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.     

The effect of plant protein‐based diets on apparent nutrient digestibility,growth response,egesta quantity,postprandial ammonia excretion rate and serum quality of Nile tilapia

The study assessed the effect of oilseed meal mixtures on the biological value, faecal matter output, ammonia excretion rates and serum biochemistry of Nile tilapia over 63 days. The experimental diets (PPB 1, PPB 2 and PPB 3) were formulated using four selected oilseed meals that were mixed in different protein proportions to contribute 80% of total dietary crude protein. In each diet, either one or two of the oilseed meals were the dominant protein contributor. A commercial tilapia feed was used as the control diet (CTRL). Sex‐reversed Nile tilapia fingerlings (35 g) were stocked at 20 fish per tank in a recirculation system and fed at 3% body weight of their respective diets. At the end of the study, ADCs of dry matter, crude lipid and ash were significantly (p < .05) lower in all the plant‐based diets compared with the control diet. Fish fed the control diet had significantly higher weight gain and SGR compared with the plant‐based diets. Egesta output was 127% higher in the plant‐based diets compared with the control diet. All dietary treatments exhibited a similar trend in changes in ammonia nitrogen. Nevertheless, serum metabolites levels indicated no significant differences among treatments. Although the PPBs did not affect ADC of protein and serum profile, fish growth was reduced while faecal output increased.     

Dietary supplementation with Bacillus subtilis LT3‐1 enhance the growth,immunity and disease resistance against Streptococcus agalactiae infection in genetically improved farmed tilapia,Oreochromis niloticus

A feeding trial was conducted to investigate the effect of different levels of Bacillus subtilis LT3‐1 in diets on growth, immune parameters, intestinal morphology and disease resistance in genetically improved farmed tilapia, Oreochromis niloticus. Fish (46.91 ± 0.17 g) were fed with a basal diet supplemented with B. subtilis LT3‐1 at 0 (B0), 3.8 × 10¹⁰ (B1), 7.6 × 10¹⁰ (B2), 1.14 × 10¹¹ (B3) and 1.52 × 10¹¹ (B4) CFU kg^?1 for 6 weeks. The results showed that the weight gain of fish in B1 group was significantly enhanced compared to that in B0 group (p < 0.05). The addition of B. subtilis significantly affected serum biochemical indices (total protein, albumin, aspartate aminotransferase, alkaline phosphatase). Besides, the haematocrit, total counts of red and white blood cells, as well as the serum catalase and lysozyme activities, were increased, whereas the serum malondialdehyde, the serum immunoglobulin M and complement three contents were reduced. Parameters for intestinal morphology suggested a healthier intestine for the fish fed B. subtilis‐supplemented diets than fish fed the control diet. The survival rate after Streptococcus agalactiae challenge increased in tilapia fed with B. subtilis. The present study demonstrated B. subtilis can effectively improve growth, immunological status and resistance against S. agalactiae infection in tilapia farming.     

Effects of dietary probiotic Lactobacillus plantarum and whey protein concentrate on the productive parameters,immunity response and susceptibility of Nile tilapia,Oreochromis niloticus (L.), to Aeromonas sobria infection

