Improving the fitness of Holothuria arguinensis larvae through different microalgae diets

Development and design of adequate feeding protocols on sea cucumber larvae are necessary for improvements on larvae growth, survival and production of competent juveniles. This work assessed the Holothuria arguinensis larvae growth and survival, fed with three different single microalgae diets of Chaetoceros calcitrans, Isochrysis galbana and Tetraselmis chui, and two microalgae diets based on a combination of C. calcitrans and T. chuii (C:T; 1:1) and C. calcitrans, T. chuii and I. galbana (C:T:I; 1:1:1) during 2 months. Holothuria arguinensis larvae fed with T:C:I, showed higher survival and larger larval and stomach sizes than the ones fed with the other diets. Comparing the results obtained from the single diets, H. arguinensis larvae fed with I. galbana grew and survived better during the first 5 days. However, higher growth was obtained on the larvae fed with C. calcitrans from day 5 to day 12; since this day, larvae fed with T. chuii showed the largest size. These results could be related to the different microalgae size and morphology, in addition to the nutritional value of the different microalgae used. However, no competent larvae that metamorphosed into doliolaria were obtained during this experiment. The tanks used were transparent, which could be causing light stress to the larvae, since competent larvae were obtained in opaque production tanks in our aquaculture installations during the same time period. The combined diet of C. calcitrans, T. chuii and I. galbana (C:T:I) could improve the growth and larvae competency of H. arguinensis.     

Evaluation of the optimum dietary protein level for the maximum growth of juvenile beluga (Huso huso L.1758)

A 10‐week feeding trial was carried out to evaluate the optimum dietary protein level for the maximum growth of juvenile beluga, Huso huso. Fish averaging 1.34 ± 0.07 g (mean ± SD) was randomly distributed into 18 circular fibreglass tanks of 500 L capacity (20 fish per tank). Six iso‐caloric diets were formulated to contain 30 (CP₃₀), 35 (CP₃₅), 40 (CP₄₀), 45 (CP₄₅), 50 (CP₅₀) and 55% (CP₅₅) crude protein (CP). Fish were fed each of the six experimental diets in triplicate groups. At the end of feeding trial, weight gain (WG) and specific growth rate (SGR) in fish fed CP₄₀ and CP₄₅ diets were significantly higher than those of fish fed CP₃₀, CP₃₅, CP₅₀ and CP₅₅ diets (P < 0.05). Lipid retention increased significantly from 24.7% to 31.6%, but protein retention decreased from 54.6% to 35.6% with increasing protein levels from 30% to 50%. Muscle total essential and non‐essential amino acid (EAA & NEAA) concentrations increased with the dietary protein level up to CP₄₅ diets. Muscle total EAA concentrations (%) of fish fed CP₄₅ were significantly higher than those of fish fed CP₃₀, CP₃₅, CP₅₀ and CP₅₅, but there was no significantly different between those of fish fed CP₄₀ and CP₄₅. Muscle total NEAA concentration (%) of fish fed CP₄₅ were significantly higher than those of fish fed CP₃₀ and CP₃₅ diets. Broken‐line analysis of WG suggested that the optimum dietary protein level could be 38.9% for maximum growth performance in juvenile beluga (1.3–77 g).     

Does space matter? Optimizing stocking density of Holothuria arguinensis and Holothuria mammata

Stocking density is an important factor affecting growth in aquaculture. The main objectives of this study are to evaluate the effects of different stocking densities on Holothuria arguinensis and Holothuria mammata's growth and determine the optimal density. Four different stocking densities were selected for H. arguinensis (1, 3, 5 and 7 ind/0.2 m²) and three for H. mammata (6, 10 and 12 ind/0.5 m²). Growth (specific growth rate (SGR) and growth rate (GR)), weight change, coefficient of variation and productivity were estimated, additionally the feeding rate on H. mammata. Growth on H. arguinensis decreased as the stocking density increased, showing the higher growth at the stocking density of 1 ind/0.2 m² (SGR: 1.24%/day ± 0.16 and GR: 0.94 g/day ± 0.05), with a 104.65% (±9.98) of weight change. The best H. mammata growth was registered at 10 ind/m² (SGR: 0.56% ± 0.04%/day and GR: 0.48 ± 0.04 g/day) and 25.48% (±1.52) of weight change. H. mammata feeding rate decreased as stocking density increased. Crowding stress could be considered the main factor affecting the sea cucumbers growth and performance on our study. The optimal stocking density for H. arguinensis and H. mammata under tank‐based conditions were established as 1 ind/0.2 m² and 5 ind/0.5 m² respectively. The critic biomass for H. arguinensis (471.65 g/m²) and for H. mammata (988.11 g/m²) were reached during the experiment at the fourth and fifth weeks respectively. Therefore, to ensure and increase growth of these species under tank, their biomass should be maintained under those thresholds.     

