Effect of taurine‐enriched diets on the Hsp expression,MAPK activation and the antioxidant defence of the European sea bass (Dicentrarchus labrax)

This study aimed to identify and characterize the cellular and metabolic response in vital organs of Dicentrarchus labrax, after feeding on soy‐based diets enriched with different taurine concentrations (T0.2, T0.5, T1.0 w/w). Molecular responses (expression of Hsp70, Hsp90, phosphorylation of p38 mitogen‐activated protein kinase‐p38MAPK and extracellular signal‐regulated kinases‐ERK1/2) were addressed. Metabolic and antioxidant capacities such as activities of citrate synthase (CS), malate and lactate dehydrogenase (MDH, L‐LDH), superoxide dismutase (SOD), catalase (CAT) and levels of thiobarbituric acid‐reactive substances (TBARS) were assessed. The most intense changes were detected in the liver and in the anterior intestine showing that taurine induces important protective biochemical mechanisms. Specifically, in the liver and the anterior intestine, Hsp and MAPK levels, as well as L‐LDH activity levels were up‐regulated under the effect of taurine diets. T diet had no major effect on the activity levels of CS, SOD and TBARS, except for MDH in the liver and catalase in the anterior intestine, where activity levels of these enzymes were increased under the effect of T0.2 and T1.0, respectively. These results may facilitate monitoring of adequate health status of farmed fish, exploiting the beneficial T effects and could assist at the formulation of aquaculture feeding strategies.     

Ocular tissue changes associated with anterior segment opacity in lumpfish (Cyclopterus lumpus L) eye

Lumpfish use their vision to hunt prey or, in the case of aquaculture, to see and eat pelleted diets. A common anterior ocular opacity abnormality designated in the literature as “cataract” described in both farmed and wild lumpfish has not yet been characterized in detail at the pathobiological level. We describe here lens tissue changes associated with cataract in cultured and domesticated lumpfish. Methodology included gross observations, ophthalmoscopy and histology. Young adult cultured animals approaching 400 days post‐hatch presented a range of anterior segment opacities associated with lenticular abnormalities observable at a histological level. Wild aged domesticated animals also displayed cataracts characterized mainly by abnormalities of the lens observed by both ophthalmoscopy and histology. Dysplastic lesions of the lens in one aged domesticated lumpfish were accompanied with both retinal and optic nerve degeneration. These novel naturally occurring anatomical changes in lumpfish present both commonalities and unique features associated with cataract in young adult cultured animals versus aged domesticated broodstock animals.     

Effect of diets containing a purified soybean trypsin inhibitor on growth performance,digestive proteases and intestinal histology in juvenile sea bream (Sparus aurata L.)

Juvenile sea bream were fed on diets containing 0.0, 2.0 or 4.0 g kg^?1 of a soybean trypsin inhibitor (SBTI) for 30 days. The growth performance, total protease activity and intestinal histology were studied after 0, 15 and 30 days of dietary treatment. No significant differences were found in the weight gain, specific growth rate (SGR) and feed conversion rate in fish fed on inhibitor‐supplemented diets when compared with those fed on an inhibitor‐free diet. Only the SGR at day 15 decreased significantly with protease inhibitor inclusion, although this effect was not observed at day 30. In relation to proteolytic activity at day 15, the total protease activity in the distal intestine decreased in fish fed on inhibitor‐supplemented diets. Zymograms of these extracts showed that the SBTI reduced the intensity of some proteolytic fractions in the distal intestine. A noticeable reduction in the protease activity of the intestinal content in fish fed on the highest level of soybean inhibitor (4.0 g kg^?1) was also observed. However, at day 30, the inhibition effect on these active bands was not detected, and the total protease activity was similar to that in fish fed on an inhibitor‐free diet. Histological examination revealed no perceptible differences in the intestinal structure between any of the diet groups. In addition, all fish were maintained under experimentation for 10 more days and fed on an inhibitor‐free diet to determine whether the possible effects caused by the protease inhibitor could be reverted. The administration of SBTI‐supplemented diets did not affect sea bream growth performance or intestine histology after 30 days, and only a decrease in the total alkaline protease activity was found at day 15.     