Immunostimulatory feed supplements have an increasingly interest in aquaculture management. Generally, an individual supplement was used in fish diets but it is expected that the use of multi‐supplements may show synergistic enhancements in fish performance, health, and immunity. Therefore, the present investigation was carried out to evaluate the use of dietary probiotic Lactobacillus plantarum and whey protein concentrate (WPC) in practical diets for Nile tilapia, Oreochromis niloticus. Hence, probiotic L. plantarum, WPC and their mixture were incorporated into a basal fish diet (300 g/kg crude protein) as follows: T1 = a basal control diet, T2 = a basal diet containing L. plantarum, T3 = a basal diet containing 1.0 g WCP/kg diet and T4, T5 or T6 = basal diets containing probiotic L. plantarum + 1.0, 2.0 or 3.0 g WCP/kg diet, respectively. Fish (15.2 ± 0.6 g) were fed on one of the tested diets up to apparent satiation twice a day for 60 days. After that, fish were intraperitoneally injected with pathogenic bacteria Aeromonas sobria and fish mortality was observed for 10 days postchallenge. Fish growth and feed intake were significantly improved by dietary probiotic L. plantarum (T2) and/or WPC (T3) over the control group (T1), and highest fish performance was observed in T5–T6 fish groups. Similarly, highest values of haematocrit, glucose, total proteins, albumin, and globulin were significantly observed in T5–T6 fish groups. Likewise, fish fed dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) showed antioxidants and immune‐stimulating activities better than the control group. Fish fed the control diet were more susceptible to A. sobria infection showing highest fish mortality (75.0%). Meanwhile, dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) enhanced significantly the fish resistance to A. sobria infection resulting in maximum values of relative percent of fish survival (73.3%–80.0%) in T5–T6 groups. The present investigation recommended the use of probiotic L. plantarum with 2.0 g WPC/kg diet to improve the growth, antioxidant, immunity responses and tolerance of Nile tilapia to A. sobria infection.     

Growth performance,lipid requirement and antioxidant capacity of juvenile Russian sturgeon Acipenser gueldenstaedti fed various levels of linoleic and linolenic acids

To evaluate the effects of dietary linoleic (LA) and linolenic acids (LN) on growth, enzyme activities to lipid addition and antioxidant capacity of the Russian sturgeon, Acipenser gueldenstaedti, 10 diets with different sources of lipid were formulated. Coconut oil in the basal diet was replaced by sunflower oil to make three diets (LA0.5 + LN0, LA1.0 + LN0 and LA2.0 + LN0) with dietary LA at 0.5%, 1.0% and 2%, by perilla oil to obtain three diets (LA0 + LN0.5, LA0 + LN1.0 and LA0 + LN2.0) with dietary LN at 0.5%, 1.0% and 2%, and by the combination of sunflower oil and perilla oil to provide three diets (LA0.25 +LN0.25, LA0.5 + LN0.5 and LA1.0 + LN1.0) containing LA and LN at 0.25, 0.50 and 1.00%. Coconut oil was used as the control diet at 10%, but without LA and LN (LA0 + LN0). After feeding for 56 days, the fish whole body, the serum and the liver of sturgeon were sampled. Fish fed LA0 +  LN0 and LA0 + LN2.0 gained lowest weight but was not significantly different from the fish fed LA0 +  LN1.0. Fish fed LA1.0 + LN1.0 gained highest weight among all groups. Feed conversion ratio was the best in fish fed LA1.0 +  LN1.0. Survival, condition factor and viscerosomatic index did not differ among treatments. Total body n‐6 fatty acids increased with the levels of n‐6. Total body n‐3 fatty acids also increased with dietary n‐3, and fish fed 2.0% LN had the highest content of total body n‐3 fatty acids among all groups. Triglyceride and cholesterol in the serum of fish fed LA1.0 +  LN1.0 were lowest. Fish fed LA1.0 +  LN1.0 showed the highest lipoprotein lipase and lipase activities, but the lowest malate dehydrogenase activity. Fish fed LA1.0 +  LN1.0 showed higher catalase, superoxide dismutase activity and total antioxidant capacity than fish fed other diets. This study indicates that diets containing both LA and LN are best for the growth of Russian sturgeon. The level of LA1.0 + LN1.0 in the diet is most beneficial for growth performance and antioxidant capacity in juvenile Russian sturgeon.     

