Search

Rapidly increasing hatchery-raised Nile tilapia (Oreochromis niloticus) in most developing countries lack informed recommended fingerling weight for stocking in semi-intensive grow-out ponds. The current study assessed the growth performance, survival and productivity of all-male Nile tilapia fingerlings of 0.2 g, 1 g, and 5 g in an on‐farm experiment. The final mean weight of fingerlings stocked at size 5 g was significantly higher (113.80±4.21 g) (P

Aquaculture must grow above the current rate of 11% per year to meet projected demand and reduce dependence on seafood imports. Government support and private investment are urgently needed for sustainable growth.

This paper discussed the conservation efforts of fish farmers of two endangered fish species in Lake Victoria namely Oreochromis variabilis and O. esculentus. Highlights focused on the determination of their growth performance under culture conditions, assessing their suitability for aquaculture, recruiting farmers to culture the species and testing the suitability of new dams and ponds for aquaculture. Both species breed easily under culture conditions. Therefore production of the fingerlings and their subsequent stocking in ponds, small water bodies and other larger water masses, including Lake Victoria, was a course of action implemented by the fish farmers to bring about their restoration.

WorldFish initiated a selective breeding program in Abbassa—Egypt to develop and produce the genetically improved Nile tilapia strain known as “Genetically Improved Abbassa Nile tilapia (GIANT)”, adopting the same technology used for the Genetically Improved Farmed Tilapia (GIFT), in Asia. WorldFish provided the Ninth Generation (G9) broodstock of the GIANT to 11 Broodstock Multiplication Centers (BMC’s) in five governorates; these centres then disseminated improved mixed‐sex fry to 160 tilapia hatcheries which supplied all‐male fry to 1,500 fish farms in 2017. We present results of an impact assessment of the G9 of GIANT in 83 of these fish farms in four Egyptian governorates (Kafr El‐Sheikh, Fayoum, Behera and Alexandria). Results indicate that the use of GIANT in all governorates achieved significantly higher (18.8%) fish yields (12.3%–26.4%) and 15.7% lower FCR (feed conversion ratio), reflecting a positive impact on their net profits compared with those who used commercial strains. Overall, fish farmers who stocked GIANT had significantly higher average fish sales (5,567 US$/ha) than those who stocked non‐improved commercial strains (5,192 US$/ha) in all governorates. However, when comparing within governorates, the difference was significant only in Fayoum and Alexandria noting a mixed performance of the GIANT strain. The mixed performance indicates that some hatcheries may have crossed the different strains, which lowered the performance differences. To get an objective analysis of the performance of the GIANT, it is recommended that similar assessment be undertaken with new generations of the strain supported by on‐farm performance trials.

Although, High Dam Lake small-scale fisheries is an important source of fish for residents of Aswan in Upper Egypt, there is limited information available about the performance of small-scale fisheries value chain. Structured questionnaires with fishers, traders, and processors were used to collect input and output data at each node of the chain. Focus group discussions meeting with stakeholder collected qualitative information about and critical factors influencing performance across the chain. Catch distribution composed mainly from tilapias 75%. While pebbly fish (Alestes spp.) and tigerfish (Hydrocynus spp.) accounts for 13% of catch. Fish processing is an important subsector in lake fisheries. Fishers obtained a relatively low percentage (49%) of the final consumer price. The recorded average catch per fisher 20 kg/day and the average total fishing cost in the three landing sites was EGP 5210 / t. Every 100 metric tons of fish catch and sell provides around 30 full-time equivalent jobs. This study revealed that fish stock is under pressure of overfishing. Critical factors facing the small-scale fisheries and influencing profitability are numerous. This value chain study improves our understanding of the performance of small-scale fisheries and identified limiting factors and action needed to support fisheries development in the lake. Key words: Small-scale fisheries, value chain, tilapia, tigerfish, pebbly fish.

