Effects of dietary supplementation of alga Haematococcus pluvialis (Flotow), synthetic astaxanthin and β-carotene on survival, growth, and pigment distribution of red devil, Cichlasoma citrinellum (Günther)

Dietary carotenoids of various types and concentration can affect the pigmentation efficiency in an ornamental fish red devil, Cichlasoma citrinellum . Astaxanthin (AX) containing alga Haematococcus pluvialis , a synthetic AX, and a synthetic β-carotene (BC) were supplemented in formulated diets at two concentrations, 80 and 160 mg kg⁻¹, resulting in six pigmented diets. Formulated diet without carotenoids supplementation served as a control. These diets were fed to the fish, for 8 weeks. Astaxanthin dominated in body carotenoids deposition. Dietary BC hardly had contribution to body AX. Control fish had much lower AX content in skin, fin and muscle than fish fed pigmented diets, but had equal AX content in liver, intestine and gonad as those fish. Dietary synthetic AX had equal efficiency in depositing AX in skin and fin as natural AX but higher efficiency in gonad than natural AX. Fish fed AX supplemented at 160 mg kg⁻¹, either natural or synthetic AX, had higher AX content in skin than fish at 80 mg kg⁻¹ but had equal AX content in fin as fish at 80 mg kg⁻¹. Disregarding the treatment effects, the overall average AX content in tissue in descending order was gonad>fin≧(intestine=skin)>liver>muscle.     

Dietary vitamin E requirement of hybrid striped bass (Morone chrysops female × M. saxatilis male)

This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg⁻¹ from Na₂SeO₃ and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg⁻¹ as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg⁻¹ dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg⁻¹ had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg⁻¹. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg⁻¹ dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.     

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.     

Haematological response and growth performance of Nile tilapia (Oreochromis niloticus L.) fed diets containing folic acid

Haematological response and growth performance over 150 days, and resistance to a low-temperature stress of Nile tilapia fed diets with increasing folic acid (FA) levels were evaluated. The experiment was conducted in a completely randomized design with eight FA levels (0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 mg kg⁻¹ feed) supplemented in purified diets (32.0% CP and 13 398 kj DE kg⁻¹). One hundred and ninety-two fingerlings were randomly assigned to 32 net cages distributed in eight 1000 L aquaria with a physical and biological filter and a temperature control system (26.0 ± 1.0 °C). For cold-induced stress, fish were transferred to 24 30 L-aquaria with individual biofilters and aeration. The water temperature was gradually reduced until it reached 13 °C. Haematological parameters evaluated before and after cold stress were total erythrocytes and leucocytes count, differential leucocyte, haemoglobin, haematocrit, total plasmatic protein and haematometric indices. Growth performance parameters were mean weight gain, feed conversion ratio and survival. Dietary FA supplementation did not influence erythropoiesis under normal temperature conditions; cold stress impaired erythropoiesis, causing hypochromic microcytic anaemia and leucopoiesis, and also neutrophilia. Growth performance is influenced by folate and supplementation between 0.5 and 1.0 mg FA kg⁻¹ diet, which makes up for nutritional demands, guaranteeing production and health under appropriate temperature conditions.     

Supplemental citric acid and particle size of fish bone-meal influence the availability of minerals in rainbow trout Oncorhynchus mykiss (Walbaum)

Juvenile rainbow trout Oncorhynchus mykiss (Walbaum) were fed six low-phosphorus (P) diets supplemented with two different sizes of ground fish bone-meals (fine, 68 μm or less; coarse, 250–425 μm) and a coarse bone-meal diet containing four levels of citric acid (0, 4, 8 or 16 g kg⁻¹ diet) to investigate the effects of pH and bone particle size on P bioavailability. The basal diet provided 3.4 g P   kg⁻¹ and bone-meal increased P contents to 5.4–6.0 g P   kg⁻¹. Coarse bone-meal diets supplemented with 0, 4, 8 or 16 g kg⁻¹ of citric acid had pH values of 6.0, 5.7, 5.4 and 5.0, respectively. Weight gain and whole-body water, protein and lipid contents were not influenced by bone-meal supplementation. Supplementing the basal diet with both coarse and fine bone-meal significantly increased whole-body ash content. Fish fed no bone-meal were hypophosphataemic compared with fish fed with either fine or coarse bone-meals. Phosphorus in fine bone-meal had higher availability than P in coarse bone-meal. Bone-meal supplementation significantly decreased whole-body manganese content from 8.9 μg g⁻¹ in fish fed no bone-meal to 2.3 and 4.5 μg g⁻¹ in fish fed with fine and coarse bone-meals, respectively. The concentration of magnesium increased but zinc concentration was not affected by bone-meal supplements. Citric acid increased whole-body ash content but the influence of citric acid on the body P content was not significant ( P  = 0.07). Dietary acidification by citric acid significantly increased whole-body iron in a linear fashion. The bioavailability of dietary P can be improved by fine grinding the bone in fish meals.     