Dietary Oil Sources on the Innate Immunity and Resistance of Nile Tilapia,Oreochromis niloticus,to Streptococcus agalactiae Challenge

The effect of different dietary oil sources on the innate immunity and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus agalactiae infection were evaluated. Fish were fed with diets containing different lipid sources (soybean oil [SO], corn oil, linseed oil [LO], fish oil [FO], and olive oil [OO]). Fish fed SO presented the highest (P < 0.05) hematocrit and serum protein. LO and FO diets increased (P < 0.05) the erythrocyte resistance to osmotic lysis in comparison with other treatments. Fish fed OO showed the highest (P < 0.05) iron‐binding capacity and the lowest serum lysozyme and bactericidal activities (P < 0.05). No difference (P > 0.05) was found between diets in alternative complement activity. Fish fed the SO diet had the highest (P < 0.05) survival rate against S. agalactiae challenge. In conclusion, diets with LO oil and FO, rich in ω‐3 fatty acids, and OO, rich in ω‐9 fatty acids, have an immunomodulatory effect in Nile tilapia juveniles. The use of SO in the Nile tilapia diet improved immune function and resistance against S. agalactiae.     

Response of Nile tilapia (Oreochromis niloticus) to diet acidification: Effect on growth performance and feed utilization

A 12-week feeding trial was undertaken to assess growth, nutrient utilization, some hematological parameters, and proximate composition of Nile tilapia (Oreochromis niloticus) fed diets supplemented with graded levels (0.5%, 1.0%, and 1.5%) of two blends of organic acids or organic salts. Seven isonitrogenous (300 g CP kg^?1) and isocaloric (19.0 MJ gross energy kg^?1) diets were formulated. The control diet (D1) contained neither added blend of organic acids nor organic salts. Three diets (D2, D3, and D4) were supplemented with 0.5%, 1.0%, and 1.5% of malic acid + oxalic acid blend (OAB), respectively. The other three diets (D5, D6, and D7) were supplemented with 0.5%, 1.5%, and 1.5% of calcium lactate + sodium acetate blend (OSB), respectively. Fingerlings (7.05 ± 0.02 g) were randomly distributed into 21 glass aquaria (160 liter), with each aquarium holding 15 fish. At the end of the feeding trial, O. niloticus offered the control diet showed lower growth and feed utilization than all those fed the organic acids or organic salts blends supplemented diets. Fish fed the diet D3 showed the highest body weight (BW), body length (BL), weight gain (WG), specific growth rate (SGR), feed intake (FI), and the best feed conversion ratio (FCR) and protein efficiency ratio (PER). Fish fed diet supplemented by 1.5% OAB (D4) showed the highest serum protein content, while control group (D1) showed the lower level of total lipids compared with the other treatments. Fish group fed the diet supplemented with 0.5% of OSB (D5) showed the highest protein and ash contents and the lowest lipid content of the whole fish body, while the control group showed the lowest protein and the highest fat content. The present observations suggest that the growth, feed utilization, and health status of juvenile O. niloticus can be enhanced with a supplementation of 1% of OAB or OSB in the diet.     

Beneficial effects on growth,haematic indicators,immune status,antioxidant function and gut health in Juvenile Nile tilapia (Oreochromis niloticus) by dietary administration of a multi‐strain probiotic

The present study was conducted to administer a commercial multi‐strain probiotic (MP), Yilibao (Bacillus velezensis:Bacillus cereus:Lactobacillus casei = 2:2:1), in Nile tilapia, Oreochromis niloticus. In terms of aerobic Bacillus spp. counts, we produced five diets containing 0, 0.34, 1.68, 3.36 and 6.72 g/kg of MP dry product (Control, T1, T2, T3, T4). Seven hundred and fifty tilapia juveniles (13.26 ± 0.01 g) distributed into 25 tanks in five replications were fed their diet for eight weeks. Results showed that fish fed T3 and T4 diets displayed significantly higher final body weight and weight gain (p < .05). Further, all MP‐treated fish exhibited remarkably decreased plasma lipid profiles (cholesterol, triglycerides) (p < .05) and fish fed T3 and T4 diets displayed significantly higher plasma myeloperoxidase activity and complement C3 content (p < .05). Additionally, fish fed T3 and T4 diets exhibited significantly promoted total antioxidant capacity, glutathione peroxidase activity, glutathione level and declined malondialdehyde content in the plasma and/or liver (p < .05). Moreover, significantly elevated chymotrypsin activity, villus height and intraepithelial lymphocytes counts were found in fish fed T3 and T4 diets (p < .05). As fish fed T3 and T4 diets surpassed the other treatments in growth, immune–antioxidative status and gut health, the recommended dose for tilapia is 3.36–6.72 g/kg.     