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 performance,nutrient digestibility and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

In a 10‐week study, we evaluated the effects of replacing 20%, 40% or 60% of fishmeal (present in control diet at 300 g/kg) on a digestible protein basis with yeast Saccharomyces cerevisiae or a yeast mixture of Wickerhamomyces anomalus and S. cerevisiae on growth performance, nutrient digestibility, nutrient retention and intestinal health of rainbow trout (Oncorhynchus mykiss). Triplicate tanks with 35 rainbow trout (144.7 ± 25.1 g mean ± SEM) were fed rations of 1.5% of total biomass per tank. Replacement of 60% of fishmeal with yeast mixture resulted in lower specific growth rate of 1.0% versus 1.2%/day for other diets. Apparent digestibility coefficients for crude protein and most amino acids were highest in fish fed fishmeal‐based diet, with similar values for fish fed the diet with 20% replacement with yeast mixture. Diet with 20% replacement with yeast mixture resulted in highest phosphorus digestibility. Replacement of 60% of fishmeal with S. cerevisiae resulted in oedematous mucosal fold tips in the proximal intestine. The results of this study suggest that these yeasts can replace up to 40% of fishmeal under current inclusion levels in diets for rainbow trout without compromising growth performance, nutrient digestibility or intestinal health.     

Growth and immune response of giant freshwater prawn Macrobrachium rosenbergii (De Man) postlarvae fed diets containing Chlorella vulgaris (Beijerinck)

A 50‐day growth trial was conducted to evaluate the efficacy of Chlorella vulgaris (Beijerinck) as an ingredient in the diets of giant freshwater prawn Macrobrachium rosenbergii (De Man) postlarvae (PL30). Immune response (total haemocyte count and prophenoloxidase activity) was also assessed by subjecting postlarvae to a challenge test against Aeromonas hydrophila (Chester) for 14 days. Iso‐nitrogenous and iso‐lipidic test diets were prepared using a fishmeal‐based‐positive control diet (D0) and four basal diets with inclusion levels of 2% (D2), 4% (D4), 6% (D6) and 8% (D8) C. vulgaris. Postlarvae of M. rosenbergii were randomly stocked (mean initial body weight of 0.19 ± 0.02 g) in 30‐L tanks in three replicates per dietary treatment for evaluation of growth performance. Another set of postlarvae (mean initial body weight of 1.25 ± 0.02 g) was randomly distributed in 95‐L tanks in three replicates per dietary treatment for the assessment of immune response. Results showed that specific growth rate was significantly higher (P < 0.05) in postlarvae fed D4 and D6. Variations in values for carcass protein, lipid, moisture and ash were also evident. Postlarvae fed diets with Chlorella showed increased prophenol oxidase activity and total haemocyte counts. Moreover, survival rate after challenge with A. hydrophila was significantly increased (P < 0.05). Inclusion of C. vulgaris in diets enhanced immune response and resistance of M. rosenbergii postlarvae against A. hydrophila infection.     

Effects of water hyacinth (Eichhornia crassipes) leaf protein concentrate as soybean protein replacement in white shrimp Litopenaeus vannamei (Boone) postlarvae diet

The potential of water hyacinth leaf protein concentrate (WHLPC) as an alternative protein source to soybean meal in formulated diets for the white shrimp Litopenaeus vannamei (Boone) postlarvae, was assessed. Isonitrogenous and isolipidic diets were formulated containing 40% protein and 8% lipid. WHLPC replaced 0%, 25%, 50% and 75% of soybean meal protein in the formulated diets. Twenty postlarval Litopenaeus vannamei weighing 5.0 ± 0.00032 mg were randomly assigned to twelve 30‐L aquarium tanks and were fed experimental diets for 70 days. Results show that the overall biological performance of shrimp in terms of specific growth rate (SGR), protein efficiency ratio (PER), feed efficiency (FE) and survival in treatment receiving the 25% WHLPC replacement is comparable to that of the control diet. Replacement levels beyond 25% exhibited significant depression in terms of growth performance of the shrimp. Collectively, these findings indicate that WHLPC can replace 25% of soybean meal protein in the formulated diets of L. vannamei.     