Optimum dietary soybean meal level for maximizing growth and nutrient utilization of on-growing gilthead sea bream (Sparus aurata)

Six isonitrogenous [450 g kg⁻¹ crude protein (CP)] and isoenergetic diets (23 kJ g⁻¹) with six levels of defatted soybean meal inclusion (0, 132, 263, 395, 526 and 658 g kg⁻¹) in substitution of fish meal were evaluated in gilthead sea bream of 242 g initial weight for 134 days. Fish fed diets S0, S13, S26 and S39 had a similar live weight (422, 422, 438 and 422 g, respectively) but fish fed diets S53 and S66 obtained the lowest final weight (385 and 333g, respectively), and similar results were presented in specific growth rate (SGR). Fish fed diets S53 and S66 also obtained the highest feed conversion ratio (FCR). Quadratic multiple regression equations were developed for SGR and FCR which were closely related to dietary soybean level. The optimum dietary soybean levels were 205 g kg⁻¹ for maximum SGR and 10 g kg⁻¹ for minimum FCR. Sensorial differences were appreciated by judges between fish fed S0 and S39 soybean level, but after a re-feeding period of 28 days with diet S0, these differences disappeared.     

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.     

Zinc gluconate and zinc sulphate as dietary zinc sources for Atlantic salmon

Different chemical forms of essential minerals and trace elements supplemented to feed may show different bioavailability in fish. The present experiment was performed to compare an organic zinc form (Zn-gluconate) with zinc sulphate as dietary zinc sources for Atlantic salmon. Triplicate groups of fish were fed commercial fish meal based diets supplemented with either a low zinc level (50 mg Zn kg⁻¹) or medium zinc level (180 mg Zn kg⁻¹) as zinc gluconate or zinc sulphate for 6 months. Growth, mortality and feed conversion were recorded through the experiment. Fish were sampled initially and every month for zinc status analyses measured as whole-body zinc concentration. After 4 and 6 months, vertebral zinc concentration was measured and serum zinc was analysed at the end of the experiment. There were no differences in growth or mortality during the experiment. The results showed a significant effect of dietary zinc supplementation level on zinc status in fish for both zinc forms. However, there were no differences in zinc status between groups given different zinc forms. In conclusion, the present experiment showed that zinc sulphate and zinc gluconate are equally efficient as zinc supplements in salmon feeds within the concentrations normally found in salmon feed.     

Use of full-fat winged bean Psophocarpus tetragonolobus seed meal as a protein feedstuff in fish-meal free diets for African catfish Clarias gariepinus

Mature winged bean Psophocarpus tetragonolobus seeds were quick-cooked and the full-fat meal derived was used to completely replace menhaden fish meal as a dietary protein source for the African catfish Clarias gariepinus . Five dry practical diets (400 g crude protein kg⁻¹ and 17.5 kJ gross energy g⁻¹ dry diet) containing menhaden fish meal (diet 1) or winged bean meal with or without graded levels of supplemental L -methionine (diets 2, 3, 4 and 5; 0, 5, 10 and 15 g kg⁻¹, respectively) were fed to catfish fingerlings (5.8  +  1.2 g) for 70 days. Weight gain, growth rate, feed conversion and protein utilization by catfish fed a winged bean meal diet without L -methionine supplementation (diet 2) was inferior ( P  > 0.05) to that in catfish fed the other diets, where performance differed nonsignificantly. Carcass protein of catfish was lower ( P  < 0.05) while liver protein was higher ( P  < 0.05) in catfish fed the winged bean meal diet without methionine supplementation. Results suggest that winged bean meal cannot replace fish meal as a protein source in catfish diets except with a minimum supplementation with 5 g L -methionine kg⁻¹ diet.     