Using Bacillus subtilis E20‐fermented soybean meal as replacement for fish meal in the diet of orange‐spotted grouper (Epinephelus coioides,Hamilton)

The potential of Bacillus subtilis E20‐fermented soybean meal (FSBM) as a partial alternative component of fish meal (FM) in fed diets of orange‐spotted grouper (Epinephelus coioides) was evaluated in this study. An FM‐based diet and seven diets containing 10%, 20% and 30% and 10%, 20%, 30% and 40% of FM replaced by soybean meal (SBM) and FSBM, respectively, were fed to grouper for 84 days to evaluate possible substitution levels of FM by tracking growth performance, digestive enzyme activity and morphological changes in the liver and distal intestine. No significant differences in survival and muscle composition of grouper were found between controls and treatments. Growth performance and feed efficiency of fish fed diets with FM replaced by FSBM up to 30% were not significantly different from controls, whereas significantly decreased growth performance and feed efficiency occurred with diets containing >20% of SBM. Based on the feed efficiency, the maximum substituted levels of FM by SBM and FSBM in grouper diets were 18.36% and 29.32%, respectively, based on broken‐line analyses. Histopathological changes in the liver and distal intestine, and significantly lower activity levels of digestive enzymes, including pepsin in the stomach and trypsin, chymotrypsin, amylase and lipase in the distal intestine, were found in fish fed a diet containing 30% of FM replaced by SBM. However, these parameters were improved by the substitution of FSBM. It is therefore believed that FSBM has great potential to be used as a protein source in grouper diets in partial replacement of FM.     

Combined effects of dietary mannan oligosaccharides and total fish oil substitution by soybean oil on European sea bass (Dicentrarchus labrax) juvenile diets

This study evaluates the effects of dietary mannan oligosaccharides (MOS) on growth, tissue composition, fatty acid profiles and liver morphology of European sea bass (Dicentrarchus labrax) fed diets containing either soybean oil (SBO; SBOMOS) or fish oil (FO; FOMOS) as unique oil source for 8 weeks. Results showed that MOS supplementation enhanced specific growth rate, regardless of the oil source used, and that dietary oil source reduced fish length, regardless of dietary MOS supplementation. Dietary MOS favoured lipid accumulation in muscle and anterior intestine when supplemented in FO‐based diets compared to fish fed SBO diet and reduces it in liver in relation to lower hepatocyte area, particularly in fish fed SBOMOS diet. Dietary MOS favoured liver and not muscular ∑n‐3 PUFA, DHA, EPA and ARA deposition, when combined with FO but not when included in SBO‐based diets. Thus, MOS dietary supplementation favours fish performance and helps to minimize the side effects derived from high dietary SBO supplementation on liver lipid accumulation and hepatocyte vacuolization, which could be of especial interest on long‐term feeding trials; however, the effects on favoured deposition ∑n‐3 PUFA are limited to FO‐based diets.     

Intestinal histology and stereology in rainbow trout (Oncorhynchus mykiss) administrated with nanochitosan/zeolite and chitosan/zeolite composites

In previous study, the effects of synthesized chitosan/zeolite and nanochitosan/zeolite composites on rainbow trout growth, digestive enzyme activities and some biochemical parameters were shown. In this study, the effects of experimental diets based on the previous study on the rainbow trout intestinal histology and stereology were assessed: control diet (no zeolite and composite), T1 diet (14.28 g/kg zeolite), T2 diet (0.05 g/kg chitosan included in zeolite), T3 diet (0.5 g/kg chitosan included in zeolite), T4 diet (5 g/kg chitosan included in zeolite), T5 diet (0.05 g/kg nanochitosan included in zeolite), T6 diet (0.5 g/kg nanochitosan included in zeolite), T7 diet (5 g/kg nanochitosan included in zeolite). The experiment was conducted for 60 days. Results showed that supplemental diets did not have side effect on the normal structure of intestinal segments but administration of T1 and T4 diets had slight negative effects on structural maintenance in the middle part of intestine. Acidic mucin producing goblet cell percentage was also higher in nanocomposites‐administrated groups in comparison with the control group. Enhanced villus height, density and finally absorption surface area in different parts of rainbow trout intestine were mainly shown in T7 group. Meanwhile, higher thickness of tunica mascularis in different regions were noted in treatment groups especially in T7 group. The number of intraepithelial mononuclear leukocytes in fish intestine received treatment diets was also higher than control group. In conclusion, nanochitosan/zeolite composites in comparison with zeolite and chitosan/zeolite composites were more effective to improve histological structure of rainbow trout intestine.     