Effect of guava Psidium guajava (L.) aqueous extract diet on growth performance,intestinal morphology,immune response and survival of Oreochromis niloticus challenged with Aeromonas hydrophila

An 84‐day feeding trial was carried out to evaluate the effects of aqueous Psidium guajava leaf extract (PGE) on growth, intestinal morphology, physiology, immune response and susceptibility of Oreochromis niloticus to Aeromonas hydrophila. Diets containing 0% (P0), 0.25% (P1), 0.50% (P2), 0.75% (P3) and 1.00% (P4) PGE were fed to triplicate groups of fish (mean weight; 1.32 ± 0.04 g) for 84 days. After the 84‐day feeding trial, test fish were injected with pathogenic A. hydrophila and then fed for 14 days. More feed were consumed in groups of fish fed PGE‐treated diets and resulted in significantly higher weight gain and feed intake. Incidentally, there was an increase in the calculated area of absorption of fish fed PGE diets, as accounted for by marginally higher villi length and width. Antioxidant and immune response were improved with PGE inclusion in diets as total protein, superoxide dismutase, glutathione peroxidase and glutathione S‐transferase significantly increased (p < 0.05) in fish fed PGE diets. Results of the challenge test with A. hydrophila revealed that the highest mortality (100%) was recorded in P0. This study revealed that inclusion of P. guajava extract in the diet of O. niloticus improved growth, nutrient utilization, immune system and survival of O. niloticus fingerlings.     

Replacement of fishmeal in cobia (<Emphasis Type="Italic">Rachycentron canadum</Emphasis>) diets using poultry by-product meal

An 8-week feeding trial was conducted to evaluate the use of local poultry by-product meal (PBM) in replacement of imported fishmeal in the diets of cobia, Rachycentron canadum. Six isolipidic (12%) and isoproteic (45%) experimental diets were formulated using PBM to replace fishmeal at 20, 40, 60, 80 and 100% dietary protein. Eleven juvenile cobia (initial mean weight of 30.7 ± 0.78 g) were randomly stocked in 300-L circular fibreglass tanks and hand-fed based on the total biomass of each tank, twice a day at 0900 h and 1500 h. The fish were group weighed at 2-week intervals to monitor their growth performance in order to adjust the feeding ratio. At the end of the feeding trial, weight gains (WGs) ranging from 221 to 322% were obtained. The specific growth rate (SGR), WG and protein efficiency ratio (PER) for fish fed with PBM-based diets were not significantly different (P > 0.05) when compared to fish fed the control diet. The best SGR was recorded for fish fed with 60PBM diet, which was significantly higher (P < 0.05) than those fed the control diet with values at 2.40 ± 0.01 and 1.97 ± 0.26%/day, respectively. The FCR of 1.83 ± 0.05 for fish fed the 60PBM diet was not significantly different (P > 0.05) when compared to those fed the control diet. The PBM source and dietary level did not significantly (P > 0.05) affect the hepatosomatic index of the fish. The results from this study suggested that PBM could replace 100% dietary fishmeal without adversely affecting the growth performance, but an optimal replacement level at approximately 60% was recommended for better growth performance and efficient feed utilization.     

Effects of dietary inclusion of yacon,ginger and blueberry on growth,body composition and challenge test of juvenile rockfish (Sebastes schlegeli) against Edwardsiella tarda

Effects of dietary inclusion of yacon, Polymnia sonchifolia (YC), ginger, Zingiber officinale (GG), and blueberry, Vaccinium ashei (BB), on growth, body composition and challenge test of rockfish against Edwardsiella tarda compared to ethoxyquin were investigated. Three hundred and sixty fish were randomly distributed into 12 flow‐through tanks. Four experimental diets were prepared: the control diet (Con) with 0.1 g/kg ethoxyquin, and YC, GG and BB diets. Each diet was assigned to triplicate tanks of fish and hand‐fed for 8 weeks. Externally normal fish after fourth and eighth weeks of feeding trial were infected with Edwardsiella tarda for challenge test. Weight gain and specific growth rate (SGR) of fish fed the YC diet were greater than those of fish fed all other diets. Feed efficiency, protein efficiency ratio and protein retention of fish fed the YC diet were higher than those of fish fed all other diets. In the both fourth and eighth weeks of infection trials, mortality of fish fed the Con diet was higher than that of fish fed all other diets. In conclusion, dietary inclusion of YC, GG and BB increased weight gain and SGR of fish. YC, GG and BB for 4 and 8 weeks lowered mortality of fish at occurrence of E. tarda.     

