Small-scale fry production systems for Nile tilapia, Oreochromis niloticus (L.)

Abstract Experiments were conducted to evaluate and compare the production, quality and survival of eggs and the subsequent growth and survival of fry in two small-scale production systems: natural incubation and egg collection followed by artificial incubation. Artificial incubation produced a significantly greater number and biomass of fry per unit weight of female broodstock (P < 0·05). This was due to the significantly decreased spawning interval in females from which eggs were collected (mean = 23· days) compared to naturally incubating females (mean = 36·8 days). It is also hypothesized that survival during artificial incubation (85%) is greater than in natural incubation. Cost-benefit analysis demonstrated a threefold increase in total net returns for artificial incubation.     

Improving spawning synchrony in the Nile tilapia, Oreochromis niloticus (L.)

Abstract. The development stage and number of seed (eggs and fry) removed from individual incubating Oreochromis niloticus (L.) broodfish at 10-day interharvest intervals (IHI) was compared with the harvest of free-swimming fry from undisturbed fish held in a tank within the same system. Spawning synchrony and productivity were compared for (1) total exchange of females for ‘conditioned’ females after each harvest, (2) exchange of only spawned females, and (3) return of females back into the spawning tank. Improved synchrony and seed production were positively related to removal of eggs and fry from incubating females and could have important implications for broodstock management in commercial hatcheries. Allowing fish to remain undisturbed in clear water tanks may lead to inhibition of spawning activity related to the formation of hierarchies. Individual weight loss by females during incubation was correlated with stage of seed harvested and thus with timing of spawning during the interharvest interval.     

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

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

Effect of fluoxymesterone on sex ratio and growth of Nile tilapia, Oreochromis niloticus (L.)

The androgenic and anabolic potential of fluoxymesterone (FM) was evaluated by incorporating the hormone into the feed of Nile tilapia, Oreochromis niloticus(L.) fry. Phenotypic all-male populations were produced when FM was given at 1, 5 and 25mg/kg of feed. Fry fed methyltestosterone (MT) at 60 mg/kg of feed and 0-2 mg of FM per kg of feed had a sex ratio of 97-7% and 87-3% phenotypic males. No positive anabolic effect was evident in response to adding FM or MT to the feed at the end of the 28-day treatment period or after an additional 6 weeks of growth without hormone. Growth was less for fry which received 25 mg/kg of FM compared to those receiving lesser rates of FM, 60 mg/kg MT, and controls.     

Cyclical feed deprivation and refeeding fails to enhance compensatory growth in Nile tilapia, Oreochromis niloticus L.

A 12-week experiment was carried out to evaluate compensatory growth of 6.6 g Nile tilapia Oreochromis niloticus L. under three cyclical regimes of feed deprivation and refeeding. The deprivation and refeeding regimes included four cycles of 1 week of deprivation and 2 weeks of refeeding (S1F2), two cycles of 2 weeks of deprivation and 4 weeks of refeeding (S2F4) and one cycle of 4 weeks of deprivation and 8 weeks of refeeding (S4F8). A group of fish fed to satiation twice daily throughout the experiment served as control. At the end of the refeeding periods, fish deprived and refed cyclically had higher feed intake and specific growth rates (SGR), but lower body weight, than that of the control fish. There was no significant difference in feed efficiency ratio (FER) between the control and fish subjected to feed deprivation during the refeeding periods, and nitrogen retention efficiency (NRE) was not different between any two treatments throughout the experiment. At the end of the experiment, fish subjected to feed deprivation had lower body weight but similar body composition, relative to those of the control fish. No significant differences were found in final body weight, NRE and body composition between the fish subjected to different cycles of deprivation and refeeding, but the fish subjected to one cycle of deprivation and refeeding exhibited high mortality. Our results indicate that partial growth compensation induced by various cycles of feed deprivation and refeeding does not confer a huge advantage in terms of enhancing the production efficiency and reducing the nitrogen waste output in Nile tilapia farming 29–30 °C.     

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.     

MyoD,myogenin and proliferating cell nuclear antigen expression in growing Nile tilapia (Oreochromis niloticus L.)