Pectic hydrolysates in the diet of silver catfish (Rhamdia quelen): Growth performance,blood and liver biochemistry,histological parameters and intestinal contents

The aim of this study was to investigate the prebiotic potential of pectin hydrolysates that were extracted from agroindustrial waste (apple pomace—AP and passion fruit peel—PFP) and were added to the diet of silver catfish (Rhamdia quelen). A 49‐day biological assay was conducted, and five test diets were evaluated: one diet was a control diet and the other four diets included pectin hydrolysates (2.5 and 5 g/kg). At 49 experimental days, biometric data and biological material were collected to determine the performance, plasma and liver and histological parameters and to evaluate the intestinal contents. The results were analysed by the normality test, which was followed by an analysis of the variance; the treatment means were compared by an orthogonal contrast analysis at a 5% level of significance. The inclusion of 2.5 g/kg apple pomace hydrolysates resulted in a greater production of butyric acid, increased thickness of the muscular layer and higher goblet cell count in the intestine. The inclusion of 5 g/kg apple pomace hydrolysates led to a greater concentration of liver protein. Further studies are needed to increase the knowledge about the use of these additives in the diet of silver catfish and to establish levels that allow greater gains for the species.     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.     

The effect of feeding on morphological changes in intestine of pike-perch (Sander lucioperca L.)

The pike-perch (Sander lucioperca L) at the age of 18 days were fed for 21 days with three different diets: Aglo Norse (AN), casein-gelatin (Cas), cod meal with gelatin (Mac) and nauplius Artemia salina (Art—control diet). On the last day of the experiment, fish fed Art and AN diets had the statistically significant highest body mass, length, and survival. On the last day of the experiment, pikes fed Cas diet had the lowest folds of the anterior and posterior intestine. In the anterior intestine of fish fed Cas diet was found a statistically significant increase in the proliferation of the enterocytes as compared with fish from other feeding groups. The fish from Mac-feeding group had the largest statistically significant total area of enterocytes and the absorption area of posterior intestine. This was probably the effect of disorders in the intracellular digestion and the stoppage in transportation of the intracellular digestion products into the circulatory system. Moreover, there was found the intensive processes of apoptosis of enterocytes in the fish fed Mac. On the last day of the experiment, fish fed Art and AN had statistically significantly more cells secreting cholecystokinin and gastrin (Gas) as compared with fish from other feeding groups. Results indicate that juvenile pike-perch can be reared and fed commercial diet AN since its 18th day after hatching. Feeding pike-perch Cas and Mac diets did not satisfy nutritional needs of fish, resulting in low survival, growth rate, and pathological changes in the intestine.     

Effects of nutritional status and diet composition on fatty acid transporters expression in zebrafish (Danio rerio)

This study investigated the expression of zebrafish (Danio rerio) fatty acid transporters, such as scavenger receptor CD36, plasma membrane fatty acid‐binding protein (FABPpm), and fatty acid transport protein family (FATPs), in responses to nutritional status and diet composition. For diet composition study, three isonitrogenous (43% crude protein) purified diets were formulated to contain 6%, 12% and 18% crude lipid levels. Meanwhile five isonitrogenous and isoenergetic purified diets were formulated to contain different lipid sources including fish oil (FO; rich in n‐3 HUFA), palmitic acid (PA; rich in C16:0), olive oil (OO; rich in C18:1n‐9), sunflower oil (SO; rich in C18:2n‐6) or perilla oil (PO; rich in C18:3n‐3) as the sole lipid source. Results showed that liver CD36, FABPpm‐a, FABPpm‐b, FATP1‐a and FATP6, intestine CD36, FABPpm‐a and FABPpm‐b, and muscle CD36 and FATP1‐b were significantly increased during postprandial period. During starvation, liver CD36, FABPpm‐a, FABPpm‐b and FATP1‐a, intestine FABPpm‐a, FABPpm‐b, FATP4 and FATP6, and muscle FATP1‐b, FATP4 and FATP6 were significantly increased. The expression of some fatty acid transporters (including liver CD36 and FABPpm‐b, intestine FABPpm‐a, and muscle CD36, FABPpm‐a, FATP1‐a, FATP2 and FATP4) was up‐regulated by refeeding, while the expression of other fatty acid transporters (liver FABPpm‐a and intestine FATP1‐a, FATP4 and FATP6) was down‐regulated by refeeding. The expression of several fatty acid transporters (liver FATP2 and FATP4, and intestine CD36, FATP2 and FATP4) was significantly increased by high‐lipid diet, whereas CD36, FATP1‐b, FATP2 and FATP4 expression in the muscle were reduced by increasing dietary lipid level. Compared with FO group, the muscle of fish fed the diet with OO had a higher CD36 mRNA abundance, while the muscle of fish fed the diet with OO and PO had a higher FATP1‐b expression. Compared with the FO group, the hepatic FATP2 mRNA was significantly increased in the PA group, while the intestine FATP2 mRNA was significantly increased in the SO and PO groups. In addition, intestine FATP4 expression in the PA and OO groups was lower compared with the FO group. The results indicate that zebrafish fatty acid transporters play a central role in coordinating the mobilization of fuel substrates in responses to nutritional status and diet composition.     