Comparison of lipid-walled microcapsules and lipid spray beads for the delivery of water-soluble, low-molecular-weight materials to aquatic animals

Microparticles (< 40 μm diameter) composed of 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil were used to encapsulate the low-molecular-weight (mol. wt 460) antibiotic oxytetracycline in the form of either oxytetracycline hydrochloride (OTC.HCl) or oxytetracycline hemicalcium salt (OTC.HEM). Dry, finely ground particles of core material were encapsulated in spray beads. Dissolved core material was encapsulated in lipid-walled microcapsules.
Oxytetracycline (OTC) was most efficiently delivered (≈ 46.5 mg g⁻¹ lipid after 24 h suspension in seawater) as a hemicalcium salt in spray beads. Lipid-walled microcapsules were most efficient for delivering OTC (≈ 8.7 mg g⁻¹ lipid) as OTC.HCl dissolved in 0.2  M HCl at a concentration of 300 mg mL⁻¹.
Spray beads containing OTC.HEM were very stable over 1 month in storage. Lipid-walled microcapsules containing aqueous OTC.HCl lost ≈ 30% of their core material during storage. Freeze-drying of both microparticle types did not improve storage of spray beads, but showed promise for reducing leakage from lipid-walled microcapsules during storage and delivery to suspension feeders.     

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.     

Dietary vitamin C requirement of red drum Sciaenops ocellatus

A feeding trial was conducted to determine the minimum dietary vitamin C requirement of juvenile red drum and characterize signs of vitamin C deficiency. Semipurified diets containing 400 g crude protein kg^–1 from lyophilized red drum muscle and crystalline amino acids were used in the feeding trial. The basal diet without supplemental vitamin C contained ≈ 6 mg vitamin C kg^–1 and was fed for a 1-week conditioning period. Red drum, initially averaging ≈ 3.6 g each, were fed diets supplemented with 0, 10, 20, 30, 45, 60, 75, or 150 mg vitamin C kg^–1 as ascorbate polyphosphate for a period of 10 weeks. Fish fed the basal diet began to exhibit overt signs of vitamin C deficiency, including reduced weight gain, lordosis, scoliosis and loss of equilibrium after 8 weeks. Total ascorbate was undetectable in liver of fish fed the basal diet while liver ascorbate levels in fish fed the other diets generally reflected dietary supplementation. Regression analysis of weight gain data using the broken-line model resulted in a minimum vitamin C requirement ( ± SE) of 15 ± 3 mg kg^–1 diet.     

Nutrient values of dietary ascorbic acid (l-ascorbyl-2-polyphosphate) on growth, survival and stress tolerance of larval shrimp, Litopenaeus vannamei

l -ascorbyl-2-polyphosphate (ApP) was used as a vitamin C source to investigate the ascorbic acid (AsA) requirements on growth performance and stress resistance of the larval white shrimp, Litopenaeus vannamei . Five isoenergetic and isonitrogenous fish meal-fish protein hydrolysate-based diets with five levels of ApP, AsA equivalent to 91.8, 188, 271, 360 and 436 mg kg⁻¹ diet were fed to triplicate groups of L. vannamei (mean initial wet weight 1 mg) for 32 days. The diet with AsA 91.8 mg kg⁻¹ showed high cumulative mortality after 10 days of feeding. After the 32-day trial, the shrimp that fed the diet had significantly lower survival and weight gain (WG, %) than those that fed 188, 271, 360 and 436 mg AsA kg⁻¹ diets. Specific growth rate (SGR, % day⁻¹) and final body wet weight (FBW, mg) showed the same pattern as WG (%). There were no significant differences in growth performance (FBW, WG and SGR) among the groups that fed 188, 271, 360 and 436 mg kg⁻¹ of AsA at the termination of feeding trial. Broken-line regression analysis on WG indicated that 191 mg AsA kg⁻¹ in the diet was the optimum for larval L. vannamei . On the contrary, dietary level of more than 360 mg AsA kg⁻¹ was needed to ensure high resistance to stressful conditions such as low dissolved oxygen stressors.     

Growth, haematological parameters and tissue lipid peroxidation of soft-shelled turtles, Pelodiscus sinensis, fed diets supplemented with different levels of ferrous sulphate

Soft-shelled turtles, Pelodiscus sinensis , with an average weight of 5.55 g, were fed diets supplemented with eight levels of ferrous sulphate for 8 weeks. The analysed iron content ranged from 50.8 to 482.9 mg kg⁻¹. Growth rate of turtles fed the control diet with no iron supplementation was the lowest among all dietary groups. Haematological parameters including red blood cell, haemoglobin, haematocrit, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration of the turtles fed the control diet were also significantly ( P  < 0.05) lower relative to the other groups. Thus, dietary iron at 50.8 mg kg⁻¹ (no supplemented iron) was deemed deficient for growth and ineffective at preventing anaemia in juvenile soft-shelled turtle. Whereas, a supplementation of 50 mg kg⁻¹ ferrous sulphate (a total dietary iron of 91.8 mg kg⁻¹) was enough to normalize the haematological values of soft-shelled turtles to the level similar to other iron supplement-fed groups. Within the tested dietary iron range, liver iron content curve-linearly ( r ² = 0.99) increased with increasing dietary iron level. Furthermore, thiobarbituric acid-reactive substances in liver tissues of the turtles have also increased when liver iron content increased. The dietary iron requirement of soft-shelled turtle is 120–198 mg kg⁻¹ when ferrous sulphate is used as the source of iron.     

