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.     

Aeromonas jandaei and Aeromonas veronii caused disease and mortality in Nile tilapia,Oreochromis niloticus (L.)

Diseases caused by motile aeromonads in freshwater fish have been generally assumed to be linked with mainly Aeromonas hydrophila while other species were probably overlooked. Here, we identified two isolates of non‐A. hydrophila recovered from Nile tilapia exhibiting disease and mortality after exposed to transport‐induced stress and subsequently confirmed their virulence in artificial infection. The bacterial isolates were identified as Aeromonas jandaei and Aeromonas veronii based on phenotypic features and homology of 16S rDNA. Experimental infection revealed that the high dose of A. jandaei (3.7 × 10⁶ CFU fish^?1) and A. veronii (8.9 × 10⁶ CFU fish^?1) killed 100% of experimental fish within 24 h, while a 10‐fold reduction dose killed 70% and 50% of fish, respectively. When the challenge dose was reduced 100‐fold, mortality of the fish exposed to A. jandaei and A. veronii decreased to 20% and 10%, respectively. The survivors from the latter dose administration were rechallenged with respective bacterial species. Lower mortality of rechallenged fish (0%–12.5%) compared to the control groups receiving a primary infection (37.5%) suggested that the survivors after primary infection were able to resist secondary infection. Fish exposed to either A. jandaei or A. veronii exhibited similar clinical signs and histological manifestation.     

Dietary taurine improves reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock

This study was conducted to evaluate the effects of supplemental taurine on reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock fed soybean meal‐based diets. Four isonitrogenous (350 g kg^?1 protein), isocaloric (18 MJ kg^?1) diets were formulated to contain 0, 5, 10 and 15 g kg^?1 taurine. The diets were fed to triplicate groups of juvenile Nile tilapia (10–15 g average body weight) at a female: male ratio of 3 : 1, to apparent satiation, three times per day for 130 days. The size at first maturation decreased with increasing dietary taurine to 10 g kg^?1 and levelled off with further taurine supplementation. The time to first spawning was also significantly shorter at 10 g kg^?1 taurine level. Spawning performances, including spawning frequencies, total number of spawnings per tank, number of spawnings per female and absolute fecundity, were all significantly improved with increasing dietary taurine up to 10 g kg^?1. However, the quadratic regression analyses indicated that the maximum spawning performance occurred at 8 g kg^?1 of supplemental taurine. Eggs produced from broodstock fed 10 g kg^?1 taurine exhibited significantly higher hatchability and required shorter time for hatching and yolk‐sac absorption and also resulted in higher larval weight than at other dietary taurine levels. The highest egg protein, total amino acids and taurine were also obtained at 10 g kg^?1 taurine. These results suggest that 8 g kg^?1 dietary taurine is required for optimum reproductive outputs of Nile tilapia broodstock.     

In vivo and in vitro assessment of Lactobacillus acidophilus as probiotic for tilapia (Oreochromis niloticus,Perciformes:Cichlidae) culture improvement

In this study, the use of Lactobacillus acidophilus as a probiotic for Nile tilapia (Oreochromis niloticus) culture was studied. Fish survival and the expression of some genes involved in the immune response were assessed. Diet supplementation with L. acidophilus for 15 days caused a significant increase in fish survival during a challenge with Aeromonas hydrophila and variations in immune response related to IL‐1β and transferrin expression in Nile tilapia spleen and kidney. Moreover, extracellular products (ECPs) of L. acidophilus showed high antibacterial activity against fish pathogens such as A. hydrophila and Streptococcus agalactiae in vitro. It was also observed that viable L. acidophilus was able to disrupt quorum sensing activity in Chromobacterium violaceum.     