Nutritional regulation of intestine morphology in larval cyprinid fish, silver bream (Vimba vimba)

The present study includes the evaluation of morphological changes in the digestive tract of larval, stomachless fish silver bream ( Vimba vimba ) fed with various diets – live Artemia nauplii, commercial feed Aglo Norse (NOR) and semi-purified formulated diets: casein–gelatin (CG), dipeptide-protein (50P), dipeptide (100P), no-arginine dipeptide diet (100Pw/oArg) and a free amino acid (FAA) mixture diet. The supranuclear area of enterocytes in the posterior intestine contained enlarged absorptive vacuoles in the FAA, 100P and 100Pw/oArg groups, compared with the remaining groups. Hepatocytes' cytoplasm in fish fed with FAA, 100P and 100Pw/oArg contained mainly glycogen, and no lipid vacuoles were found. Fish fed with 100Pw/oArg showed the lowest hepatocyte surface areas while in those fed with 50P, the largest nuclei diameters were observed. Fish fed with Artemia , NOR and CG diets showed significantly ( P <0.05) higher number of proliferating cells compared with the remaining groups. Chromogranin A staining showed endocrine-immunoreactive cells (CgA-IR) in the taste buds in the oral cavity and in the enterocytes' supranuclear areas of the anterior and posterior intestine. We conclude that the growth rate and histological examination of the digestive tract in the 50P group of silver bream showed no nutritional deficiency.     

Evaluation of zinc supplementation in European sea bass (Dicentrarchus labrax) juvenile diets

This study aimed to investigate the effect of increased zinc dietary levels on the growth performance, feed utilization, immune status and induced wound healing in European sea bass (Dicentrarchus labrax). Fish weighing 10 g were fed five diets containing organic zinc at 30, 70, 110 and 150 mg kg^?1 diet and one inorganic zinc source (zinc oxide) at 150 mg kg^?1 diet for a period of 12 weeks. No significant (P>0.05) differences were found in the growth performance parameters (final weight, specific growth rate), immunological indices tested (respiratory burst activity in whole blood) and the wound‐healing process. Zinc accumulation in the skin, vertebrae and liver increased significantly (P<0.01) with increased dietary zinc levels but not in muscle. The highest zinc concentrations were obtained in skin tissue, followed by vertebrae, liver and muscle tissue. Using the concentration of zinc in skin as a response criterion, broken‐line analysis showed that the supplementation of 148 mg organic Zn kg^?1 diet seemed to be the optimum dietary zinc supplementation level for sea bass juveniles.     