Interactive effects of dietary protein and live bakery yeast, Saccharomyces cerevisiae on growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection

Yeasts used as a probiotic in fish diets could stimulate fish resistance against bacterial infection and could enhance the activities of digestive enzymes in fish guts. In addition to yeast importance, dietary protein is another important part in fish diets that should be carefully optimized to meet fish requirement. It is proposed that the yeast supplementation may enhance the dietary protein turnover and reduce the protein requirement for fish. Therefore, the interactive effects of dietary protein and yeast levels on the growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection was evaluated. In the present study, ten experimental diets were formulated to contain either 35% or 45% crude protein (CP). For each protein level treatment, bakery yeast (Saccharomyces cerevisiae) was supplemented at 0.0, 0.50, 1.0, 2.0, or 5.0 g/kg diet. Fish (0.25–0.48 g) were distributed at a rate of 25 fish per 140-L aquarium. For each diet, triplicate aquaria were fed twice a day, 5 days a week for 12 weeks. Fish growth and feed utilization were significantly affected by either dietary protein or yeast levels alone, while no significant effect of their interaction was observed. The highest fish growth was obtained at 1.0–5.0 g yeast/kg diet at both protein levels; however, the fish performance at 45% CP was better than that fed on 35% CP diets. The optimum feed conversion ratio (FCR) was obtained when fish fed on 1.0–5.0 and 2.0–5.0 g yeast/kg diet at 35 and 45% CP, respectively. The cumulative fish mortality, after interperitoneal injection with A. hydrophila for 10 days, and bactericidal activity was significantly higher in fish fed 35% CP diets than those fed 45% CP diets. Both variables decreased significantly with the increase in yeast levels. The lowest bacterial count and bactericidal activity were obtained in fish fed 5.0 g yeast/kg diet irrespective to dietary protein levels. It could be concluded that the inclusion of live bakery yeast in practical diets could improve the growth performances, feed utilization, and physiological status of Nile tilapia fry and their challenge against A. hydrophila infection. Moreover, fish performance when fed 45% CP diet was better than those fed 35% CP diet. Based on these results, the most suitable yeast level for maximum Nile tilapia growth was determined to be 2.0 g yeast/kg diet with 45% CP diet; however, this level was recommended to stimulate their productive performance and enhances their resistance against A. hydrophila infection.     

Effect of Lactobacillus acidophilussupplementation on growth performances,digestive enzyme activities and gut histomorphology of striped catfish (Pangasianodon hypophthalmusSauvage, 1878) juveniles

The influence of dietary supplementation of Lactobacillus acidophilus, on growth performance, digestive enzyme activities, gut histomorphology and gut microflora were evaluated in juveniles striped catfish (Pangasianodon hypophthalmus). Five experimental diets were formulated by supplementing 0, 10³, 10⁵, 10⁷ and 10⁹ CFU/g L. acidophilus in fishmeal and casein‐based semi‐purified diet. Triplicate groups of striped catfish (21.69 ± 0.18 g) were stocked in 15 fiberglass tanks with stocking density of 25 individuals per tank and fed twice daily at 2.5% of the fish body weight for 12 weeks. Weight gain, specific growth rate, feed conversion ratio and the protein efficiency ratio were significantly higher in fish fed with 10⁵ and 10⁷CFU/g L. acidophilussupplemented diets compared with the other treatment groups. Compared with the control and fish fed low (10³ CFU/g) L. acidophilus supplementation, those fed with 10⁵ and 10⁷ CFU/g had significantly higher (p < 0.05) apparent protein digestibility. Inclusion of L. acidophilus at 10⁷ CFU/g diet significantly increased amylase, protease and lipase activities. Microscopic analysis showed that the villi length in both the anterior and posterior gut and microvilli length in the posterior gut increased significantly in fish fed L. acidophilus supplementation at 10⁵ and 10⁷ CFU/g of diet. The fish fed L. acidophilus supplemented diets significantly increased the total lactic acid bacteria counts in the gut of striped catfish compared with the control‐fed group. Based on gut histomorphology and growth performance, inclusion of L. acidophilus at 10⁵ CFU/g appears to have the most positive effect on striped catfish farming.     

