Polyculture of silver barb, Puntius gonionotus (Bleeker), Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L., in Vietnamese ricefields: feeding ecology and impact on rice and ricefield environment

Rice production, ricefield environment and the feeding ecology offish were studied in an experiment conducted at a rice-fish station in the Mekong Delta, Vietnam. In total, six treatments (three replicates) were investigated: four different polyculture combinations of small sized silver barb, Puntius gonionotus (Bleeker), Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinuso carpio L.; one treatment with pre-grown fingerlings; and a control treatment in which no fish were stocked. No insecticides or fungicides were utilized before or during the experiment. Frequent fertilization of the water and a low rice plant biomass during the early vegetative growth phase stimulated the development of phytoplankton and zooplankton. The total weed biomass was low (maximum = 5.3 g dry weight m^?2) and not significantly (P < 0.05) different between the treatments. A major component of the silver barb diet consisted of rice plants and accessible grains. However, the introduction of silver barb only had a significant effect on the number of rice tillers in the ratoon crop and not on the paddy yield. The quantitative differences in the diets of tilapia and common carp were minimal: both species fed mostly on detritus. Ricefields without silver barb produced the highest paddy yield (3120 kg ha^?1). The total yield of introduced fish increased after increasing the stocking density of silver barb from 319.9 to 494.1 kg ha-¹. The highest fish yield (541.8 kg ha-1) was obtained by stocking pre-grown fingerlings in the ricefields.     

Performance of common carp,Cyprinus carpio L. and Nile tilapia,Oreochromis niloticus (L.) in integrated rice–fish culture in Bangladesh

Irrigated rice fields have enormous potential for expanding the aquaculture production in rice producing countries. Two field experiments were carried out at the Bangladesh Agricultural University, Mymensingh, to optimize the productivity of integrated rice–fish systems using Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. Both experiments were laid out in a randomized complete block design with three replicates per treatment and regular rice monoculture as control. In the first trial, carp and tilapia were tested in single culture and in mixed culture with supplementary feeding at 2× maintenance level. The highest fish yield was obtained in the carp/tilapia mixed culture (586 ± 125 kg ha^− 1), followed by tilapia alone (540 ± 65 kg ha^− 1), and carp alone (257 ± 95 kg ha^− 1). Carp had significantly lower yield than the other two fish groups (p < 0.05) due to high mortality and inefficient feed utilization. As the carp/tilapia combination performed the best in the first experiment, it was tested with different inputs in the second trial, i.e. regular urea fertilization and two different feeding levels. The feeding levels were: continuous feeding at 2× maintenance level (feed level I) and a declining feeding schedule from 4× to 2× maintenance level (feed level II). The highest fish yield was obtained in feed level II (935 ± 29 kg ha^− 1), followed by feed level I (776 ± 22 kg ha^− 1), and the non-fed group (515 ± 85 kg ha^− 1). Yield differences between the treatments were significant at p < 0.05. Rice yields showed controversial effects between the rice–fish treatments and were dependent on the inputs provided. The highest rice production (4.2 t ha^− 1) was obtained from rice–fish plots with regular urea fertilization. Various significant effects of fish on water quality parameters were observed. Fish decreased the dissolved oxygen (DO) and pH value compared to rice only, especially when supplementary feed was provided. Moreover, fish stimulated the growth of phytoplankton and increased chlorophyll-a concentration. In conclusion, carp/tilapia mixed culture with supplementary feeding was found to be optimal for maximizing the output from rice–fish culture.     

Effect of three different oil cake-based diets on pond production performance of silver barb, Puntius gonionotus (Bleeker)