Comparative effect of advanced soy products or corn protein concentrate with porcine meal on growth,body composition,and distal intestine histology of Florida pompano,Trachinotus carolinus

The present study was designed to investigate the effects of diets containing advanced soy products (enzyme‐treated soy and fermented soy) or corn protein concentrate (CPC) in combination with porcine meal (PM) to completely replace poultry byproduct meal (PBM) on growth performance, body composition, and distal intestine histology of Florida pompano, Trachinotus carolinus. Four experimental diets were formulated to be isonitrogenous and isolipidic, to contain 400 g/kg crude protein and 80 g/kg lipid. A reference diet (PBM diet [PBMD]) contained 150 g/kg PBM and 495 g/kg soybean meal (SBM), and three test diets were formulated replacing PBM with 15 g/kg of CPC (CPC diet [CPCD]) or replacing all SBM and PBM with 535 g/kg fermented soy (fermented soybean meal diet [FSBMD]) or 451.3 g/kg enzyme‐treated soy (enzyme‐treated soybean meal diet [ESBMD]). All three test diets were supplemented with 38 g/kg of PM. Diets were fed based on a percentage of bodyweight adjusted after sampling the fish every 2 weeks to triplicate groups of Florida pompano juveniles (mean weight 8.06 ± 0.22 g). After 8 weeks of feeding, fish fed CPCD and ESBMD performed equally well in terms of final body weight, thermal growth coefficient, and percentage weight gain in comparison to fish fed PBMD. In all cases, feeding FSBMD resulted in poor feed conversion and lower feed intake compared to other treatments. Protein retention efficiency, whole‐body proximate composition, phosphorus, sulfur, potassium, magnesium, calcium, sodium, and zinc contents were not significantly influenced by the dietary treatments. The results obtained in the present histological study showed no significant differences in the thickness of serous layer, muscular layer, and submucosal layer of the intestine among treatments. Fish fed CPCD showed a significant widening of the lamina propria with an increase of cellular infiltration and higher presence of goblet cells compared to other dietary treatment. Based on these results, 451 g/kg ESBM or combination of 150 g/kg of CPC and 495 g/kg SBM supplemented with 38 g/kg PM can be utilized to develop a practical diet for juvenile Florida pompano without impacting growth, nutritive parameters, and several distal intestine health parameters.     

Functional linseed fibres and their impacts on silver catfish (Rhamdia quelen) nutrition

This study was conducted with the objective of evaluating the combination of different ratios of soluble and insoluble linseed fibre for silver catfish (Rhamdia quelen). For this, the soluble and insoluble fractions were concentrated separately and combined in four ratios (1:0.5, 1:1, 1:2, 1:4), which were added to silver catfish diets and evaluated in a bioassay. After 45 days of receiving the experimental diets, the animals were submitted to biometry to collect data and tissues. The experimental design was completely randomized, with five treatments and four replications and the means were compared by Tukey's test (p < .05). Diets 1:2 and 1:4 provided higher weight gain, specific growth rate and crude protein deposition to the fish, whereas only the 1:4 diet reflected higher crude body protein. The 1:0.5 diet altered the trypsin activity in the intestine, and, together with the 1:4 diet, it provided a higher intestinal villi height. Body yield, somatic and digestive parameters, chymotrypsin activity and glucose, glycogen and liver protein were not altered, regardless of the experimental diets. In conclusion, the results indicate that linseed fibre acts effectively as a growth promoter in silver catfish diets, with the use of 1:2 and 1:4 ratios optimizing its prebiotic action.     

Dietary organic acids blend alone or in combination with an essential oil on the survival,growth, gut/liver structure and de hemato‐immunological in Nile tilapia Oreochromis niloticus

This study evaluated the effects of dietary supplementation of organic acids blend (OAB) alone or in combination with essential oil, Lippia origanoides (OAE) for Nile tilapia fed supplemented diets for 30 days. Fish (1.1 ± 0.04 g) were fed control (Control), or OAB 0.5% or OAB 0.5% + essential oil 0.125% (OAE) respectively. At the end of the experiment, samples were collected for de hemato‐immunological, histological analysis of the intestine and liver, as well as microbiology of the intestine. The pH of the diets supplemented with OAB and OAE reduced 0.92 and 0.19 respectively. The growth and FCR were unaffected by the treatments, but survival was significantly higher in the OAB treatment. Fish fed the OAB diet showed reduced concentration of total heterotrophic bacteria and Pseudomonas sp. in the intestine. Increased glucose in fish fed OAB and high number of circulating monocytes in fish fed OAE diet were observed. The anterior intestine of fish fed OAE diet showed larger number of goblet cells and increased villi height. The diet supplemented with OAB, mainly, improved the intestinal health and survival of tilapia juveniles and can be used in juvenile production.     

