Approaches to national fish breeding programs: pointers from a tilapia pilot study

Details are given of a framework for developing breeding programmes using experience from the Genetic Improvement of Farmed Tilapias project which focussed on Nile tilapias (Oreochromis niloticus ). The following aspects are outlined: Analysis of targeted production and marketing systems; Breeding goals; Systematic documentation and evaluation of available genetic resources and choice and genetic base; Number of strains; Breeding strategy; Selection criteria and evaluation; Production and dissemination of improved strains; and, social, economic and environmental impacts.

Digestibility and nutrient utilisation of soybean bran-based diets in Nile tilapia Oreochromis niloticus

The digestibility and utilisation of two soybean bran-based diets and two fishmeal-based diets serving as control, at optimal (30%) and suboptimal (20%) protein levels were evaluated in Oreochromis niloticus. These were Diet I (Control)-fishmeal based diet at 30% crude protein, Diet II (Control) - fishmeal based diet at 20% crude protein, Diet III - hydrolysed Soybean Bran based diet at 30% crude protein, Diet IV - hydrolysed Soybean Bran based diet at 20%. Dry matter digestibility differed insignificantly with variation in diets (P<0.05). There was significant variation in the protein (p 20.05), lipid and ash digestibility. Protein was more digestible at optimum level than sub-optimum level, while lipid and ash digestibility did not vary with their inclusion levels. Variation in the utilisation of the diets was significant (P<0.05) except for survival. It was observed that the best diet was Diet 1, closely followed by Diet II with highest values of mean final weight, specific growth rate, protein efficiency ratio and the apparent net protein utilisation. The high digestibility values of Diets III and IV suggests their inclusion in fish diet to spare protein for growth

Toxicity of Gramoxone super(R) and detergent to nile tilapia (Oreochromis niloticus) L. fingerlings

Acute toxicity tests on the effects of Gramoxone and detergent (both applied as a single dose) to nile tilapia, Oreochromis niloticus, fingerlings (mean weight 2.7~c1 g) were conducted using static bioassay. The 96-h LC sub(50) of Gramoxone and detergent applied were 0.08ml/l and 0.004 g/l, respectively. The fingerlings showed increased hyperactivities exemplified by erratic movement, loss of reflex, and hyperventilation during the period of exposure. These effects increased with increasing concentrations of Gramoxone or detergent throughout the duration of exposure. Tilapia fingerlings of the same size showed different levels of tolerance to the same concentration of both pollutants

Selectivity of three aquatic weeds as diet for Nile tilapia (Oreochromis niloticus)

A total of sixty juvenile Oreochromis niloticus (Nile tilapia) were fed three species of aquatic weed, namely Azolla filiculoides (water fern), Elodea sp. and Pistia stratiotes (water lettuce) to determine which of the weeds will be selectively consumed, and preferred of all. A control group of twenty Nile tilapia was fed compounded feed. The selectivity of the weeds was observed based on their utilization as food source, and Azolla filiculoides was found to be highly utilized, followed by Elodea sp. and the roots of Pistia stratiotes. The growth response of the fish to the diets was found to be highest for fish fed compounded feed followed by Azolla filiculoides and Elodea sp., while Pistia stratiotes produced a negative growth trend. It is therefore postulated that Azolla filiculoides and Pista sp. are good feedstuffs for O. niloticus especially when used together with other feedstuffs

Effect of darting phenomenon of African catfish Heterobranchus longifilis (Burchell 1822) on growth performance of Nile tilapia: Oreochromis niloticus (Linnaeus, 1758)

Replicate Ponds of 0.02ha stocked at 500 catfishes with 20,000 tilapia/ha were used to assess growth performance of O.niloticus, average weight 50.4g with (i) darted catfish; H.longifilis (shooters) average weight 60.3g (ii) non-shooters of H.longifilis, average weight 35.4g. Final mean weight, mean growth rate, specific growth rate and food conversion ratio were 499.5g 26g/day, 1.36% and 5.58% respectively for O.niloticus stocked with longifilis (shooters and 440.4g 2.3g/day 1.23% and 5.58% respectively for O.niloticus stocked withH.longifilis (non- shooters) and 246.9g, 1.2g/day, 0.93, 6.30% respectively for tilapia in monoculture. The least growth was noted for O. niloticus in monoculture while the best growth was recorded O. niloticus in polyculture with darted catfish

