulose by juvenile flounder (Paralichthys olivaceus)

A study was conducted to determine the ability of juvenile flounder to utilize different sources of carbohydrate in their diets. Triplicate groups of fish (average weight, 4 g) were hand-fed visual satiety one of seven diets containing 15% cellulose, 15% glucose, 15% maltose, and 5–25% dextrin for 45 days in flush-out aquarium system. Weight gain, feed efficiency ratio, protein efficiency ratio (PER), energy retention efficiency, hepatosomatic index (HSI), and liver glycogen were measured. Fish fed the diet containing 15% cellulose had the lowest weight gain (P<0.05) among all groups. Weight gain of fish fed the diets containing 15% maltose and 15–25% dextrin was higher than that of fish fed the diets containing 15% cellulose and 5% dextrin. The feed efficiency ratio and PER of fish fed the diets containing 15–25% dextrin were significantly higher (P<0.05) than those of the other groups. Growth and feed utilization increased with an increase in the dextrin level of the diet. Lipid content of the whole body and liver decreased with an increase in dietary dextrin level. Liver glycogen and HSI of fish fed the 15% glucose and 15% maltose diets were higher (P<0.05) than those of fish fed the other carbohydrates, however these values were not affected by an increase in dextrin intake. Flounder (average weight, 15 g) were fasted for 48 h for a glucose tolerance test and blood was collected after feeding at 0, 1, 3, 5, 8, 11, 16, 24 and 48 h. Plasma glucose concentrations of fish fed the diets containing 15% glucose and 15% maltose peaked at 5–8 h (200 mg/100 ml) and 5 h (148 mg/100 ml), respectively, then decreased at 24 and 16 h. Fish fed the diets containing 5–25% dextrin showed a lower glucose level (87–97 mg/100 ml) than fish fed the other diets and it peaked between 3 and 5 h. Flounder utilized dextrin more efficiently than glucose, and dextrin was a better source of energy than lipid. The best growth and feed utilization were achieved with the diet containing 25% dextrin and 6% lipid.

Phosphorus utilization by Atlantic salmon (Salmo salar) reared in freshwater is not influenced by higher dietary calcium intake

Abstract To decrease the phosphorus (P) load of fish farms, factors affecting dietary P utilization need to be known in more detail. A study was conducted to examine the effect of dietary calcium (Ca) level on dietary P utilization of Atlantic salmon reared in freshwater. Salmon fingerlings (initial weight 42.1 g) were fed a semi-purified diet (1.3 g kg−1 Ca, 3.1 g kg−1 P) with or without Ca and P supplement for 15 weeks. Fish fed no P supplement showed bone deformities and low Ca and P content of vertebrae. An increase in supplementary Ca level from 0 to 1.5% (increase in Ca:P ratio from 0.2 to 2.1) had no significant effect on bone mineralization when dietary P content was at the requirement level of Atlantic salmon. Plasma phosphate concentration in fish fed diets supplemented with 5 g P kg−1 was decreased by dietary Ca supplementation of 15 g kg−1. An increase in supplementary Ca from 0 to 0.75% had a positive effect on bone mineralization when dietary P content was below the requirement level. Correlation between scale and bone mineralization was significant. Magnesium level in plasma and deposition in calcified tissue decreased with increasing dietary Ca and P levels. Hepatic cholecalciferol (vitamin D3) content was 58.5 ng g−1 in fish fed without Ca or P supplements, and 9–10 ng g−1 in fish fed with either Ca or P supplements indicating its involvement in the regulation of Ca and P homeostasis. The results suggest that in commercial salmonid diets, a high Ca:P ratio is unlikely to interfere with dietary P utilization. However, the possibility of improving the performance of plant protein based diets of low Ca:P ratio by Ca supplementation exists.