Influence of lupin and rapeseed meals on the integrity of digestive tract and organs in gilthead seabream (Sparus aurata L.) and goldfish (Carassius auratus L.) juveniles

Two rearing trials were conducted to evaluate the effects of dietary lupin (LM) and rapeseed (RM) meals in gilthead seabream (Sparus aurata L.) and goldfish (Carassius auratus L.) juveniles. Each plant meal was incorporated at the rate of 200 g kg^?1 in two distinct diets, which were compared with a fishmeal‐based diet as control. After 1 month, the two plant diets did not influence the whole body growth, but the digestive systems were affected. The splenosomatic index was reduced with two plant meals in goldfish and with RM in seabream. The hepatosomatic index was only reduced in LM‐fed seabream. Cellular characteristics were also affected. The largest liver cells were observed in RM‐fed goldfish suggesting changes in metabolic function. The LM and RM diets stimulated in seabream, especially the reaction in haematopoietic tissues with the proliferation of melano‐macrophages centres, and a tendency for elongated villus height in the anterior intestine thus that possibly compensated for a reduction in digestive function. Such adaptive structural modifications and the absence of degenerative signs allowed concluding that the integrity of the digestive system was maintained in fish fed plant meals.     

Partial replacement of fishmeal by defatted soybean meal in formulated diets for the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775)

This study was conducted to evaluate the effect on growth and feed efficiencies of the mangrove red snapper (Lutjanus argentimaculatus) when dietary fishmeal is partially replaced by defatted soybean meal (DSM). In the preliminary experiment, snapper (mean weight±SD, 58.22±5.28 g) were fed in triplicate with different dietary amounts of DSM (7.8–42.2%) that were formulated to be isonitrogenous and isocaloric. After 14 weeks, survival, growth and feed efficiencies, and hepatosomatic index (HSI) did not differ. Based on these results, a feeding trial was done using a positive control diet that contained 64% fishmeal, while the other four diets had DSM levels of 12%, 24%, 36%, and 48% that replaced fishmeal protein at 12.5%, 25%, 37.5%, and 50% respectively. All diets were formulated to have about the same protein level (50%), protein to energy ratio (P/E of 25‐mg protein kJ^?1), and dietary energy (19.8 MJ kg^?1). These were fed to triplicate groups of snapper (mean total weight tank^?1±SD, 73.19±1.2 g) at 15 fish (average weight, 4.88 g) per 1.5‐t tank for 19 weeks. Growth (final average weight and specific growth rate (SGR), feed conversion ratio (FCR), survival, and HSI were not significantly different (P>0.05) while protein efficiency ratios or PERs were similar in treatments with DSM. Among snapper fed DSM, haematocrit value was significantly lower in fish fed 48% DSM and not different with fish fed 36% DSM. Whole‐body crude fat of snapper fed 48% DSM was lowest while the crude protein and nitrogen‐free extract (NFE) levels were highest. Histopathological analysis showed that lipid vacuoles in livers of snapper were reduced in size as dietary DSM increased. There was slight lipid deposition in the liver of snapper at 36% DSM while at 48% DSM it was excessive and hepatocytes were necrotic. There were no differences in the histology of snapper intestine. Under the experimental condition of this study, DSM can be used in snapper diets at 24% (replacing 25% of fishmeal protein) based on growth, survival and feed efficiencies, and histology of liver and intestine. For a lesser diet cost, an inclusion level higher than 24% DSM is possible with a bioavailable phosphorus supplement.     

Feed intake, growth and nutrient utilization in Atlantic halibut (Hippoglossus hippoglossus) fed diets containing a bacterial protein meal

Triplicate groups of Atlantic halibut were fed diets containing 0%, 9% or 18% of a bacterial protein meal (BPM) produced from natural gas in a 9‐week trial. Growth rates, relative feed intake, feed efficiency ratio and retention of all indispensable amino acids were significantly lower in fish fed the 18% BPM diets than in those fed the 0% and 9% BPM diets. There were no significant treatment effects on urea levels in plasma, liver or muscle, or in uric acid levels in plasma. The hepatosomatic index was lowest in fish fed the 18% BPM diet. Although the concentration of copper, an element abundant in BPM, increased in the liver as dietary BPM level increased, the total copper content in liver decreased. Fish fed the 0% and 9% BPM diets had a higher degree of supranuclear vacuolization of pyloric caeca and mid‐intestine epithelia compared with fish fed the 18% BPM diet. In conclusion, the halibut fed the 9% BPM diet performed equally well as the control group regarding growth, feed intake and feed efficiency ratio, whereas performance was reduced in the fish fed the 18% BPM diet.     