Effects of replacing dietary fish oil and squid liver oil with vegetable oils on the growth,tissue fatty acid profile and total carotenoids of the giant freshwater prawn, Macrobrachium rosenbergii

A feeding trial was conducted to investigate the complete substitution of either fish oil (FO) or squid liver oil (SLO) with crude palm oil (CPO), canola oil (CO) sunflower oil (SFO) or linseed oil (LO), as the sole added lipid source in diets fed to triplicate groups of giant freshwater prawn, Macrobrachium rosenbergii (initial weight = 0.42 ± 0.01 g) for 6 weeks. Prawns fed the CO or SLO diets showed significantly higher (P < 0.05) specific growth rate than those fed the FO or CPO diets. The feed conversion ratio of the prawns was significantly better when fed the CO diet, compared with the FO, CPO, SFO and LO diets. The muscle eicosapentaenoic acid content of prawns fed the vegetable oil (VO) diets were not significantly different (P > 0.05) from those fed the FO diet, although all VO‐based diets led to a significantly lower docosahexaenoic acid content compared with prawns fed the FO or SLO diet. The whole‐body total carotenoid content was significantly lower for prawns fed the SLO diet compared with prawns on the CO or CPO diets. The successful use of VO instead of marine‐based oils in prawn diets will likely reduce feeding costs associated with M. rosenbergii aquaculture.     

Effects of dietary Nutrafito Plus on growth,haemotological parameters and total ammonia‐nitrogen excretion of juvenile striped catfish Pangasianodon hypophthalmus

A feeding trial was performed to determine the effect of a commercial source of Yucca schidigera and Quillaja saponaria extracts (Nutrafito Plus^®), in practical diets, on striped catfish Pangasianodon hypophthalmus growth, feed utilization, body composition, total ammonia‐nitrogen (TAN) excretion and haematological parameters. Four experimental diets were supplemented with Nutrafito Plus^® at 0%, 0.01%, 0.02% and 0.03% (diets: control, N01, N02 and N03 respectively). Three replicate groups of striped catfish, with initial mean weight of 1.78 ± 0.05 g, were fed one of the four diets for 12 weeks. The specific growth rate (SGR) and final weight of fish fed diet N03 was significantly higher (P < 0.05) than fish fed the other dietary treatments. The growth performance of fish fed diets N01 and N02 were not significantly different compared to fish fed the control diet. Striped catfish fed diet N03 had improved feed conversion ratio (FCR), net protein utilization (NPU) and protein efficiency ratio (PER) than the control (P < 0.05). The inclusion of the high dietary level of Yucca schidigera and Quillaja saponaria, diet N03, reduced TAN compared to all groups. Dietary inclusion of Yucca schidigera and Quillaja saponaria at all levels investigated did not affect the whole body proximate composition of the striped catfish (P > 0.05). The packed cell volume (PCV) and haemoglobin level in fish fed diet N03 was significantly higher than in the fish fed the control diet. The present study demonstrates that dietary inclusion of Yucca schidigera and Quillaja saponaria induced positive effects on growth performance and haematological parameters and decreased TAN excretion in striped catfish.     

Effect of replacing dietary fish meal with silkworm (Bombyx mori L) caterpillar meal on growth and non‐specific immunity of sea cucumber Apostichopus japonicus (Selenka)

The effect of dietary substitution of silkworm (Bombyx mori L) meal (SM) for fishmeal (FM) on the growth performance and non‐specific immunity of sea cucumber (Apostichopus japonicus) (initial weight: 12.8 ± 0.16 g) was determined. Four isonitrogenous and isocaloric diets were formulated: Diet 1, which served as the control diet, contained 5% FM; Diet 2 contained 3.75% FM and 1.25% SM; Diet 3 contained 2.5% FM and 2.5% SM; and Diet 4 contained 5% SM. Other ingredients in each of the four diets were kept in the same proportion. After 8 weeks of feeding, the results showed that sea cucumbers fed Diet 2 had 18.7% increases in weight over those fed the control diet, but no significant difference was observed. No obvious difference in body wall composition was detected among the sea cucumbers fed the four different diets. Immunity analysis indicated that phagocytosis and serum alkaline phosphatase activity were not significantly (P > 0.05) affected when FM was partially or completely replaced with SM. Serum lysozyme activity of sea cucumbers fed Diet 4 showed a significant (P < 0.05) growth increase compared with those fed control diet. The results revealed that SM could be an effective substitute for FM in sea cucumber diet.     