One of the three iso-nitrogenous (30% crude protein) and iso-energetic (15.0 MJ kg⁻¹ diet) oil cake-based diets (groundnut, D-1; soybean, D-2 and mustard, D-3) was fed to the fingerlings (6.61 ± 0.06 g) of silver barb ( Puntius gonionotus ) for 120 days in triplicate fertilized ponds (0.04 ha) with a stocking density of 9000 fish ha⁻¹. Fish were fed at 10% of their body weight for the first month, followed by 3% in the second and 2.5% in the third and fourth months of the culture period. The fish fed diets D-1, D-2 and D-3 grew from initial weights of 6.67, 6.67 and 6.50 g to 320.23, 298.23 and 305.13 g respectively. No significant variation ( P >0.05) was found in the growth and nutrient utilization of fish fed different dietary treatments. Net profits of Indian Rupees 67 385, 59 535 and 65 790 ha⁻¹ were obtained in fish fed D-1, D-2 and D-3, respectively, within 120 days of culture. The results of this study suggest the possibility of the use of mustard oil cake as a dietary protein source for pond culture of silver barb in addition to groundnut and soybean oil cakes without compromising the growth, nutrient utilization, production performance and economics of culture of this fish.     

Growth and fry production of Nile tilapia, Oreochromis niloticus (L.), on different feeding schedules

The effect of scheduled use of high‐protein and low‐protein diets on body weight and fry production of Nile tilapia, Oreochromis niloticus (L.), was determined. A preliminary feeding trial was first conducted on fingerlings. These were fed a high‐protein diet (H, 25% protein) or a low‐protein diet (L, 18% protein) daily, or diet H for 1–3 days followed by diet L for 1–4 days. Final body weight was significantly higher (P < 0.05) in fish fed diet H daily and in fish fed diet H for 2–3 days followed by diet L for 1 day (2H?1L and 3H?1L). Fingerlings on 1H?1L and 3H?2L had slightly lower growth. Based on the response of the fingerlings, five feeding schedules were tested with the broodstock. A high‐protein diet (HP, 40%) and a low‐protein diet (LP, 25%; same as H for fingerlings) were used. Feeding schedules significantly influenced body weight of female but not the male fish. Fry production was not significantly affected by the feeding schedule for broodstock. When growth, fry production and saving in feed cost were all considered, the broodstock on 1HP?1LP and 3HP?2LP feeding schedules both gave the highest overall performance. These findings give fish farmers an option in the management of feeding of tilapia broodstock.     

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.     

Total replacement of fish meal with animal protein sources in Nile tilapia,Oreochromis niloticus (L.), feeds

The effects of total replacement of dietary fish meal (FM) with animal protein sources on the growth, feed efficiency and profit indices of Nile tilapia, Oreochromis niloticus (L.), were investigated. Shrimp meal (SM), blood meal (BM), meat and bone meal (MBM), BM + MBM mix and poultry by-product meal (PBM) replaced FM in six isonitrogenous (30% crude protein), isocaloric (400 kcal GE 100 g^–1) diets. The diets were fed to O. niloticus fingerlings (12.5 g) to satiation twice a day for 150 days. The growth of fish fed SM, PBM and MBM was not significantly different from those fed the FM-based diet, while feed conversion and protein efficiency ratios were significantly retarded. Further reduction in fish performance was noticed when BM or BM + MBM replaced FM in the control diet. Cost–benefit analyses of the test diets indicated that these sources were economically superior to FM. The PBM-based diet produced higher carcass lipid than other diets. Fish fed SM, MBM and PBM diets had significantly higher ash contents (P < 0.05).     

Effect of Nile tilapia, Oreochromis niloticus (L.), size on phytoplankton filtration rate

Four different‐sized (390±3, 140±2, 40±2, 16±1 g) Nile tilapia, Oreochromis niloticus (L.), stocked at the same biomass in timed pulse feeding chambers were provided 27–29°C water dominated by Microcystis (82%) and Scenedesmus (18%) to determine the effect of fish size on filtration rates. The number of Microcystis and Scenedesmus units filtered from the water decreased significantly with increasing tilapia size. The shaping constants and maximum filtration rates for Ivlev's feeding model used to describe the relation between filtration rates and the suspended particulate organic carbon (POC) concentrations were significantly different among the four sizes. Filtration rates of 763, 671, 512 and 300 mg C kg^?1 h^?1, which correspond to 70%, 82%, 86% and 90% saturation levels, were achieved at POC levels of 30, 32, 32 and 33 mg C L^?1 for 16, 40, 140 and 390 g Nile tilapia respectively. Smaller tilapia achieved these rates at lower POC concentrations than larger tilapia.     