In the present study, immunohistochemical and morphometric analysis was used to characterize variations in muscle growth performance during muscle fibre recruitment and hypertrophy. As in fisheries, fish were classified into four age stages: alevin 35 days (0.65±0.08 g); juvenile 60 days (13.67±1.35 g); adult 90 days (73.18±4.70 g) and adult 190 days (349.76±34.62 g). The number of nuclei expressing MyoD and myogenin was similar in alevin, juvenile and adult 90 days; however, in adult 190 days, the number of nuclei expressing myogenin was higher than the number expressing MyoD. The number of proliferating cell nuclear antigen‐stained nuclei in each stage was higher than MyoD and myogenin staining with peaks in alevin and adult 90 days. These data suggest that growth per se stimulated cellular proliferation and nuclei accretion of Nile tilapia muscle fibres in alevin, juvenile and adult 90 days. Muscle fibre differentiation was more pronounced in adult 190 days.     

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.     

Genotyping of Streptococcus dysgalactiae strains isolated from Nile tilapia,Oreochromis niloticus (L.)

Streptococcus dysgalactiae is an emerging fish pathogen that is responsible for outbreaks of disease on fish farms around the world. Recently, this bacterium was associated with an outbreak at a Nile tilapia, Oreochromis niloticus (L.), farm in Brazil. The aim of this study was to evaluate the genetic diversity, best genotyping method and aspects of molecular epidemiology of S. dysgalactiae infections in Nile tilapia farms in Brazil. Twenty‐one isolates from four farms located in different Brazilian states were characterized genetically using pulsed‐field gel electrophoresis (PFGE), ERIC‐PCR, REP‐PCR and sodA gene sequencing. The discriminatory power of the different typing methods was compared using Simpson's index of diversity. Identical sodA gene sequences were obtained from all isolates, and ERIC‐PCR and REP‐PCR were unable to discriminate among the isolates. PFGE typing detected three different genetic patterns between the 21 strains evaluated; thus, it was the best genotyping method for use with this pathogen. The strains from Ceará State were genetically divergent from those from Alagoas State. The S. dysgalactiae isolates analysed in this study constituted a genetically diverse population with a clear association between geographical origin and genotype.     

Characterization and comparison of variations in reproductive performance of Chitralada strain Nile tilapia, Oreochromis niloticus (L.)

In an attempt to better understand and characterize the variability in the female reproduction of individual Thai‐Chitralada strains of Nile tilapia, Oreochromis niloticus (L.), tagged mature females (n=68) from a single population were monitored in a hapa‐in‐pond system over a 12‐month experimental period. Spawn female⁻¹, eggs female⁻¹ day⁻¹, eggs kg female⁻¹ day⁻¹, day spawn⁻¹ and weight (g) at first spawning of individual females were determined from the regular weekly sampling of weight (g) and eggs per spawn. For analysis, the females were grouped into two, high spawning (HSF) and low spawning frequency (LSF) classes based on their spawning frequency (SF) record. Moreover, nested under these two classes were two groups each based on growth rate, i.e., high frequency – large size (HL), high frequency – small size (HS), low frequency – large size (LL) and low frequency – small size (LS). There was no difference in eggs spawn⁻¹ among all females. The HSF group produced 68% and 361% more eggs female⁻¹ day⁻¹ than the population mean and LSF group respectively. Eggs female⁻¹ day⁻¹ and spawn female⁻¹ remained high in the HSF group and low in the LSF group throughout the 12‐month experimental period. This suggests that individual female spawning activity is consistent within a population in a common environment. The inter‐spawn interval increased with age in all four groups, and day spawn⁻¹ was shorter by 130% in HSF females compared with day spawn⁻¹ in LSF. The HSF group also spawned more successively (≥3), while the LSF group of females had fewer successive spawns (≤2). Body weight (g) had no influence on the number of eggs produced. The study indicates that separating frequently spawning females could be used as an important strategy to improve commercial seed production of Nile tilapia.     

Effects of stocking density and feeding levels on growth and feed efficiency of Nile tilapia (Oreochromis niloticus L.) fry

The effects of stocking density and feeding levels on larval survival, growth rates, feed utilization efficiency and body composition of Nile tilapia (Oreochromis niloticus L.) fry were investigated in two consecutive experiments. In experiment 1, swimup fry (0.016 g average body weight) were stocked in 20‐L fibreglass tanks, in a closed, recirculating indoor system, at five stocking densities (3, 5, 10, 15 and 20 fry L^?1) and fed a larval test diet (40% crude protein) to apparent satiation, three times a day, for 40 days. Fish survival, percentage weight gain and specific growth rate (% SGR) were negatively correlated with stocking density. The best performance was achieved at 3 fry L^?1. However, no significant differences in growth parameters were found between 3 and 5 fry L^?1. Body composition was not significantly affected by stocking density. In experiment 2, fry (0.016 g average body weight) were stocked at 5 fry L^?1, and fed a larval test diet (40% crude protein) at six feeding levels (10%, 20%, 25%, 30% and 35% BW day^?1) and to satiation, three times a day for 40 days. Fish growth rates and survival were extremely poor at 10% feeding level, and improved significantly with increasing feeding levels up to 30%, and levelled off with further increase in feeding levels. On the contrary, feed conversion ratio (FCR) and protein production value (PPV) were negatively correlated with feeding level. The lowest feeding level (10%) produced significantly lower body lipid and higher protein and ash than other feeding levels. The present results suggest that the optimum stocking density and feeding level of Nile tilapia fry are 5 fry L^?1 and 30% per day respectively.     