This study evaluated the effect of dietary aflatoxin B1 (AFB1) on growth, milt and egg quality in matured Nile tilapia (Oreochromis niloticus). Triplicate groups of Nile tilapia (initial body weight 24.1 ± 2.6 g) were fed with either of four diets (Diets 1 to 4) designed to contain 0, 20, 200 and 2000 μg AFB1 kg-1 diets for 24 weeks. After 24 weeks of AFB1 exposure, growth was significantly (P

Poor culture conditions in low input ponds make fish highly susceptible to infectious pathogens which lead to diseases and mortalities yet the effects of probiotics on immunity, gut microbiota and microbiological quality of fish in low input ponds are unknown. Nile tilapia, Oreochromis niloticus fingerlings (40 g) were randomly stocked at 50 fish m-3 in 1.25 m3 cages in low input ponds. The fish were fed on diets supplemented with either Saccharomyces cerevisiae (1 × 1010 CFU g-1) or Bacillus subtilis (1 × 109 CFU g-1) at six levels: Diet 0 (No probiotic); S. cerevisiae at 2 g kg-1 (Diet 1); 4 g kg-1 (Diet 2) and 6 g kg-1 (Diet 3) and B. subtilis at 5 g kg-1 (Diet 4); 10 g kg-1 (Diet 5) and 15 g kg-1 (Diet 6) for 180 days. Results indicate that hemato-immunological parameters (hemoglobin (Hb), red blood cells (RBC), white blood cells (WBC) serum protein, albumin, globulin and lysozyme activity) were significantly higher in fish fed on probiotic treated diets compared to the control (P 0.05). Additionally, fish fed on probiotic treated diets retained the probiotics in their guts and lower microbial load was realized in their muscle (P < 0.05). In conclusion, B. subtilis and S. cerevisiae supplementation in diets of Nile tilapia reared in low input ponds improves immunity, manipulates gut microbiota and enhances fish flesh quality.

Warm water aquaculture is widely practiced in Kenya and is dominated by the culture of Nile tilapia (Oreochromis niloticus) (75% of total production) followed by African catfish (Clarias gariepinus) at 18%. Aquaculture started in Kenya in 1920’s and has been on upward trend until 2014 when it peaked at 24,096 MT. However, production reduced drastically in the past 3 years, with 14,952 metric tonnes (MT) reported in 2016. Most farmers practice earthen pond based semi-intensive culture system. Commercial intensive culture of Nile tilapia (O. niloticus) in cages in Lake Victoria has grown significantly in the last five years with a production of 12 million kg of fish every cycle (about 8 months). Recirculation aquaculture system (RAS) is also gaining popularity mainly in intensive hatcheries. The freshwater cages have been marred by increasing frequencies of fish kills with obvious financial and environmental implications. Although limited information exists on fish disease outbreaks across the country, certain well known diseases in farmed fish have been reported. These include; fungal, mainly saprolegniasis, bacterial, mainly hemorrhagic disease and pop-eye diseases. Parasites have also been documented in farmed O. niloticus and C. gariepinus. Although prophylactic treatments are used in some hatcheries in order to prevent infections, limited biosecurity measures are in place to prevent diseases in farmed fish. This is because of inadequate knowledge of the economics of fish diseases, poor infrastructure and inadequate human resource specialized in fish diseases. This review describes the aquaculture production and health mangement practices of farmed fish in Kenya in order to document actions required for effective monitoring and regulation of future fish health problems across the country. Keywords: Aquaculture, Culture systems, Fish health, Hemorrhagic disease, Nile tilapia, Saprolegniasis

A total of 52 samples of finished fish feeds and ingredients were collected from smallholder farmers in Kenya, Tanzania, Rwanda and Uganda, and analyzed. Culture and molecular techniques were used to identify fungal isolates from the feedstock, and mycotoxin profiles were determined using liquid chromatography–tandem mass spectrometry. The most prevalent fungal species recovered in the samples was Asperigillus flavus (54.5%). Other fungal species recovered from the samples were Aspergillus tamarii (9.1%), Mucor velutinosus (9%), Phoma sp. (6.1%), Aspergillus niger (6%), Eurotium rubrum (3%) and Penicillium chrysogenum (3%). Fourteen mycotoxins were identified: aflatoxins B 1 , B 2 , G 1 and G 2 , fumonisin B 1 and B 3 , deoxynivalenol (DON) and acetyldeoxynivalenol (sum of 3-ADONand 15-ADON), ochratoxin A, roquefortine C, alternariol, T-2 toxin, and nivalenol. DON (92.9%), aflatoxins (64.3%) and fumonisins (57.1%) were the most prevalent within locally manufactured feeds, while no contamination was found in imported feed. Samples from Kenya were the most contaminated with aflatoxin (maximum 806.9 μg·kg −1 ). The high levels of aflatoxin and trichothecene type A and B contamination found in this study point to potential risks to fish performance and to the health of consumers of the fish and derived products.