Dietary pyridoxine requirement of juvenile Jian carp (Cyprinus carpio var. Jian)

In a 80-day feeding trial, a total of 1050 juvenile Jian carp ( Cyprinus carpio var. Jian) with an average initial weight of 10.71 ± 0.05 g were fed semi-purified diets containing seven graded levels of pyridoxine (0.20, 1.71, 3.23, 4.96, 6.32, 8.58 and 12.39 mg pyridoxine kg⁻¹ diet). Results indicated that with increasing dietary pyridoxine levels up to 4.96 mg kg⁻¹ diet, percent weight gain (PWG) and specific growth rate (SGR) were improved, and no differences were found with further increase of pyridoxine levels. Feed intake also followed the similar pattern to that observed with PWG and SGR when dietary pyridoxine levels were ≤6.32 mg kg⁻¹ diet. But feed efficiency and protein efficiency ratio were not affected by pyridoxine levels. Crude protein of carcass, productive protein value and plasma ammonia concentration were improved with increasing dietary pyridoxine levels up to 4.96 mg kg⁻¹ diet. Amylase activities in the intestine were improved with increasing dietary pyridoxine levels up to 4.96 mg kg⁻¹ diet, but protease and lipase activities in the intestine were not affected by pyridoxine levels. Na⁺, K⁺-ATPase and Gamma-glutamyl transpeptidase activities in proximal intestine, mid intestine (MI) and distal intestine (DI) were lowest when fed the diet containing 1.71 mg pyridoxine kg⁻¹ diet. The alkaline phosphatase activities in MI and DI followed the same pattern. The dietary pyridoxine requirement of juvenile Jian carp based on PWG estimated by broken line model was 6.07 mg pyridoxine kg⁻¹ diet.     

Myo-inositol prevents oxidative damage, inhibits oxygen radical generation and increases antioxidant enzyme activities of juvenile Jian carp (Cyprinus carpio var. Jian)

This study was conducted to evaluate the effects of dietary myo -inositol (MI) on the antioxidant status of juvenile Jian carp ( Cyprinus carpio var. Jian). A total of 1050 Jian carp (22.28±0.07 g) were randomly distributed into seven groups of three replicates each, feeding diets containing graded levels of MI (163.5, 232.7, 384.2, 535.8, 687.3, 838.8 and 990.3 mg kg⁻¹ diet) for 60 days. Results indicated that the malondialdehyde content was the lowest for fish fed diets containing ≥384.2 mg MI kg⁻¹, and the highest for fish fed the MI-unsupplemented basal diet ( P <0.05). The protein carbonyl content was decreased with increasing dietary MI levels up to 535.8 mg kg⁻¹ diet, and no differences were found with a further increase in the MI concentration. The anti-superoxide anion capacity (ASA) and anti-hydroxyl radical capacity (AHR) were increased with increasing MI levels up to 535.8 mg kg⁻¹ diet, and plateaued thereafter. The superoxide dismutase and glutathione- S -transferase activities showed the same tendency with the ASA capacity. Catalase, glutathione peroxidase and glutathione reducase activities were improved with increasing MI levels up to 838.8, 384.2 and 687.3 mg kg⁻¹ diet, respectively, and remained nearly constant thereafter. These results suggested that MI could inhibit oxygen radical generation, increase enzymatic antioxidant capacity and prevent oxidative damage of carp. Dietary MI requirements for ASA and AHR activities of juvenile Jian carp were 567.94 and 517.22 mg MI kg⁻¹ diet respectively.     

The effect of three carotenoid sources on growth and pigmentation of juvenile freshwater crayfish Cherax quadricarinatus

The effect of adding carotenoids from various sources to feed of juvenile freshwater crayfish Cherax quadricarinatus on pigmentation, growth and survival was examined under laboratory conditions. Juvenile crayfish were fed diets fortified with carotenoids at a level of 100 μg g⁻¹ for a period of either 49 or 55 days. Carotenoid sources were: dried algal cells prepared from Dunaliella salina in which the main carotenoid is β-carotene; a synthetic carotenoid, astaxanthin (Carophyll Pink 8%, manufactured by Hoffman–La Roche) and alfalfa meal. Crayfish receiving feeds fortified with carotenoids exhibited better body colouration than those in the control group, which were fed a diet to which no carotenoids were added. Growth and survival of the crayfish were not affected by the addition of carotenoids to their diet.     