Amino acid composition of whole body tissue of Atlantic halibut (Hippoglossus hippoglossus), yellowtail flounder (Pleuronectes ferruginea) and Japanese flounder (Paralichthys olivaceus)

Abstract Amino acid and proximate composition of the whole body tissue of juvenile Atlantic halibut, yellowtail flounder and Japanese flounder were determined. Higher protein and lower lipid levels were found in whole body of Japanese flounder than the other two species. The amino acid composition was, however, not significantly different among species when expressed as g/100 g amino acids. The values were also found to be very similar to those of rainbow trout and Atlantic salmon. The A/E ratios [(each essential amino acid content/total essential amino acid content including cystine and tyrosine)×1000] based on the essential amino acid composition of whole body tissue, suggest that the amino acid requirements of flatfish may not be greatly different among species.

Effects of dietary protein level on growth and utilization of protein and energy by juvenile haddock (Melanogrammus aeglefinus)

In order to determine the optimum level of protein required in the diet of juvenile haddock, 750 fish with an average weight of 6.9 g were randomly distributed into each 15 tanks (320 l). Haddock were fed one of five isoenergetic diets containing 45%, 50%, 55%, 60% and 65% protein to satiation. All fish fed the experimental diets for 6 weeks had more than a three-fold increase in body weight, although no significant difference in weight gain was found among treatments. Feed/gain ratio decreased from 0.76 for fish fed 45% protein to 0.62 for fish fed 65% protein. Nitrogen (N) intake increased with an increase in dietary protein, which, in turn, resulted in an increase in N gain of fish whole body. Fish fed 45% protein gained 0.37 g N, which was not significantly different from that of fish (0.40 g) fed 50% protein. Nitrogen gain for fish fed the remaining two diets (55% and 60% protein) had the same value (0.43 g); that was significantly (P<0.05) higher than fish fed the diet containing 45% protein. The broken-line regression of N gain against dietary protein level yielded an estimated protein requirement of 53.8% (Y=0.43−0.006(R−XLR), R=53.8±2.08) on a dry-matter basis. Gross energy intake of fish varied from 283 to 229 kJ for fish fed 45% and 65% protein, respectively. The highest energy gain of 119 kJ was obtained with fish fed 50% protein, resulting in the highest energy retention efficiency of 44.1%. The hepatosomatic index of fish significantly (P<0.05) decreased from 10.7% to 7.3% as dietary protein level increased.

Effect of dietary lipid level on fatty acid β-oxidation and lipid composition in various tissues of haddock, Melanogrammus aeglefinus L.

Haddock (Melanogrammus aeglefinus) is a gadoid fish species that deposits dietary lipid mainly in the liver. The fatty acid (FA) beta-oxidation activity of various tissues was evaluated in juvenile haddock fed graded levels of lipid. The catabolism of a radiolabelled FA, [1-(14)C]palmitoyl-CoA, through peroxisomal and mitochondrial beta-oxidation was determined in the liver, red and white muscle of juvenile haddock fed 12, 18 and 24% lipid in the diet. There was no significant increase in the mitochondrial or peroxisomal beta-oxidation activity in the tissues tested as the dietary lipid level increased from 12 to 24%. Peroxisomes accounted for 100% of the beta-oxidation observed in the liver, whereas mitochondrial beta-oxidation dominated in the red (91%) and white muscle (97%) of juvenile haddock. Of the tissues tested, red muscle possessed the highest specific activity for beta-oxidation expressed on a per mg protein or per g wet weight basis. However, white muscle, which forms over 50% of the body mass in gadoid fish was the most important tissue in juvenile haddock for overall FA catabolism. The total lipid and FA composition of these tissues were also determined. This study confirmed that the liver was the major lipid storage organ in haddock. The hepatosomatic index (HSI; 10.0-15.2%) and lipid (73.8-79.3% wet wt.) in the liver increased significantly as dietary lipid was increased from 12 to 24% lipid. There was no significant increase in the lipid composition of the white muscle (0.8% wet wt.), red muscle (1.9% wet wt.) or heart (2.5% wet wt.).

Dietary protein requirement of juvenile American eel (Anguilla rostrata) fed practical diets

Abstract Triplicate groups of juvenile American eel were fed to satiation herring meal-based diets containing 35, 39, 43, 47 and 51% crude protein (as fed basis) for 84 days. Data were collected to determine the relationship between dietary protein level and the following response variables: mean weight gain (MWG), specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility and nutrient retention. Highest MWG and SGR ( P P P P P