On the global scene, aquaculture accounts for about 50% of total fish production amounting to about 80 million metric tonnes. It is estimated that another 40 million metric tonnes of aquatic food will be required by the year 2030. Today, fish farming represents the fastest growing sector of food production. Moreover, aquaculture has a major role to play in the achievement of the first three Sustainable Development Goals on poverty, hunger, food security and healthy lives of people from developing countries. This is significant especially in the developing countries where poverty and malnutrition are a reality. However, in sub-Saharan Africa, per capita fish production from aquaculture is still below world production levels. In Kenya, inland capture fisheries accounted for over 90% of the total national fish production while marine capture fisheries contributed about 5% in the last decade. Kenya has one of the fastest growing human populations in the world indicating that the demand for fish and fish products will continue to rise, increasing the gap between supply and demand. Currently, aquaculture only produces about 24,000 metric tonnes of fish annually compared to an annual average of 178,000 metric tonnes from natural fisheries. The dominant cultured species include: Nile tilapia ( Oreochromis niloticus ), African catfish ( Clarias gariepinus ), rainbow trout ( Onchorhynchus mykis ) and common carp ( Cyprinus carpio ). Culture systems commonly used are static ponds and raceway systems. In addition, the country is endowed with numerous aquaculture resources ranging from favorable climatic conditions to vast water resources. In the year 2009, the Kenyan government took steps to enhance aquaculture production through an Economic Stimulus Programme. This has increased the contribution of aquaculture in Kenya to 11.0% of the total fish production. This paper discusses the growth and development of aquaculture in Kenya during the last 50 years and the impact of government support to the sub-sector. The paper also proposes strategies for ensuring that Kenya becomes one of the leading producers of fish from aquaculture in Africa. Key words : Fish production, capture fisheries, culture systems, Economic Stimulus Programme, aquaculture

This study evaluated the effect of dietary aflatoxin B1 (AFB1) on growth, milt and egg quality in matured Nile tilapia (Oreochromis niloticus). Triplicate groups of Nile tilapia (initial body weight 24.1 ± 2.6 g) were fed with either of four diets (Diets 1 to 4) designed to contain 0, 20, 200 and 2000 μg AFB1 kg−1 diets for 24 weeks. After 24 weeks of AFB1 exposure, growth was significantly (P

Poor culture conditions in low input ponds make fish highly susceptible to infectious pathogens which lead to diseases and mortalities yet the effects of probiotics on immunity, gut microbiota and microbiological quality of fish in low input ponds are unknown. Nile tilapia, Oreochromis niloticus fingerlings (40 g) were randomly stocked at 50 fish m−3 in 1.25 m3 cages in low input ponds. The fish were fed on diets supplemented with either Saccharomyces cerevisiae (1 × 1010 CFU g−1) or Bacillus subtilis (1 × 109 CFU g−1) at six levels: Diet 0 (No probiotic); S. cerevisiae at 2 g kg−1 (Diet 1); 4 g kg−1 (Diet 2) and 6 g kg−1 (Diet 3) and B. subtilis at 5 g kg−1 (Diet 4); 10 g kg−1 (Diet 5) and 15 g kg−1 (Diet 6) for 180 days. Results indicate that hemato-immunological parameters (hemoglobin (Hb), red blood cells (RBC), white blood cells (WBC) serum protein, albumin, globulin and lysozyme activity) were significantly higher in fish fed on probiotic treated diets compared to the control (P < 0.05). On the contrary, fish fed on Diet 6 presented significantly similar Hb and globulin values compared to the control (P > 0.05). Additionally, fish fed on probiotic treated diets retained the probiotics in their guts and lower microbial load was realized in their muscle (P < 0.05). In conclusion, B. subtilis and S. cerevisiae supplementation in diets of Nile tilapia reared in low input ponds improves immunity, manipulates gut microbiota and enhances fish flesh quality.