Effects of dietary supplementation of a marine thermotolerant bacterium,Bacillus paralicheniformis SO‐1, on growth performance and immune responses of Nile tilapia,Oreochromis niloticus

This study was carried out to evaluate the effects of dietary supplementation of thermotolerant bacterium on growth and immune responses of Nile tilapia (Oreochromis niloticus). Bacillus paralicheniformis SO‐1 was isolated from marine environments and incorporated into four isonitrogenous (300g/kg crude protein; cp) and isocaloric (18 MJ/kg) diets at four concentrations: 0, 5, 10 and 20 g/kg diet. Each diet was fed to triplicate groups of Nile tilapia (41.5 ± 0.5 g average weight) at a daily rate of 3% of their biomass, three times a day for 50 days. At the end of the feeding trial, the growth rates, feed utilization efficiency (feed conversion ratio, protein efficiency ratio, protein productive value), digestive enzymes (protease, amylase and lipase) activities, immunological response (serum lysozyme activity, phagocytic activity, respiratory burst and superoxide dismutase activity) and the expression of immune‐related genes [interleukin‐1 (IL‐1), interleukin‐4 (IL‐4) and interleukin‐12 (IL‐12)] were determined. Growth rates, digestive enzymes activities and immunological parameters were significantly improved (p < 0.05) with increasing supplemental SO‐1 up to 10 g/kg. However, further increase in bacterial concentration to 20 g/kg lead to significant decline in fish performance and immune response (p < 0.05). The expression of IL‐1, IL‐4 and IL‐12 genes was significantly up‐regulated (p < 0.05) in the liver of Nile tilapia fed SO‐1‐treated diets. This study clearly demonstrated that B. paralicheniformis SO‐1 could be considered as an efficient growth promoter and immune‐stimulating probiotic for farmed Nile tilapia.     

Selection response for Streptococcus agalactiae resistance in Nile tilapia Oreochromis niloticus

The potential of selection to improve resistance to streptococcosis was evaluated in a commercial population of Nile tilapia in Thailand. The base generation (G0) consisted of offspring from 98 sires and 149 dams using a partly nested design. At 60 days post‐hatch, 30 fish from each family were injected intraperitoneally with a Streptococcosis agalactiae solution (1 × 10⁹ CFU/ml) and evaluated for 14 days. Disease resistance was recorded as the number of days from challenge until death (DD) and as a binary (BIN) trait (dead/alive) on day 14. Three models were used for genetic analyses: Cox frailty model for DD; animal model for DD; and animal model for BIN. Age at challenge was fitted as a covariate and contemporary group as fixed or random effect, depending on the model. Fish from the 18 most resistant families were selected to produce the first generation (G1). Heritability estimates for G0 were 0.22, 0.14 ± 0.02 and 0.11 ± 0.02 for the Cox, linear DD and linear BIN models, respectively. Selection response indicated that the risk of death decreased to 54%, survival time increased to 3.4 days and survival rate increased to 21%. These results suggest that genetic improvement is possible for this population.     

Dietary Aspilia mossambicensis and Azadirachta indica supplementation alter gonadal characteristics and histology of juvenile Nile tilapia (Oreochromis niloticus)

The use of medicinal plants to control reproduction in aquaculture have recently received considerable attention because they are biodegradable, safe, effective and locally available. However, information on their effects on gonadal characteristics and histological features in fish is currently limited. The present study evaluated the gonadal characteristics and histological changes of Nile tilapia, Oreochromis niloticus gonads fed on Aspilia plant, Aspilia mossambicensis and Neem tree, Azadirachta indica. Juvenile fish were fed diets supplemented with four doses (1.0, 2.0, 4.0 and 8.0 g/kg diet) of A. mossambicensis or A. indica leaf powders at 3% of their body weight daily for 90 days to examine absolute fecundity (AF), relative fecundity, gonadosomatic index (GSI) and histology of gonads. The antifertility phytocompounds in the two plants were quantified by using standard methods. Results indicated that, all doses of A. indica and A. mossambicensis used reduced significantly AF and GSI values (p < 0.05). Dose‐dependent histological alterations of gonads were noticed in both plants starting from doses of 2.0 g/kg in males and 4.0 g/kg in females. The highest percentages of total flavonoids (23.7%) and alkaloids (14.2%) were obtained from A. indica ethanol extract (p < 0.05). Taken together, dietary supplementation with A. mossambicensis and A. indica leaf powders alter gonadal characteristics of O. niloticus and histology triggered by alkaloids and flavonoids. Farmers interested in using the two plants to control prolific breeding should limit the dose inclusion to 2 g/kg to avoid severe effects on fish testis and ovaries.     