Replacing dietary corn with barley seeds in Nile tilapia, Oreochromis niloticus (L.), feed

Four isocaloric–isonitrogenous rations containing 0%, 15%, 30% and 51% of ground barley seeds as a replacement for dietary corn were fed to three replicate groups of Oreochromis niloticus (Linnaeus) fingerlings with a mean initial weight of 3.5 g. The randomly selected fish were tested for 9 weeks in 60 L circular tanks. Each tank was considered as an experimental unit. The tanks were put together in a water recirculating system using filtered and aerated ground well water (24 ± 3 °C). Tilapia weight gain, feed conversion, specific growth rate and protein efficiency ratio were similar in fish fed diets containing 15% and 30% barley and were superior to those fed diets containing 0% control and 51% barley. There were no differences between tilapia fed diets containing 0% and 51% barley. Body moisture, crude fat, crude protein and total ash did not change as the level of barley in the feeds was increased.     

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.     

Effects of sex ratio and feed quality on mass production of Nile tilapia, Oreochromis niloticus (L.), fry

Two experiments were conducted on Nile tilapia, Oreochromis niloticus (L.), in laboratory fibreglass tanks. The first experiment aimed to test the effects of four different sex ratios, which ranged from two to five females to one male, on mass production of fry. The lowest sex ratio (two females to one male) gave significantly the highest production, while the highest sex ratio (five females to one male) gave the lowest. The objective of the second experiment was to compare the effects of different diets which varied with regard to feed components (natural versus artificial). The diet composed of animal-plant protein (the standard artificial diet) in addition to natural food (65% phytoplankton and 35% zooplankton) gave significantly the highest fry production and the highest breeders’growth. Exclusively standard artificial diet gave significantly better fry production and better breeders’growth over the rest of tested diets except the above-mentioned one. The addition of natural food to the artificial diet enhanced fry production as well as the breeders’growth, and the better the quality of the artificial feed, the better the results obtained.     

Digestive capabilities of three commensal fish species: carp, Cyprinus carpio L., tilapia, Oreochromis aureus×O. niloticus, and African catfish, Clarias gariepinus (Burchell 1822)

Abstract. This paper examines the digestibility of different feed mixtures by three species of fish: carp, Cyprinus carpio L., tilapia, Oreochromis aureus × O. niloticus , and African catfish, Clarias gariepinus (Burchell 1822). Protein from poultry sources was digested better by tilapia than by carp or catfish, but no significant difference was found in the case of protein mainly from fish meal. Carp showed the best ability to digest fats, followed by catfish, with tilapia having the least ability. Tilapia digested carbohydrate better than the other two species, however, whether from wheat or corn sources. The same pattern applies to the digestibility of energy.     

A farmer-oriented Nile tilapia, Oreochromis niloticus L., breed improvement in the Philippines

Opportunities for developing small‐scale tilapia industry in the Philippines is hampered by the shortage of good‐quality seeds and broodstock. Most small‐scale farmers are dependent on distribution centres for improved tilapia seeds that are expensive and not sufficient to meet market demands. An option would be for farmers to develop their own tilapia breeds using simple procedures within their technical and financial resources. This option will also help sustain the diversity of locally adapted domestic stocks of tilapia. The Philippine tilapia production of ～122 316 MT can be increased by ensuring a stable supply of quality seeds and transferring suitable technology to fish farmers. The study was carried out in a tilapia hatchery/nursery pond in the Philippines to explore the potential for a farmer‐based research on tilapia breed improvement using relatively simple artificial selection procedures. One generation of size‐specific mass selection based on the early culling of large fry (collimation procedure) was applied on a Nile tilapia strain, Oreochromis niloticus L., in net cages set in a small earthen pond. Two episodes of directional selection were performed after initial removal of large fry at 21 days. Selection of parents and progeny testing were conducted in hapa and B‐net cages set in earthen ponds. The selection resulted in a significant response of 8% for standard length and 29% for weight relative to the control. The crude estimates of realized heritability is ～16% for standard length and ～26% for weight comparable with similar studies conducted by other workers.     