Effects of sodium diformate on growth performance,gut microflora,digestive enzymes and innate immunological parameters of Asian sea bass (Lates calcarifer) juveniles

This study was conducted to evaluate the effects of dietary sodium diformate (NaDF) on growth performance, gut microflora, digestive enzyme activities and immune response parameters of Asian sea bass (Lates calcarifer) juveniles. Fish with initial weight of 12.5 ± 0.4 g were fed with five experimental diets contained 0.0 (control), 5, 10.0, 15.0 and 20 g NaDF kg^?1 in triplicate for 6 weeks. Fish fed diet containing 5 g NaDF kg^?1 had significantly the highest final body weight and feed intake among different treatments. The gut total viable bacterial counts gradually decreased with increasing dietary NaDF level. Specific activity of chymotrypsin improved in fish fed diets administered with NaDF compared to the control group. Fish fed 5 g NaDF kg^?1 diet showed the highest serum lysozyme level among different treatments. The serum classical pathway activity of complement showed higher level in fish fed diets contained 5 and 10 g NaDF kg^?1 than other groups. According to break‐point regression method analysis, the optimum inclusion of dietary NaDF in L. calcarifer juveniles was estimated between 4.6 and 5.1 g/kg, when specific growth rate and feed conversion ratio were plotted against dietary NaDF levels.     

Growth,Body Fatty Acid Composition,Immune Response,and Resistance to Streptococcus iniae of Hybrid Tilapia,Oreochromis niloticus × Oreochromis aureus,Fed Diets Containing Various Levels of Linoleic and Linolenic Acids

The effects of dietary linoleic (LA) and linolenic acids (LN) on growth and immunity of all‐male hybrid tilapia, Oreochromis niloticus × Oreochromis aureus, were evaluated for 10 wk. Fish fed 0.12% LA + 0% LN had the lowest weight gain (WG) but was not significantly different from diets containing 0.5% LA or 0.40% LA + 1.0% LN. Fish fed 1% LA had the highest WG but did not differ from diets with 0.5% LA, 2.0% LA, 0.26% LA + 0.5% LN, 0.69% LA + 2.0% LN, or diets containing both LA and LN at 0.25, 0.5, and 1.0%. Feed intake, feed efficiency, and survival did not differ among treatments. Total body n‐6 fatty acids (FAs) increased with increasing dietary levels of n‐6. Total body n‐3 FAs also appeared to increase with increasing dietary n‐3 levels but peaked at 1% of diet. Dietary treatment had no effect on hematology, immune function, or survival to Streptococcus iniae. This study indicates that both LA and LN are dietary essential for growth of hybrid tilapia. Dietary LA alone can meet the essential FA requirement, and a level of 1.14% of diet is required for optimum growth.     

Effect of dietary Yucca schidigera extract on growth,total ammonia–nitrogen excretion and haematological parameters of juvenile striped catfish Pangasianodon hypophthalmus

