C.Y. Cho

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.

Development of high-nutrient-dense, low-pollution diets and prediction of aquaculture wastes using biological approaches☆

Abstract As with agriculture, aquaculture is a biological conversion process of food into animal production, but it differs, from a waste management viewpoint, from animal farming. Firstly, prediction of feed intake and optimum level of feeding are difficult, hence feed waste contributes a relatively large proportion of total waste output in most operations. Secondly, collection of wastes, both solid waste and soluble or dissolved waste, is also very difficult and wastes are rapidly dispersed into the surrounding water. These factors create many problems which are generally unknown to other animal farming operations. However, sustainable aquaculture can be maintained through nutritional strategies for the management of aquaculture waste (NSMAW) by minimizing waste outputs from the source. The basic principles are formulation of high-nutrient-dense diets and development of efficient feeding systems based on energetic data. Monitoring and quantitation of waste output is also carried out indirectly using digestibility measurements and comparative carcass analyses. This is a biological and nutritional approach rather than a conventional chemical approach to effluent analyses. These latter are laborious, inaccurate and expensive. Recent high-nutrient-dense (“low-pollution”) diet formulations output less than 200 kg solid waste and less than 5 kg P per tonne fish produced, but achieving this reduction of waste output requires completely revised feeding standards based on an average 15 MJ DE/kg salmonid fish produced.

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.

Effect of extrusion processing and steam pelleting diets on pellet durability, pellet water absorption, and the physiological response of rainbow trout (Salmo gairdneri R.)

Abstract The effect of extrusion processing and steam pelleting on pellet durability, pellet water absorption and the physiological response of rainbow trout reared upon these diets was investigated. Extruded pellets were observed to be more durable, had superior water stability and absorbed more water than steam pellets. Trout reared on extruded pellets had prolonged gastric emptying in comparison with those reared on steam pellets; this may have been responsible for the reduction in daily feed consumption. Trout reared on extruded pellets also showed significantly lower weight gain but higher feed efficiency than those reared on steam pellets. Liver: body weight ratio and percent liver glycogen were significantly higher in trout reared on the estruded pellets as compared with those reared on steam pellets. Thus, extrusion processing may increase the bioavailability of carbohydrate in the diet and the enlarged livers and increased liver glycogen content could impair liver function.

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.

The growth of rainbow trout (Salmo gairdneri) given diets containing chitin and its relationship to chitinolytic enzymes and chitin digestibility

The growth of rainbow trout fed diets containing 4, 10 and 25% chitin, over a 12-week period, was significantly depressed (P < 0.001) when compared with controls fed diets containing 25% starch. There was no difference in growth rate between control fish and those fed diets containing 10% N-acetyl glucosamine (GlcNAc). Isotopically labelled amino sugars were shown to be oxidized when injected intraperitoneally into rainbow trout. Relatively high levels were found of chitinase activity in the stomachs and of chitobiase in the intestines. These enzyme activities were similar in all the trout, irrespective of the amount of chitin in their diets, except that chitobiase in the intestines of fish fed diets containing GlcNAc showed higher levels of activity than the controls (P < 0.05). Chitin was not significantly digested when fed at 10 and 30% of the diet but the apparent digestibility of pre-cooked starch was 50% when fed at either 15 or 25%, on the basis of the inert indicator (Cr2O3) method. Chitinase and chitobiase activities were not reduced in fish fed diets containing 10% chitin and an antibiotic (Tribrissen®) although the alimentary microflora were completely eliminated. Enzyme activities were not enhanced when live chitinolytic bacteria (Vibrio alginolyticus) were incorporated into diets with 10% chitin; these bacteria were only recovered from the intestine. The evidence indicates an endogenous origin of chitinolytic enzymes in the trout gastro-intestinal tract. The presence of either antibiotic or bacteria in the diet had no effect on the digestibility of chitin.

The essentiality of cholecalciferol in the diets of rainbow trout (Salmo gairdneri)

Abstract 1. 1. Vitamin D3 was found to be essential in the diet of rainbow trout. 2. 2. Vitamin D3 deficiency in rainbow trout was characterized by a marked decrease in weight gain and feed efficiency, lethargy and anorexia, the clinical manifestations of tetany without hypocalcaemia. an increase in the lipid content of carcass, white muscle and liver, and increased carcass dry matter. 3. 3. Unlike mammals, bone and blood mineral stores appeared unaltered in vitamin D3 deficient rainbow trout. 4. 4. With trout maintained in water containing 30ppm of calcium, increasing the level of dietary calcium from 0.36% to 1.1% increased the amount of white muscle lipid and decreased the kidney magnesium levels, but exerted no effect on weight gain or feed efficiency, regardless of vitamin D3, status. 5. 5. Rainbow trout receiving feed containing 1000 i.u./kg of vitamin D3 showed no detectable amounts of 25-hydroxycholecalciferol or 24R. 25-dihydroxycholecalciferol in their blood plasma.

The synthesis, half-life and distribution of ascorbic acid in rainbow trout

Abstract 1. 1. Synthesis of ascorbic acid from [1- 14 C] glucose in yearling and mature rainbow trout is not conclusive at this time but may occur in some fish. 2. 2. The biological half-life of [1- 14 C]ascorbic acid in the head kidney of yearling rainbow trout on the basis of TLC- 14 C radioactivity analysis was approximately 20–21 days. 3. 3. The ascorbic acid levels in the tissues of rainbow on a replete diet showed that the highest concentrations were found in the female gonads, with the brain, head kidney, testes, spleen, liver, eyes, red muscle, white muscle and heart tissues having lower concentrations in that order. 4. 4. The ascorbic acid concentration in the ripe ovary would represent a considerable store of the vitamin, which would also suggest a critical function of this vitamin in the reproduction of this animal and the feeding of an ascorbic deficient diet to the brood stock could therefore impair the reproductive performance of the trout.

Effect of hypervitaminosis a on the development of ascorbic acid deficiency in underyearling rainbow trout (Salmo gairdneri R.)

Abstract The effect of hypervitaminosis A on the development of ascorbic acid deficiency was investigated in rainbow trout reared on a practical diet. Excess vitamin A (124 000 I.U./kg) in the diet, as retinyl-palmitate, did not appear to interact with ascorbic acid metabolism of the trout. This dietary level of vitamin A did not affect the occurrence of the ascorbic acid deficiency symptoms, lordosis and scoliosis. Vitamin A does not appear to be toxic to rainbow trout at the level of 124 000 I.U./kg of diet and it would appear that the development of lordosis and scoliosis was due in this case to ascorbic acid deficiency.