Ultraviolet-induced androgenesis in Nile tilapia, Oreochromis niloticus (L.), and hybrid Nile × blue tilapia, O. aureus (Steindachner)

Fertilization of ultraviolet (UV) irradiated oocytes of Nile tilapia, Oreochromis niloticus (L.), with sperm from O, niloticus or blue tilapia, O, aureus (Steindachner), and subsequent suppression of the first cleavage of fertilized eggs successfully induced androgenesis in Nile and blue tilapia. The optimal doses of UV irradiation to denucleate a female genome of Nile tilapia prior to androgenesis ranged from 5940 to 6930 erg mm^?2 for 54-63 s at a fixed intensity of 110 erg mm^?2 s^?1. Putative androgenetic fish were created from eggs which were irradiated at various times and several durations of heat-shock. Eggs which were treated for 5 min at 41.6 ^oC at 2 7.5 min after fertilization were the most successful at suppressing the first cleavage and producing viable androgenetic diploids in Nile or hybrid Nile X blue tilapia. The maximal survivals of putative androgenetic diploids in relation to the control were 1.60% and 0.90% in Nile and hybrid Nile X blue tilapia, respectively. The androgenetic offspring established exhibited active feeding and normal growth.     

Upper lethal and rearing temperatures for juvenile common carp, Cyprinus carpio L., and silver carp, Hypophthalmichthys molitrix (Valenciennes)

Abstract. The ultimate upper lethal temperature (UULT) was 43.0 or 46.0°C for common carp and 43.5 or 46.5°C for silver carp, depending on the method of calculation. The influence of fish age on lethal temperature values was low. Using the relationship between the UULT and the optimum growth temperature the latter was calculated as being 38°C for common carp and 39°C for silver carp. No significant differences were found in survival of fish reared at lower and higher temperatures when proper food was used.     

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.     

Francisella sp., an emerging pathogen of tilapia, Oreochromis niloticus (L.), in Costa Rica

Francisella sp. is an emergent bacterial pathogen that causes acute to chronic disease in warm and cold water cultured and wild fish species. During the past 3 years, the bacterium has been detected in tilapia, Oreochromis niloticus , cultured in Costa Rica. Infected fish presented non-specific clinical signs, such as erratic swimming, anorexia, anaemia, exophthalmia and high mortality. Upon macroscopic and microscopic examination, several internal organs (mainly spleen and kidney) were enlarged and contained white nodules. Histological examination revealed the presence of multifocal granulomatous lesions, with the presence of numerous small, pleomorphic, cocco-bacilli. The bacteria were isolated from infected tilapia on selective media and grown on several media with and without antibiotics. Specific PCR primers to the Francisella genus were used to confirm the preliminary diagnoses. In comparison with several bacterial 16S rRNA sequences, our isolate was found to share 99% identity with other Fransicella spp. isolated from fish, and more than 97% identity to the human pathogen Francisella tularensis . Koch's postulates were fulfilled after experimental intraperitoneal and gill exposure challenges.     

Storage of common carp, Cyprinus carpio L., eggs for short durations

In this study, a short-term storage of pre-activated eggs of the Japanese ornamental (koi) carp, Cyprinus carpio L., at three different temperature regimes is reported. Koi eggs were stored at low temperatures (6-9^oC), at variable or high temperatures (12-31C) and at moderate-stable temperatures (20-24.5^oC). Survival of the developing embryos was examined at the first and the second day post-activation, and in hatch-out larvae. Survival was calculated for each treatment by linear regression Y = a-bX (P± 0.01), except for eggs incubated at temperature of about 20 C(P > 0.1).The specific mortality index (b/a 100), as a ratio between the mortality rate (b) and the fertilization rate (a), indicated that the highest mortality is associated with the high and unstable storage temperatures, while the lowest mortality is with the moderate and stable storage temperatures. Eggs can be stored at moderate and stable temperatures for a maximal duration of 6h, yielding survival of hatch-out larvae higher than 50%. In two trials, fertilization potency of sperm stored in a domestic refrigerator (5-9^oC) for 5h, was compared with freshly stripped sperm and no differences in fertilization rates were found between the two treatments.