A feeding trial with striped catfish, Pangasianodon hypophthalmus was performed to determine the effect of Yucca schidigera in practical diet on the growth, feed utilization, body composition, total ammonia–nitrogen (TAN) excretion and haematological parameters. A diet with fish meal as the main protein source without yucca extract was used as the control diet (Diet 1). Four diets were formulated with 0.075 (Diet 2), 0.1 (Diet 3) and 0.15 (Diet 4)% of yucca extract respectively. Fifteen fish per tank (initial mean weight 1.78 ± 0.05 g) were randomly allocated to 15 fibreglass tanks (80‐L) connected to a freshwater closed recirculation system (temperature 29.7 ± 1.0°C). The experimental diets were tested in triplicates for 12 weeks. The specific growth rate of fish fed Diet 4 was significantly higher when compared with fish fed Diet 1. The growth of fish fed diets Diet 2 and Diet 3 were not significantly different compared with fish fed the Diet 1. Striped catfish fed Diet 4 had significantly lower feed conversion ratio compared with fish fed Diet 1 and Diet 2 (P < 0.05).The incorporation of high level Yucca schidigera extract in the diets reduced TAN compared with Diet 1. Dietary inclusion of Yucca extract levels did not significantly affect the biometric parameters or whole body proximate composition of the striped catfish (P > 0.05). The PCV (%) in fish significantly increased with high levels of Yucca inclusion (Diet 4) compared with control diet. Fish fed Diet 4 showed significantly higher haemoglobin levels than Diet 1 (P < 0.05). The results indicate that dietary inclusion of Yucca schidigera extract is promising as a feed additive that could improve growth performance and some haematological parameters and the best Yucca schidigera level was 0.15%.     

Growth,tissue metabolites and digestive functionality in Sparus aurata juveniles fed different levels of macroalgae,Gracilaria cornea and Ulva rigida

The aim of this study was to evaluate the inclusion of two macroalgae as dietary ingredients on growth, body composition, intermediate metabolism, intestinal enzymes and gut histology of Sparus aurata juveniles. Six isocaloric and isonitrogenous diets incorporating 5%, 15% or 25% of Gracilaria cornea or Ulva rigida meal were tested against a control diet. Duplicate groups of fifteen fish (14 g) were fed the experimental diets for 70 days. Growth performance showed an inverse linear relationship with the inclusion level of Gracilaria. Feed conversion ratio increased significantly in fish fed 25% Gracilaria. Ulva presented a quadratic relationship with the lowest SGR at 15% of inclusion. Fish fed 25% Ulva exhibited significantly lower lipid content than those fed control diet. Overall, metabolites did not show differences with specimens fed control diet, except for plasmatic glucose and muscle lactate. Intestinal proteolytic activity was reduced with the macroalgae inclusion level, but all fish showed the same enzyme pattern. The histological study revealed no negative effect on liver and intestine structure by the macroalgae inclusion. The present work demonstrated that these ingredients can be used in practical diets for sea bream, but a more comprehensive research is needed to determine the optimum dietary level in a longer feeding trial.     

Effect of substituting fishmeal with corn protein concentrate on growth performance,nutrient utilization and skin coloration in red hybrid tilapia,Oreochromis sp.

The objective of this study was to evaluate the effects of fishmeal (FM) replacement with corn protein concentrate (CPC) on growth performance, nutrient utilization, gut morphology and skin coloration of red hybrid tilapia, Oreochromis sp. Five isonitrogenous (350 g/kg crude protein) and isolipidic (10 g/kg lipid) diets were formulated to contain CPC that substituted 0%, 25%, 50%, 75% or 100% FM. Diets were fed to triplicate groups of tilapia (mean initial weight, 10.33 ± 0.02 g) twice daily for 63 days. The results showed that replacing up to 50% FM in red hybrid tilapia diet with CPC did not show any significant adverse effects on growth, feed utilization, haematocrit counts, condition factor and gut morphology of tilapia (p > 0.05). However, replacing 75% or 100% FM with CPC had deleterious effects (p < 0.05). Carotenoids in CPC contributed to skin yellowness, which was significantly higher in the diet where 100% FM was replaced with CPC. Using regression analysis, the optimal substitution level of FM by CPC was estimated at 25% for percentage weight gain, 33% for FCR and 29% for protein efficiency ratio. CPC could be used as a single plant protein source to substitute up to 50% FM in red hybrid tilapia diets.     