The influence of dietary phospholipid level on the performances of juvenile amberjack, Seriola dumerili, fed non-fishmeal diets

The objective of the present study was to investigate the effect of dietary phospholipid (PL) level on growth and feed intake of juvenile amberjack ( Seriola dumerili ) fed non-fishmeal (non-FM) diet containing alternative protein sources; soybean protein isolate, tuna muscle by-product powder and krill meal. Three non-FM diets were prepared to contain three levels (14, 37 and 54 g kg⁻¹ dry diet) of PL (soybean lecithin acetone insoluble, 886 g kg⁻¹) and growth performance was monitored in a 30-day growth trial by using 2.6 g of fish. The results indicated that final body weight, weight gain and feed intake significantly increased with increasing dietary PL level. At the highest dietary PL level (54 g kg⁻¹ dry diet), the fish consumed 14.8% and 10.2% as much feed as those fish fed diets containing 14 g kg⁻¹ dry diet and 37 g kg⁻¹ dry diet PL, respectively. An increasing tendency with increasing dietary PL level on feed efficiency was observed. In conclusion, the present study demonstrated that dietary PL supplementation could increase feed intake, and improve the growth of juvenile S. dumerili fed non-FM diets. Therefore, purified PL might be a good candidate to stimulate the growth of fish through enhancing the feed intake when they are fed diets containing alternative protein sources.     

Dietary vitamin E requirement of the red drum Sciaenops ocellatus

A 12-week feeding trial was conducted to establish the minimum dietary vitamin E requirement of juvenile red drum by broken-line regression analysis. The semi-purified basal diet was supplemented with 10, 20, 30, 40, 60 or 80 IU vitamin E kg⁻¹ as all-rac -α-tocopheryl acetate. Juvenile red drum were conditioned by feeding the basal diet for 8 weeks prior to the feeding trial to reduce whole-body vitamin E levels. Then, fish initially averaging 12.2 ± 0.4 g fish⁻¹ (mean ± SD) were fed the experimental diets at a rate approaching apparent satiation for 12 weeks. Weight gain and feed efficiency responses of fish fed diets were significantly ( P  < 0.01) altered by the level of vitamin E supplementation but not strictly in a dose-dependent manner. Vitamin E concentrations in liver and plasma also were significantly ( P  < 0.001) influenced by dietary vitamin E level. Plasma ascorbic acid in fish fed the basal diet tended ( P  = 0.066) to be lower than in fish fed diets containing the various levels of vitamin E. In addition, fish fed the basal diet showed edema in the heart, while fish fed all other diets were normal. Fish fed 60 or 80 IU all-rac -α-tocopheryl acetate kg⁻¹ diet had significantly higher respiratory burst of head kidney macrophages than fish fed all other diets, although dietary effects on hematocrit and neutrophil oxidative radical production were not significant. The minimum dietary vitamin E requirement of juvenile red drum was established based on broken-line regression of liver thiobarbituric acid reactive substances to be 31 mg all-rac -α-tocopheryl acetate kg⁻¹ diet.     

Effect of the protein/energy ratio on the growth of Mediterranean yellowtail (Seriola dumerili)

Yellowtails weighing 490 g were fed five experimental diets with different protein/energy ratios, 24.6, 26.9, 28.9, 31.8 and 35.8 g MJ⁻¹, for 152 days. The energy content was similar in all the diets and the protein and lipid levels were 40/26, 45/26, 50/18, 50/26 and 55/18 %CP/%CL respectively. The final weight and SGR were lower in fish fed diets with a lower PD/ED ratio (24.6 and 26.9 g MJ⁻¹), and the mortality of fish fed diet 24.6 g MJ⁻¹ was higher. In fact, only fish that consumed diet 35.8 g MJ⁻¹ had a haematocrit and a normal erythrocyte number similar to that in healthy yellowtail. No differences appeared in feed intake and feed conversion ratio. Digestible energy ingestion was similar for all the diets and digestible protein intake was also low for 24.6 compared with 35.8 g MJ⁻¹. The meat composition was similar for fish fed all the diets, but the profiles of muscle fatty acids indicated an increasing content of saturates and n-3 HUFA, while the levels of monounsaturates decreased, corresponding to an increase in the PD/ED relation. The economic conversion ratio and economic profit index were not different for fish fed the experimental diets.