Use of shrimp protein hydrolysate in Nile tilapia (Oreochromis niloticus, L.) feeds

A 45-day feeding trial was carried out to evaluate the use of shrimp protein hydrolysate (SPH) in diets for Oreochromis niloticus, L. SPH was included in isonitrogenous diets replacing fish meal protein by 0, 5, 10, and 20% and offered to Nile tilapia juveniles (1.7 ± 0.4 g) stocked in 40-L glass aquaria. The inclusion of SPH produced no significant differences (P ≥ 0.05) in final weight, survival, weight gain, average daily gain, specific growth rate, feed conversion ratio, protein efficiency ratio, or apparent net protein utilization. The inclusion of SPH Nile tilapia diets significantly affected (P < 0.05) the final fish body composition. Protein and ash contents decreased and fat content increased slightly with the increase in SPH. This study has demonstrated that SPH is a promising protein feedstuff and could account for as much as 6% of Nile tilapia diets with no adverse effects on growth and nutrient utilization.     

Control of reproduction in Nile tilapia Oreochromis niloticus (L.) by photoperiod manipulation

A major problem in tilapia aquaculture is the frequent reproduction of female fish, leading to increased competition for supplemented food and stunted somatic growth. The feasibility of using photoperiod manipulation to arrest the reproductive performance of tilapia Oreochromis niloticus was therefore examined. Newly hatched O. niloticus were reared in the laboratory under 12L:12D photoperiod at 28 °C. Fish (230–340 g) were maintained under 6L:6D, 12L:12D and 14L:10D photoperiod at 28 °C during the course of this study. Effect of photoperiod manipulation on reproductive parameters of fecundity, gamete quality, offspring viability and overall reproductive success were evaluated. Steroid levels (estradiol-17β, E₂; testosterone, T) during the spawning cycles of fish were analyzed on days 1 and 3 postspawning and at 3-day intervals thereafter. A total of 72 female fish from each photoperiod treatment were investigated the changing pattern of E₂, T and GSI with fish that have spawned once, twice and three times. Fish exposed to 12L:12D and 14L:10D photoperiod spawned successfully throughout the study. Whereas the spawning of fish exposed to 6L:6D photoperiod was arrested after three to four spawning cycles. The arrestment of spawning in fish exposed to 6L:6D photoperiod was paralleled by a significant decrease in plasma levels of E₂ (P<0.05). By contrast, there was no major difference in T levels among the treatments. These findings suggest that photoperiod manipulation can be used to arrest the spawning in tilapia O. niloticus. The utility of this in controlling the problem of overcrowding due to excess offspring in tilapia aquaculture is applicable.     

Simulation of the effects of oxygen on food consumption and growth of Nile tilapia, Oreochromis niloticus (L.)

Fish need oxygen for aerobic generation of energy for body maintenance, locomotion, feeding and biosynthesis. The rate of oxygen uptake of most fish is limited by diffusion through the gills, and gill surface area grows at a slower rate than body mass. We hypothesize, therefore: (1) that the maximum rate of feed intake is related to the capacity to take in oxygen for processing of this feed; and (2) that the maximum rate of feed intake relative to body size decreases with increasing body size to a point where growth is zero. An oxygen limitation module based on this theory was incorporated into an existing dynamic simulation model for the Nile tilapia, Oreochromis niloticus (L.). The module calculates the maximum potential oxygen supply to the fish on the basis of Fick's law of diffusion and the allometric relationship between body weight and gill surface area. Total oxygen demand of the fish is computed as the sum of routine metabolism, feeding metabolism and energy needed for biosynthesis. In the module, the feeding rate is limited to a level where total oxygen demand does not exceed the potential supply. The model is used to simulate feeding and growth of O. niloticus. Simulation results provide strong support for the oxygen limitation theory. Hence, the model can be used for the analysis of fish growth as affected by feed amount, feed composition, as well as environmental conditions (temperature, dissolved oxygen concentration). It also explains differences in final size between fish species, and within species under different conditions.     