Growth,immune response and resistance to Aeromonas hydrophila of darkbarbel catfish,Pelteobagrus vachelli (Richardson), fed diets with different linolenic acid levels

Experimental diets were formulated containing six levels of linolenic acid (0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%) and each diet was fed to darkbarbel catfish Pelteobagrus vachelli in triplicate for 84 days. Weight gain, specific growth rate and feed efficiency increased with the increasing levels of dietary linolenic acid, but were not significantly different among diets containing 1.0%, 1.5%, 2.0% and 2.5% linolenic acid. Red blood cell count and haemoglobin were significantly higher in fish fed the 1.0% linolenic acid than other diets. Lysozyme activity and immunoglobulin M content in fish fed 1.0% of linolenic acid were significantly higher compared with the other diets. Antibody titre in fish fed 1.0–2.5% linolenic acids was significantly higher than in fish fed 0 or 0.5% linolenic acid 14 days after Aeromonas hydrophila challenge. This study indicates that linolenic acid is essential to darkbarbel catfish. Two‐straight broken‐line analysis with SGR showed that a dietary level of 1.29% linolenic acid is the minimum required for adequate growth of darkbarbel catfish. Considering other measured indicators of fish performance, a level of 1.0–1.5% linolenic acid in the diet is recommended for the darkbarbel catfish.     

Natural dietary additive yellow loess as potential antibiotic replacer in Japanese eel,Anguilla japonica: Effects on growth,immune responses,serological characteristics and disease resistance against Edwardsiella tarda

The present experiment was conducted to evaluate the efficacy of an additive derived from the nature as an alternative of dietary antibiotic in Japanese eel, Anguilla japonica. Six experimental diets were formulated to contain no antibiotics or additive (yellow loess/YL) (control/CON), three graded levels of yellow loess at 5 (YL₅), 10 (YL₁₀) and 20 g/kg (YL₂₀), oxytetracycline at 5 (OTC) and amoxicillin at 10 g/kg amoxicillin (AMX) of diet. Weight gain (WG) and specific growth rate (SGR) from fish fed CON or YL₅ diets were significantly lower than those of fish fed YL₂₀ or OTC diets. Among non‐specific enzyme, lysozyme activity of fish fed YL₂₀, OTC or AMX was detected to be significantly higher than that from fish fed CON or YL₅ diets, whereas superoxide dismutase (SOD) activity of the fish fed CON was significantly lower than that for fish fed other experimental diets. Challenge test with bacteria, Edwardsiella tarda, showed improved disease resistance among the fish fed different levels of natural additive without any statistical difference from those fed antibiotics (OTC and/or AMX) supplemented diets. Therefore, these results demonstrated the potential of natural feed additive, yellow loess to replace oxytetracycline and/or amoxicillin in Japanese eel, A. japonica.     

Effects of replacing fish meal with corn gluten meal on growth,feed utilization,nitrogen and phosphorus excretion and IGF‐I gene expression of juvenile Pseudobagrus ussuriensis

Seven isonitrogenous and isolipidic diets containing fish meal (FM) protein replaced by corn gluten meal (CGM) protein at 0% (the control, C0), 10% (C10), 20% (C20), 30% (C30), 40% (C40), 50% (C50) and 60% (C60) were fed to juvenile Pseudobagrus ussuriensis for 8‐weeks to evaluate the effects of FM protein replaced by CGM protein on growth, feed utilization, nitrogen (N) and phosphorus (P) excretion and IGF‐I gene expression of juvenile P. ussuriensis. The results showed that the replacement level up to 40% did not affect the weight gain, specific growth rate (SGR), feed intake and protein efficiency ratio, whereas these parameters were depressed by further replacement level. Apparent digestibility coefficients (ADC) of dry matter, crude protein significantly decreased, but ADC of phosphorus significantly increased with increasing dietary CGM levels (p < .05). Fish fed diets with FM protein replaced by CGM protein led to an increase in nitrogen excretion, but led to a reduction in phosphorus excretion. No significant differences were observed in alpha‐amylase and lipase activities of intestine (p > .05). The lowest pepsin activity was found in C60 group. Fish fed diet C40, C50 and C60 had significantly lower serum lysozyme activity compared with fish fed diet C0 (p < .05). The lowest plasma alkaline phosphatase activity and the highest plasma alanine aminotransferase and aspartate aminotransferase activities were observed in C60 group. Fish fed diet C60 had significantly lower hepatic IGF‐I gene expression compared with fish fed diet C10 (p < .05). Broken‐line model analysis based on SGR against the CGM substitution level indicated that the appropriate replacement level was 37.7%.     