Effect of Diets Formulated with Native Peruvian Plants on Growth and Feeding Efficiency of Red Pacu (Piaractus brachypomus) Juveniles

We evaluated the effects of casein‐based semipurified diets, alone or supplemented with native Peruvian plants, on growth, feed efficiency, and histology of the digestive tract of red pacu, Piaractus brachypomus, juveniles over an 8‐wk feeding trial. Three tanks were randomly assigned to one of four casein–gelatin (40:8) diets containing a supplement of 15% wheat meal (control) or an identical level of substitution of three South American native plant as follows: camu‐camu fruit (Myrciaria dubia), aguaje fruit (Mauritia flexuosa), or maca tuber meal (Lepidium meyenii). The fish (initial weight, 2.04 ± 0.06 g) were fed experimental diets at decreasing feeding rates from 4 to 2.6% of body weight. After 8 weeks of feeding, fish fed a diet supplemented with maca meal showed significantly higher (P < 0.05) weight gain, specific growth rate, protein efficiency ratio (PER), apparent net protein utilization (NPU), and instantaneous feed intake than fish fed other diets. Feed conversion ratio (FCR), PER, and NPU in fish fed the casein–gelatin diet supplemented with maca meal were among the best ever reported in the scientific literature, 0.64 ± 0.03, 3.13 ± 0.15 and 23.8 ± 2.0, respectively. The camu‐camu meal had a negative impact on diet palatability and utilization, which resulted in slower growth. The stomach, intestine, pancreas, and pyloric caeca at the start and end of the experiment showed normal differentiation and appearance of cells and tissues. The liver parenchyma showed lipid infiltration and pigment accumulation in all samples at the initiation of the experiment and may be attributed to the period of decreased feed intake prior to the study. At the end of the study, similar histopathologies were recorded in all samples from the control and camu‐camu groups. Normal liver histology (polyhedral hepatocytes with centrally located nuclei) was observed in two of three samples from the maca group and all the samples from the group that was fed the aguaje‐supplemented diet.     

Relative bioavailability of zinc in supplemental inorganic and organic sources for Nile tilapia Oreochromis niloticus fingerlings

A 90‐day feeding experiment was conducted with sex reversed Nile tilapia (Oreochromis niloticus) fingerlings fed purified or practical diets supplemented with different zinc sources to evaluate fish growth performance and zinc and iron retention in fish bones, fillets, liver, skin and eyes. The relative bioavailability value (RBV) of zinc in the supplemental sources tested was also calculated. Fish were fed with isonitrogenous and isoenergetic purified or practical diets supplemented with 150 mg Zn kg^?1, as zinc sulphate monohydrate (ZnSO₄), zinc oxide (ZnO) or zinc amino acid complex (Zn‐AA). The feeding trial was conducted in 30, 50 L aquaria where four 0.66 ± 0.01 g (mean ± SD) fingerlings were initially stocked. No significant differences were observed for any growth performance variables (P > 0.05). In practical diets, only ZnSO₄ and ZnO presented bone zinc retention similar to that for the standard zinc source. Zinc concentration in the bone of fish fed practical diet supplemented with Zn‐AA (171 ± 3.62 μg g^?1) was significantly lower than that verified for the practical diets supplemented with the standard zinc source (200 ± 17.7 μg g^?1) or with ZnSO₄ (204 ± 19.9 μg g^?1). Assuming the concentration of zinc in bones as the response criterion, the supplemental zinc RBV from ZnSO₄ (105%) was higher than the RBV for Zn‐AA (95.1%) or ZnO (94.9%). Iron concentration in the bones of animals fed the non‐zinc‐supplemented purified diet was significantly higher than that observed for purified diet supplemented with Zn‐AA (P < 0,05). The results of the present work allowed us to conclude that ZnSO₄ in relation to ZnO or Zn‐AA was the supplemental zinc source with higher zinc bioavailability to Nile tilapia.