Effect of feeding different grain sources on the growth performance and body composition of tilapia, Oreochromis niloticus (L.)

Growth performance and body composition of tilapia Oreochromis niloticus (L.), fed isonitrogenous and isoenergetic diets containing different grain sources (maize, wheat, barley, sorghum and rice) at a level of 25% were studied for a period of 62 days. Fish fed a diet containing sorghum showed the maximum weight grain, highest specific growth rate (SGR, 2.23), the best feed conversion (FCR, 1.07) and protein efficiency ratio (PER, 2.42) in comparison with all other diets. The diets containing maize, wheat and rice did not show any significant (P < 0.05) differences between each other. The barley diet showed the poorest values (SGR, 2.05; FCR. 1.34; PER, 1.98: and NPR, 30.65) in comparison with others. Although the diet containing sorghum showed the best net protein retention (NPR, 36.21) values, the results did not differ (P > 0.05) among maize, wheat and sorghum diets. The sorghum diet produced fish with lower moisture but higher body fat contents as compared to others. The fish fed diets containing maize, wheat, barley and rice did not show any significant difference (P > 0.05) in their body moisture and fat contents. The source of grain in the diet did not affect the crude protein and ash contents of fish (P > 0.05). It is suggested that cereal grains at the 25% level can efficiently be utilized in tilapia diets, sorghum being the best.     

Evaluation of the link between gyrodactylosis and streptococcosis of Nile tilapia, Oreochromis niloticus (L.)

Streptococcus iniae and Gyrodactylus niloticus are two common pathogens of cultured Nile tilapia, Oreochromis niloticus. We studied concurrent infection of tilapia by G. niloticus and S. iniae and evaluated whether parasitism in tilapia with Gyrodactylus increased susceptibility and mortality following immersion infection with S. iniae. Results showed that death mainly occurred in fish with G. niloticus and challenged with S. iniae (G-S group). The accumulative mortality (42.2%) was significantly higher in the G-S group than in fish not infected by the parasite (6.7%), but exposed to S. iniae. Bacteriological examination revealed S. iniae from > or =92% of dead or moribund fish challenged with S. iniae. Gyrodactylus not only damaged fish epithelium and provided entry for invasive bacteria but also was found to harbour viable cells of S. iniae for 24 and 72 h. Streptococcus iniae was isolated from 60% and 40% of G. niloticus collected from fish infected by intraperitoneal injection or immersion, respectively, at 24 h post-challenge. The present study confirms that parasitism of tilapia by G. niloticus increased host mortality following exposure to the bacterial pathogen S. iniae.     

Overwintering performance of Nile tilapia Oreochromis niloticus (L.) broodfish and seed at ambient temperatures in northern Vietnam

Two experiments (E1 and E2) to assess the performance of tilapia broodstock and tilapia sex‐reversed fry in overwintering were conducted at the Research Institute for Aquaculture No.1 (RIA‐1) in the cold seasons of 1995–96 and 1996–97. Nile tilapia Oreochromis niloticus (L.) broodstock of the Thai, GIFT, Egypt and Viet strains were overwintered in deep and shallow ponds, as well as in deep and shallow hapas suspended in a single deep pond for evaluation of the influence of overwintering systems on the survival and growth of fish. Large (> 1 g) and small (< 1 g) tilapia seed were overwintered in deep hapas‐in‐ponds for comparison of their performance. In 1995–96, the coldest pond water temperature was 10–11 °C, and survival of tilapia broodfish overwintered in deep and shallow hapas‐in‐ponds was 99.6–100%. This was significantly (P < 0.05) higher than fish stocked in deep and shallow ponds (74.4–90%). The survival rate of larger monosex tilapia fry was 54%, which was significantly (P < 0.05) higher than that of smaller fry (33.4%). In 1996–97, the lowest pond water temperature was 15.8 °C, and fry showed similarly high survival rates in all treatments (97–100%). There was no significant difference between fry in the two size classes. The results of this study clearly indicate that hapas‐in‐ponds are useful for reducing the risk and improving the survival of tilapia broodstock and fry in the cold season. Differences in the decline in ambient temperatures year on year mean that the need for special overwintering conditions varies. Hapas‐in‐ponds are a low‐cost overwintering method that can be one of the appropriate strategies for tilapia seed production under the variable, cool temperature regimes in northern Vietnam.