Effect of polysaccharides extracts of algae Ulva rigida on growth,antioxidant, immune response and resistance of shrimp,Litopenaeus vannamei against Photobacterium damselae

This study was carried out to investigate the effect of water‐soluble polysaccharides extract of algae Ulva rigida (WPU) as dietary supplement on growth performance, antioxidant enzyme activity, lysozyme and phenoloxidase activity, and resistance of shrimp (Litopenaeus vannamei) subjected to bacterial infection with Photobacterium damselae. Three replicate groups of shrimp (1.0 g) were fed four diets containing four levels, 0 or control, 0.5, 1 and 1.5 g/kg of WPU for 8 weeks over the growth trial. Thereafter, 30 shrimps from each dietary treatment were infected with bacteria P. damselae to evaluate disease resistance of infected shrimp. The results of this study showed that WPU was effective as a growth promoter for L. vannamei. The best growth rate was observed in shrimp fed 1.5 g/kg of WPU diet. Regarding antioxidant defences, the diets supplemented with three levels of WPU stimulated glutathione peroxidase and catalase activates in experimental shrimps. MDA content of L. vannamei‐fed diet containing WPU 1.5 and WPU 1.0 was lower than WPU 0 and WPU 0. 5 diets. Also, lysozyme and phenoloxidase activities of shrimp receiving WPU at 1.0 and 1.5 level were significantly higher than those fed WPU 0 and WPU 0.5 diets. In addition, using WPU extract in all diets decreased mortality in L. vannamei in a dose‐dependent manner after challenge with P. damselae. These results suggest that incorporation of water‐soluble polysaccharides from green algae U. rigida at 1.5 g/kg doses improves growth and antioxidant activity and enhances the immune responses in shrimp L. vannamei.     

Organic acids blend as dietary antibiotic replacer in marine fish olive flounder,Paralichthys olivaceus

The present study was conducted to evaluate the efficacy of organic acid blends as dietary antibiotic replacer in marine fish olive flounder, Paralichthys olivaceus. Fish averaging 3.5 ± 0.05 g (mean ± SD) were fed one of the four experimental diets: (1) without antibiotic or organic acid (Control/CON); (2) with antibiotic—50 mg oxytetracycline per kg body weight per day (OTC); (3) with organic acid blend A—4 g/kg diet (OA_A); and (4) with organic acid blend B—4 g/kg diet (OA_B), for 10 weeks. At the end of the experiment, total intestinal bacterial counts in fish‐fed OA_A, OA_B and OTC were significantly lower than that of fish‐fed CON diet (p < 0.05). Further, the group of fish‐fed organic acid blends (OA_A, OA_B) or antibiotic (OTC)‐supplemented diets exhibited lower intestinal Vibrio sp. counts compared with fish‐fed CON diet. Disease challenge test with bacteria Edwardsiella tarda showed significantly lower cumulative mortality rates for the group of fish‐fed OA_A, OA_B or OTC than that of fish‐fed CON diet (p < 0.05). There were no negative effects on the growth, serological characteristics and proximate composition among the group of fish‐fed different experimental diets. Therefore, the present experiment demonstrates that blends of organic acid could be a promising alternative to dietary antibiotics for the preventive and/or curative health management in marine fish olive flounder aquaculture.