Soy protein concentrate as a substitute for fish meal in diets for juvenile Acanthopagrus schlegelii: effects on growth,phosphorus discharge and digestive enzyme activity

The current high demand and cost of fish meal (FM) necessities the evaluation of alternative plant protein ingredients in diets of farmed marine fish. A 56‐day feeding trial was performed to study the effects of replacement of FM with soy protein concentrate (SPC) in diets of Acanthopagrus schlegelii. Diets were prepared at levels of 0%, 30%, 47.5%, 65%, 82.5% and 100% SPC, respectively, replacing FM. The results indicated no significant differences (p > .05) in % weight gain (WG) and specific growth rate of fish fed S30% to S82.5% diets compared with the control diet while, further inclusion at 100% significantly depressed growth performance. SPC inclusion and phytase supplementation significantly affected the phosphorous discharge (P‐load) showing lowest value (3.83 ± 0.53 g/kg WG) in S100% compared to control (14.79 ± 0.37 g/kg WG) and in fish fed S30% diet (13.24 ± 0.89 g/kg WG) (p < .05). The results of this study showed that FM could be substituted up to 82.5% by SPC in the diet of Acanthopagrus schlegelii fingerlings (5.53 ± 0.12 g) without any adverse effects. Phytase supplementation SPC based diets could be effective in reducing the phosphorus load in the aquatic culture environment.     

Effects of dietary astaxanthin on growth,antioxidant capacity and gene expression in Pacific white shrimp Litopenaeus vannamei

Pacific white shrimp Litopenaeus vannamei (1050 individuals with initial weight of 1.01 ± 0.001 g) were fed either control diet or one of six dietary astaxanthin (AX) concentration (25, 50, 75, 100, 125 and 150 mg kg⁻¹) diets for 56 days in 35 tanks (30 shrimp per tank). After 56 days of culture, shrimp‐fed AX125 and AX150 diets had higher (P < 0.05) weight gain, specific growth rate, total antioxidant status and lower (P < 0.05) superoxide dismutase (SOD), catalase (CAT) than shrimp fed control diet. After low dissolved oxygen stress for 1 h, survival rate of shrimp fed AX75, AX100, AX125 and AX150 diets was higher (P < 0.05) than that of shrimp fed control diet. Hypoxia inducible factor‐1α (HIF‐1α), cytosolic manganese superoxide dismutase (cMnSOD) and CAT mRNA expression levels of shrimp fed seven diets were significantly down‐regulated under hypoxia than under normoxia, but their expression levels were higher under hypoxia in shrimp fed AX‐supplemented diets than in shrimp fed control diet. About 70‐kDa heat‐shock protein (Hsp70) mRNA expression level of shrimp fed seven diets was significantly up‐regulated under hypoxia than under normoxia, but its expression level was lower under hypoxia in shrimp fed AX‐supplemented diets than in shrimp fed control diet.     

Effects of dietary administration of Macsumsuk® on growth and stress to low salinity and low dissolved oxygen in whiteleg shrimp,Litopenaeus vannamei (Boone, 1931) juveniles

An 8‐week study was conducted to explore the results of Macsumsuk^® as a feed additive on the stress tolerance and growth of Litopenaeus vannamei in 15 culture tanks of 36 L each. Three hundred shrimp averaging 0.1 ± 0.01 g were fed with five isonitrogenous (48.38 ± 0.38% CP) diets (in triplicate groups) containing kaolinite (Macsumsuk^®) at 0%, 0.3%, 0.6%, 1.2% and 2.4%, namely Mk₀, Mk_0.3, Mk_0.6, Mk_1.2 and Mk_2.4. Specific growth rate (SGR) and weight gain (WG) of shrimp fed diets Mk_1.2 and Mk_2.4 were significantly better than those of shrimp fed diet Mk₀ (p < .05). However, SGR and WG of shrimp fed diets Mk_0.6, Mk_1.2 and Mk_2.4 were not significantly different. Protein efficiency ratio (PER) and feed efficiency (FE) of shrimp fed diets Mk_1.2 and Mk_2.4 were significantly better than those of shrimp fed diets Mk₀, Mk₀.₃ and Mk_0.6. Furthermore, the survival of shrimp fed diet Mk_2.4 was significantly lower than that of shrimp fed diet Mk_0.6 (p < .05). Cumulative mortality of shrimp fed diet Mk_1.2 was significantly lower than that of shrimp fed diet Mk₀ at 1–1.5 hr post‐stress to low dissolved oxygen (from 6.1 mg/L to 2.9 mg/L) and 4–5 hr post‐stress to low salinity (from 32‰ to 1‰) (p < .05). The optimum dietary Macsumsuk^® level for juvenile L. vannamei was determined as 1.97% by the polynomial regression analysis of weight gain.     