Dietary supplementation of Tribulus terrestris extract improves growth and reproductive performances of the male Nile tilapia (Oreochromis niloticus)

Effects of dietary supplementation of Tribulus terrestris (TT) and 17α‐methyl testosterone (MT) on growth performance and reproductive efficiency of male Nile tilapia, Oreochromis niloticus (N = 75, initial weight 60 ± 3.251 g), were evaluated. Five experimental treatments in triplicate were fed on basal diet (30% crude protein) (control group, CG), basal diet containing 60 mg MT (MT group) and basal diet containing 250, 500 and 750 mg/kg diet TT (TT250, TT500 and TT750 groups), respectively, for consecutive 45 days. Results revealed that the fish received TT in diet showed better growth performance (final body weight, weight gain, feed conversion ratio, specific growth rate, testes weight and gonadosomatic index) compared with MT and CG (p < .05), as well as for haemoglobin content and red blood cell count (p < .05). The highest level of testosterone, 11‐keto testosterone, sperm concentration and vitality was recorded in TT750 followed by TT500, TT250 and MT groups, while the lowest value was recorded in the CG (p < .05). The highest seminiferous tubule diameter was recorded in TT750 followed by TT500, TT250 and CG, while the lowest diameter was recorded in the MT group (p < .05). Fish received TT showed normal dilated seminiferous tubule filled with large amount of free sperms within their lumen in a dose related effect. In conclusion, male Nile tilapia dietary supplementation with different inclusions of Tribulus terrestris extract specially 500 and 750 mg/kg diet improves growth performance, health condition, semen quality and reproductive efficiency without any harmful effect on water quality.     

Dualistic feeding pattern of Nile tilapia (Oreochromis niloticus,L.) reared under different self‐feeding system conditions

Nile tilapia (Oreochromis niloticus) is one of the most important cultured species worldwide. The research aims to clarify the feeding characteristics, such as daily feeding pattern of Nile tilapia using a self‐feeding technique. The feeding pattern was conducted under two rearing conditions, indoor treatments under a controlled light regime (LD 12:12) and constant water temperature (25°C), and outdoor treatments under natural conditions which consisted of duplicate trials with two periods each. The outdoor treatment was carried out from early summer through late autumn in Mie, Central Japan. Daily self‐feeding activity of Nile tilapia in indoor treatments was nearly daytime feeding pattern, synchronizing with the given photoperiod (24 hr). However, the self‐feeding activity in the outdoor experiments from early summer to early autumn was almost daytime feeding pattern, but it became less clear and shifted to a nighttime feeding profile in late autumn. The results revealed that Nile tilapia has a dualistic capacity for demand‐feeding both in light and dark phases. These results might have been caused by the seasonal change in light intensity and/or water temperature. Information obtained from the self‐feeding experiments enables us to identify the influence of environmental changes on the physiological condition of farmed fish through their expression of appetite.     

Plasmid‐mediated antimicrobial resistance in motile aeromonads from diseased Nile tilapia (Oreochromis niloticus)

For the sustainable farming of tilapia, proper maintenance of their health and adequate treatment for infections at appropriate time are inevitable. The indiscriminate use of antibiotics in aquaculture, as a part of treatment and as growth promoters, accelerates antimicrobial resistance (AMR) among the fish pathogens. In the present study, we have isolated diverse aeromonads from Nile tilapia and studied their antibiogram and plasmid profiling. Aeromonas hydrophila, Aeromonas veronii, Aeromonas sobria, Aeromonas dhakensis, Aeromonas caviae, Aeromonas jandaei and Aeromonas aquatica were isolated from infected tilapia (n = 150), and their Shannon wiener diversity index was calculated as 1.926. A. veronii was found to be the most multiple antibiotic‐resistant pathogen with the MAR index of 0.46, and A. aquatica was noticed as the least resistant isolate. The minimum inhibitory concentration of resistant antibiotics was shown as >256 mcg/ml for most of the isolates. The virulent genes such as aerolysin and hemolysin were identified in all the isolates except A. aquatica. The detection of class 1 integrons, plasmid profiling and plasmid curing studies confirmed that AMR exhibited by most of the Aeromonas species is of plasmid mediated. This challenges the risk of wide spread of AMR among the pathogens and subsequent treatment of the infection.     