Effect of darting phenomenon of African catfish Heterobranchus longifilis (Burchell 1822) on growth performance of Nile tilapia: Oreochromis niloticus (Linnaeus, 1758)

Replicate Ponds of 0.02ha stocked at 500 catfishes with 20,000 tilapia/ha were used to assess growth performance of O.niloticus, average weight 50.4g with (i) darted catfish; H.longifilis (shooters) average weight 60.3g (ii) non-shooters of H.longifilis, average weight 35.4g. Final mean weight, mean growth rate, specific growth rate and food conversion ratio were 499.5g 26g/day, 1.36% and 5.58% respectively for O.niloticus stocked with longifilis (shooters) and 440.4g 2.3g/day 1.23% and 5.58% respectively for O.niloticus stocked with H.longifilis (non- shooters) and 246.9g, 1.2g/day, 0.93, 6.30% respectively for tilapia in monoculture. The least growth was noted for O. niloticus in monoculture while the best growth was recorded O. niloticus in polyculture with darted catfish

Effects of substituting fish meal with grasshopper meal on growth and food utilization of the Nile Tilapia, Oreochromis niloticus fingerlings

The effects of substituting fish meal with grasshopper meal in fish diets on the growth, food utilization and survival of the Nile tilapia, Oreochromis niloticus (mean weight = 40.1g) were investigated. The results show that the best growth and food utilization were recorded in the fingerlings fed in the 10% grasshopper meal and 30% fish meal while the poorest growth and food utilization indexes were recorded with the 25% grasshopper meal and 15% fish meal. In general, at 10% inclusion, the fingerlings performed even better than the control (40% fishmeal and no grasshopper meal)

Rents drain in fishery: the case of Lake Victoria Nile Perch fishery

Many fisheries are potentially very valuable. According to a recent report by the World Bank and the FAO (2008), global fisheries rents could be as high as US$ 40-60 billion annually on a sustainable basis. However, according to the report, due to the “common property problem”, most fisheries of the world are severely overexploited and generate no economic rents. The Lake Victoria Nile perch fishery could be among the most valuable fisheries in the world. Unfortunately, also this fishery has fallen prey to the common property problem with excessive fishing effort, dwindling stocks and declining profitability. As a result, there is a large and growing rents loss in this fishery (compared to the optimal) reducing economic welfare and economic growth opportunities in the countries sharing this fishery. As in other fisheries, the biological and economic recovery of this fishery can only come though improved fisheries management

Managing Nile perch using slot size: is it possible?

The fishery of Lake Victoria became a major commercial fishery with the introduction of Nile perch in 1950s and 1960s. Biological and population characteristics point to a fishery under intense fishing pressure attributed to increased capacity and use of illegal fishing gears. Studies conducted between 1998 to 2000 suggested capture of fish between slot size of 50 to 85 cm TL to sustain the fishery. Samples from Kenya and Uganda factories in 2008 showed that 50% and 71% of individuals processed were below the slot size respectively. This study revealed that fish below and above the slot has continued being caught and processed. This confirms that the slot size is hardly adhered to by both the fishers and the processors. The paper explores why the slot size has not been a successful tool in management of Nile perch and suggests strategies to sustain the fishery

Selectivity of gillnets for Nile perch, Lates niloticus (L.), in Lake Victoria, Kenya

Four fleets of hanging coefficients 0.2, 0.4, 0.6 and 0.8 were used to determine size selectivity and selection factors of Nile perch populations. There was a linear relationship between mesh size and modal length of capture. Positively skewed length frequency distributions were found for smaller mesh sizes with entanglement becoming more prominent in mesh sizes above 101 mm. Nets of 114 to 141 mm stretched mesh yielded higher economic returns than small meshes, the catch consisting of few largefish.