Black spot disease (diplopstomiasis), an external melanized host inflammatory response caused by a number of digenetic trematode parasites, results in slow growth, deformities and increased mortality among many freshwater fish species globally. We investigated the severity of infection, and genetic parameters for black spot disease among 150 families of Nile tilapia (Oreochromis niloticus) of the Abbassa strain in ponds in Egypt. The causative agent for the black spot disease was identified molecularly as a Uvulifer species using 28S gene. Although 27% of the families remained completely unaffected, the others exhibited signs of black spot infestations randomly distributed in the skin and fins at different levels of severity. Histological examination revealed multiple parasitic cysts surrounded by fibrous capsules with melanin deposits embedded in the muscles. Females were significantly more susceptible than males (P

Three strains of African catfish ( Clarias gariepinus ) from the Netherlands (Dutch), Indonesia and Kenya (Lake Victoria) were studied in hatchery conditions to compare their fecundity, growth performance and survival rates. The results indicated that fecundity was significantly higher ( P < 0.05) in the Kenyan strain (145715.17 eggs Kg -1 ) and lower in the Indonesian strain (86354.55 eggs Kg -1 ). The Indonesian strain had significantly ( P < 0.05) higher final mean body weight, specific growth rate and food conversion ratio. Survival rate was significantly different among the strains ( P

To ensure long-term sustainability of the littoral marine ecosystem for water-based management and aquaculture potential, it is necessary to quantify and project the effect of sea warming on the resident biota. This study evaluated the potential of an oyster Suitability Sites Occurrence Model (SSOM) to predict the status of littoral areas in the future due to sea warming. Data sources comprised Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat 7 ETM +. The suitable sites were ranked on a scale of 1 (least suitable) to 5 (most suitable). In the suitability model, score 5 had the highest proportion (35.8%) of oyster suitability which shrank to 16.2% with a 4 °C increase in sea temperature. Future increases in sea temperature are likely to cause shrinkage in the spatial extent of most suitable and suitable oyster sites. Thus changes in marine oyster suitability in littoral zones are predicted to worsen gradually as sea temperatures increase in the future. Differences in the recorded sea temperature of ≤ 6 °C within and between sites may influence spatial variations in oyster habitat due to future sea warming. Such concepts could form an alternative scientific basis for quantification of potential global climate change effects on biodiversity for marine systems policy adaptation analysis, aquaculture potential, and management.

Egypt is the topmost aquaculture producer in Africa and the third largest tilapia producer globally. Nile tilapia in particular is the cornerstone of fish farming in Egypt. Recently, fish farms have experienced unusual tilapia mortality during summer season, threatening further growth of the sector. In order to understand risk factors, a questionnaire based cross-sectional study was conducted using tilapia epidemiology and health economics online survey tools. We surveyed 113 tilapia farms in four of the largest tilapia producer governorates (Kafr El Sheikh, Beheira, Sharqia, Faiyum) and one governorate with less farming activity (Minya). Farming practices, biosecurity measures and estimated losses were also assessed. Results indicate that a combination of risk factors contributed to the observed mortality events. We observed significant correlation between water source (surface and irrigation canals) and both occurrence and level of unusual mortality events (p

A number of studies have highlighted the promising growth of Egyptian tilapia aquaculture and the role of genetically improved strains in this development, such as the Abbassa Nile tilapia (Oreochromis niloticus, Linneaus, 1758). However, few studies have explored the link between aquaculture development and changes in fish demand among low-income consumers. This study combines household budgeting questionnaires and morphometric tilapia trait rankings conducted in the peak market season of 2017 to examine patterns of tilapia consumption and preferences among low-income women and men consumers across Egypt. Analysis of variance tests and a hierarchical logistic regression model were employed to determine effects of sex, age, educational status, household size, presence of children, food dependency ratio and location on tilapia consumption and trait preferences. Results showed significant differences in tilapia consumption between Lower and Upper Egypt. Greatest heterogeneity in tilapia trait rankings was found in preferences for total body weight, as well as for body width, body length and tilapia head traits. Models predicted that younger women consumers with children in Lower Egypt were more likely to consume smaller tilapia sizes and prefer larger tilapia head traits. This study offers the first evidence base of tilapia trait preferences of low-income consumers to genetic selection programmes considering the adoption of pro-poor and gender-responsive breeding objectives.