Economic profitability of Nile tilapia (Oreochromis niloticus L.) production in Kenya

Economic profitability of Nile tilapia production in Kenya was analysed using a model that simulated individual fish growth and took fish population dynamics in the pond into account. The results suggest that the currently practiced mixed‐sex tilapia culture is economically unsustainable. It is suggested that research and extension efforts be geared towards developing monosex Nile tilapia production systems. Nile tilapia culture with African catfish predation should be viewed as an intermediate step towards all‐male Nile tilapia culture. This will allow accumulation of both physical and human capital to support all‐male tilapia culture. Under all‐male culture, economic returns are high enough to justify investment in Nile tilapia culture using borrowed capital. However, the success of monosex culture will depend on the availability and affordability of quality fingerlings and low‐cost fish feeds. The results have a wide application in Sub‐Saharan Africa where mixed‐sex Nile tilapia culture is common.     

Combined effects of dietary malic acid and Bacillus subtilis on growth,gut microbiota and blood parameters of Nile tilapia (Oreochromis niloticus)

The study investigated effect of dietary supplementation with malic acid, Bacillus subtilis and a mixture of the two (3 × 2 factorial trial) on Nile tilapia (Oreochromis niloticus) health. Treatment groups (T1–T6) were fed diets containing three levels of malic acid (0.0, 5.0 and 10.0 g/kg), each of which was supplemented with 0 and 1.1 × 10⁵ cfu/g B. subtilis, respectively. Each treatment group was assigned randomly to triplicate groups of 35 fish (5.26 ± 0.06 g) in 18 tanks for 84 days. The results indicated that survival was higher in all dietary treatments as compared to the control fed fish. The highest values of FBW, WG and SGR (%), PER, PPV and ER were recorded in groups T4 and T6, which were fed diets supplemented with 5 g malic acid/kg and 1.1 × 10⁵ cfu/g B. subtilis and 10 g malic acid/kg and 1.1 × 10⁵ cfu/g B. subtilis, respectively. The best value of FCR was obtained in groups T4 and T6. The lowest total bacterial count in the gut and faeces was detected in fish from group T6. The values of haematocrit, haemoglobin, red blood cells, white blood cells, total protein, albumin and globulin were significantly higher (p < .05) in fish from groups T4 and T6 (diets supplemented with malic acid and B. subtilis). As compared to the control fed fish, te mixture of these substances are promising as immune enhancher in aquacultured fish.     

Protein requirements of Nile tilapia (Oreochromis niloticus) fry cultured at different salinities

Effect of isolipidic (62.7 ± 5.0 g kg^?1) diets with protein levels of 204.6 (T20), 302.3 (T30), 424.6 (T40) or 511.0 g kg^?1 (T50) on growth and survival in Nile tilapia (Oreochromis niloticus Linnaeus 1758) fry cultured for 70 days at one of four salinities (0, 15, 20 and 25 g L^?1) was evaluated. A bifactorial (4 × 4) design was used with 16 treatments run in triplicate and 20 fry (0.25 ± 0.04 g) per replicate under semi‐controlled conditions. Four independent, recirculating systems (one per salinity level) were used, each one with 12 circular tanks (70 L capacity), filters and constant aeration. The different salinities had no significant effect on growth. Weight gain improved significantly as dietary protein content increased, although organisms fed the T50 diet had a lower growth rate. Survival was highest (98.33%) in the T50/15 (protein/salinity levels) treatment and lowest (71.0%) in the T20/20 treatment, with no pattern caused by the variables. The T40/25, T40/20 and T50/0 treatments produced the most efficient growth and feed utilization values while the T20 treatments at all the salinities resulted with the lowest performance. With the exception of the T50 treatments, a non‐significant tendency to increased weight gain was observed as water salinity increased, suggesting that the salinity of the culture environment does not influence dietary protein requirements in Nile tilapia O. niloticus fry.     

Effect of dietary probiotic Biogen® supplementation as a growth promoter on growth performance and feed utilization of Nile tilapia Oreochromis niloticus (L.)