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.     

Effects of a dietary organic acids blend and oxytetracycline on the growth,nutrient utilization and total cultivable gut microbiota of the red hybrid tilapia,Oreochromis sp., and resistance to Streptococcus agalactiae

A 20‐week feeding trial was conducted to measure growth, nutrient utilization and faecal/gut bacterial counts in triplicate groups of red hybrid tilapia, Oreochromis sp., when fed diets supplemented with 0.5% organic acids blend (OAB), 1.0% OAB, 0.5% oxytetracycline (OTC) or a control diet (no additives). At the end of the feeding trial, tilapia were challenged with Streptococcus agalactiae for 22 days. Fish fed the OTC diet had significantly higher (P < 0.05) growth than the control treatment, while growth between fish fed the OTC or OAB diets was not significantly different (P > 0.05). Phosphorus, dry matter and ash digestibility were significantly higher in the 1.0% OAB diet than the control diet. Fish fed the OAB diets had significantly lower colony‐forming units of adherent gut bacteria compared to the control or OTC treatments while those fed the 1.0% OAB diet had the lowest total faecal bacterial counts. Tilapia fed the 0.5% OTC or OAB diet had significantly higher resistance to S. agalactiae than those fed the control diet. This study indicates that dietary organic acids can potentially replace OTC as a growth promoter and antimicrobial in tilapia feeds.     

A Comparison between dietary effects of Cuminum cyminum essential oil and Cuminum cyminum essential oil,loaded with iron nanoparticles,on growth performance,immunity and antioxidant indicators of white leg shrimp (Litopenaeus vannamei)

This study evaluates the effect of dietary cumin essential oil's (CEO) and cumin essential oil's loaded iron nanoparticles (CEO‐loaded NPs) on growth performance, haematological parameters and antioxidant status of white leg shrimp. Shrimps with the initial weight of 3.38 ± 0.014 g were allocated into 15 fibreglass tanks (300 L, 60 shrimps per tank) and were fed with five experimental diets containing 0 g/kg CEO (the control diet), 5 g/kg CEO, 10 g/kg CEO, 5 g/kg CEO‐NPs and 10 g/kg CEO‐NPs for 56 days. After 56 days of culture, the shrimps fed with CEO and CEO‐loaded NPs supplemented diets showed a more significant increase in growth performance (p < .05) than in the control diet. Total haemocyte count (THC) value, large‐granule cells (LGC), hyaline cells (HC)%, superoxide dismutase (SOD) and Alkaline phosphatase (AKP) activity were significantly higher (p < .05) in the shrimps fed with CEO and CEO‐loaded NPs supplemented diets than the shrimps fed with the control diet. Glutathione peroxidase (GPX) enzyme activities along with the glucose and cholesterol concentrations significantly decreased in the shrimps fed with the CEO and CEO‐loaded NPs supplemented diets more than those fed with the control diet. The results suggest that the dietary CEO‐loaded NPs can improve the growth performance, the health status and the antioxidant capacity of L. vannamei.     

The performance of microbial flocs produced with aquaculture waste as food for Artemia

The performance of microbial flocs as food for Artemia, which were produced using waste from a recirculating aquaculture system stocking European eel (Anguilla anguilla), was investigated in an 18‐day feeding trial. Four dietary treatments were used: Chlorella only (diet 1), flocs only (diet 2), and both Chlorella and flocs offered as mixed diets in different proportions (diets 3 and 4). The survival rate of Artemia fed diets 1 and 4 were significantly higher than those fed diets 2 and 3. The survival rate of Artemia fed diet 4 was the highest among the four diets. Individual length (10.02 ± 2.44 mm) and biomass production of diet 3 (3.2 ± 0.40 g L^–1) were the highest among the four diets. The crude protein contents for Artemia fed diets 2, 3 and 4 were 591.22 ± 30.15, 580.34 ± 22.42 and 533.27 ± 34.19 g kg^–1, respectively, which were significantly higher than that of diet 1 (461.25 ± 10.33 g kg^–1). The concentrations of free amino acids and the fatty acid compositions in the four diets were equal, except for the C24:0 content. The highly unsaturated fatty acid concentration of Artemia fed diet 2 was higher than those of the other three diets. It showed that microbial flocs produced from fish waste can be used for Artemia.