Catch trends from Lake Victoria - Tanzanian waters

Catch trends from Fisheries Department reports from the last eleven years (1985-1995) were analyzed. These showed a shift in the fishery from a cichlid-based system to one dominated by Nile perch and tilapias. In recent years, catches have declined from a peak in the early 1990s. Catch per unit effort appears to have remained stable except for a drop in 1995, however, this is considered dubious because the effort showed a doubling in that year. Limitations of the fisheries data collection system for the Tanzanian sector of Lake Victoria are highlighted and discussed.

Changes in feeding biology of Nile tilapia, Oreochromis niloticus (L.), after invasion of water hyacinth, Eichhornia crassipes (Mart.) Solms, in Lake Victoria, Kenya

Oreochrimis niloticus (L.) was introduced to Lake victoria in the 1950s. It remained relatively uncommon in catches until 1965, when the numbers began to increase dramatically. It is now the third most important commercial fish species after the Nile perch, Lates niloticus (L.) and Rastrineobola argentea (Pellegrin). Oreochromis niloticus is considered a herbivore, feeding mostly on algae and plant material. The diet now appears to be more diversified , with insects, fish, algae and plant materials all being important food items. Fish smaller than 5 cm TL have a diverse diet but there is a decline in the importance of zooplankton, the preferred food item of small fish, as fish get larger. The shift in diet could be due to changes which have occurred in the lake. Water hyacinth, Eichhornia crassipes (Mart.) Solms, which harbours numerous insects in its root balls, now has extensively coverage over the lake. The native fish species which preyed on these insects (e.g. haplochromines) have largely been eliminated and O. niloticus could be filling niches previously occupied by these cichlids and non cichlid fishes. The change in diet could also be related to food availability and abundance where the fish is feeding on the most readily available food items.

Doses efficaces en glyphosate et en 2,4-D pour le contrôle chimique des laitue d'eau (Pistia stratiotes, Linn.) et toxicité du glyphosate vis-à-vis des tilapias (Sarotherodon melanotheron)

The toxic effects of two herbicides Round up (gliphosate) and 2,4-D (herbazol) were tested on Pistia stratiotes (Linn. Araceae) samples cultivated in glass aquariums. The gliphosate appears to be more toxic on Pistia Stratiotes than 2,4-D. It was then tested on tilapia Sarotherodon melanotheron juveniles. The lethal dose for tilapia (CL50 = 13.25 mg.l -1) is about 18, 37 and 74 times higher than the glyphosate toxic dose for plants at 1, 2 and 4 meters water depth respectively.

Pawpaw seed as fertility control agent on male Nile tilapia

To find out if pawpaw (Carica papaya) seeds can induce sterility in male Nile tilapia (Oreochromis niloticus) and to determine if sterility so induced is reversible or otherwise, mature male tilapia of mean weight 40 g were treated for 30 days with a low dose (4.9 g/kg/day) and a high dose (9.8 g/kg/day) of ground pawpaw seeds incorporated into their feed. Fish of similar sizes in the control experiment were fed with feed that did not contain pawpaw seed. The pawpaw seeds induced permanent sterility in the fish that received the high dose, while sterility in the low dose treatment was reversible. Fish in the control experiment spawned two weeks into the experiment and again in the fifth week. Fish in the low dose treatment spawned three weeks after the treatment had been discontinued. Histological sections of the testes showed that pawpaw seeds produced swollen nuclei in the low dose treatment and disintegrated cells in the high dose treatment. The study showed that pawpaw seeds, which are easy to obtain, can be incorporated into fish feeds and used by farmers to control prolific breeding of Nile tilapia.

Biochemical and morphometric approaches to characterize farmed tilapias

Biochemical (electrophoresis and mitochondrial DNA) and morphological analysis are important tools for the characterization of strains. Reference is made to studies conducted in the framework of the Genetic Improvement of Farmed Tilapias project to establish a new base tilapia population for culture purposes, describing the basic concepts of electrophoresis and morphometric analysis.