Probiotic microbial feed supplements are gaining wide acceptance in livestock production, and may be applicable to aquaculture production systems. The present study was conducted to examine probiotic treatment in the fingerling diet of Nile tilapia Oreochromis niloticus (L.). A total of 240 of Nile tilapia fingerlings (weight ranged from 22.96 to 26.40 g) were divided into five experimental groups. The experiment was conducted for 120 days. Experimental diets were identical in all, except for the variation in probiotic levels. A probiotic (Biogen^®) was used at 0% (diet 1), 0.5% (diet 2), 1.5% (diet 3), 2.0% (diet 4) and 2.5% (diet 5) inclusion rates in the experimental diets. The growth performance and nutrient utilization of Nile tilapia including weight gain, specific growth rate, protein efficiency ratio, protein productive value and energy retention were significantly (P≤0.01) higher in the treatment receiving probiotic (Biogen^®) than the control diet. No differences were observed for moisture, ash and protein content (P≤0.01) among the experimental diets. The lowest gross energy and lipid contents were recorded for fish fed the diet containing 0.5% Biogen^® (P≤0.01). The production performance and subsequent cost–benefit analyses clearly indicated that the diets containing probiotic biogen recorded the highest net return and the lowest total cost compared with the control diet.     

Stable isotope analysis to quantify contributions of supplementary feed in Nile Tilapia Oreochromis niloticus (GIFT strain) aquaculture

Nile tilapia (Oreochromis niloticus) is currently one of the most farmed freshwater fish and contributes significantly to total global aquaculture production. The genetically improved strain of O. niloticus (GIFT) was introduced to Papua New Guinea (PNG) in 1999 to improve food and income security. The high cost and low availability of commercial fish feed hinder the growth of GIFT farming in PNG. Stable carbon and nitrogen isotopes were used to determine the role of supplementary and natural food sources in the diet of GIFT in pond‐based aquaculture. Two treatments were used: treatment 1 was daily feeding, and treatment 2 was weekly feeding, each with three replicates. Isotopic analysis of muscle tissue and all potential food sources showed that pellet feed contributed 7% to the growth of GIFT in daily‐fed ponds and 33% in the weekly‐fed ponds. Highly enriched δ¹⁵N values for chicken manure, compared to depleted values for GIFT and other natural food sources in both treatments, clearly indicate insignificant contributions of this input to production. After 90 days of cultivation, the average final body weight of GIFT receiving daily feed inputs was 134 g (average 19 cm), while for weekly‐fed it was 92 g (17 cm). The feed conversion ratio (FCR) was poor (6.4:1) in the daily‐fed GIFT ponds compared to a better, and preferable, FCR (1:1) in the weekly‐fed ponds. The findings of this study show that pelleted feed was not the major contributor to the growth of GIFT. Genetically improved farmed tilapia aquaculture should focus on enhancing natural food availability for fish production.     

Evaluation of fermented date palm seed meal with Aspergillus oryzae on the growth,digestion capacity and immune response of Nile tilapia (Oreochromis niloticus)

Five diets were prepared to include date palm seed meal (DSM) fermented with Aspergillus oryzae (ASP) at 0, 50, 100, 150 and 200 g/kg diet and fed for Nile tilapia (26.93 ± 0.01 g) for 8 weeks. Fermented DSM significantly affected the final weight, weight gain and specific growth rate in a dose‐dependent manner (p = .001) with insignificant differences in feed conversion ratio (p > .05). Dietary fermented DSM significantly increased the lipase, amylase and protease activities (p = .008, p = .001 and p = .01, respectively) and the Hb, RBCs and WBCs (p = .001, p = .005, and p = .009, respectively). The intestinal villus length and number of goblet cells were significantly affected by fermented DSM inclusion (p < .05). Additionally, the total protein, albumin and globulin significantly affected by the inclusion of fermented DSM in a dose‐dependent manner (p = .04, p = .045, and p = .03, respectively). Furthermore, dietary fermented DSM significantly altered the phagocytic index, phagocytic activity and lysozyme activity (p = .001, p = .045 and p = .04, respectively). Based on the polynomial regression analysis, the inclusion of fermented DSM at 103.3–164.8 g/kg diet can be used effectively in tilapia diets for improving the growth, digestion activity and immune response.