The effect of photoperiod (24L:00D, 12L:12D, and 00L:24D) and temperature (22 ± 1°C and 28 ± 1°C) on performance of Clarias gariepinus larvae was tested. Larvae weighing 3.2 ± 0.24 mg were cultured in aquaria at a stocking density of 20 fish L−1 and fed twice a day on catfish starter diet (40% CP) at 10 % BW day−1. Highest mean weight gain (31.00 mg), SGR (7.56% day−1), and survival (83%) were achieved at photoperiod and temperature combination of 00L:24D and 28 ± 1°C. Percent survival of larvae differed significantly (p

A 7-month experiment was carried out to determine the effects of different levels of probiotics (baker's yeast (Saccharomyces cerevisiae) and Bacillus subtilis) on Nile tilapia (Oreochromis niloticus) reared in low input ponds. Monosex male fingerlings (40 g) were randomly distributed into 28, 1.25 m3 net cages at 50 fish m−3 and fed twice daily at 3% body weight on seven isonitrogenous (28% crude protein) diets supplemented with either Saccharomyces cerevisiae (1 × 1010 CFU g−1) or Bacillus subtilis (1 × 109 CFU g−1) at different levels: Diet 0 (control); Diet 1–3 were supplemented with S. cerevisiae at 2 g kg −1 (Diet 1); 4 g kg−1 (Diet 2) and 6 g kg −1 (Diet 3) whereas Diet 4–6 were supplemented with B. subtilis at 5 g kg−1 (Diet 4); 10 g kg−1 (Diet 5) and 15 g kg−1 (Diet 6). Higher final weight (255.31 ± 3.19), Specific Growth rates (SGR) (0.77±0.01) and better Feed Conversion Ratio (FCR) (1.61 ± 0.02) were recorded in fish fed on Diet 2 followed by fish fed on Diet 5. Fish fed on probiotic- supplemented diets had significantly better growth, nutrient utilization and FCR compared to fish fed on the control diet (P < 0.05). Probiotic supplementation significantly affected the body composition of the fish (P < 0.05). S. cerevisiae led to significantly high protein (86.06%) at 4 g kg−1 (Diet 2) (P < 0.05) while B. subtilis led to significantly higher protein (89.40%) at 5 g kg−1 (Diet 4) (P < 0.05). Crude lipid and ash content were significantly lower in the fish fed on probiotic supplemented diets (P < 0.05) compared to the control. This study has demonstrated that the application of probiotics in diets of Nile tilapia in low input ponds promotes growth and enhances body composition. The two probiotics have got different effects depending on the level of application. S. cerevisiae exhibited the best performance at 4 g kg−1 while B. subtilis had the best performance at 10 g kg−1. Keywords: Bacillus subtilis, Nile tilapia, Probiotics, Saccharomyces cerevisiae, Growth, Nutrient utilization

The present study set out to investigate the haematological effects of tobacco leaf dust on African catfish, Clarias gariepinus, fingerlings, with a mean weight of 3.01 ± 1.25 g using “static renewal bioassay system” during a 120-hour bioassay exposure period. Water quality parameters such as pH and dissolved oxygen significantly decreased while total alkalinity and conductivity increased significantly in the exposed media, compared to the control test. Leucocytes counts increased significantly while erythrocytes counts decreased significantly with increasing concentration of tobacco dust. Packed cell volume significantly reduced with increase in the concentration of tobacco dust. Haematological examination showed that there was destruction of the erythrocytes production, and the concentration of haemoglobin was much lower in the exposed fish compared to the control depicting an anaemic condition. The results could provide baseline information for the safe limits of using tobacco leaf dust in fish ponds; hence 1.56 g L−1 concentration of tobacco leaf dust was recommended for pond preparation for Clarias gariepinus fingerling stocking. For better survival rates, the fish should only be introduced in the pond after three days of tobacco application.

Nematodes of the genus Rhabdochona Railliet, 1916, identified as R. paski Baylis, 1928, were collected from the intestine of Hydrocynus forskahlii (Cuvier) (Characiformes: Alestidae), Oreochromis niloticus (Linnaeus) and Tilapia zillii (Gervais) (both Perciformes: Cichlidae) from Lake Turkana, Kenya during 2007–2009. Their morphology was studied in detail using light and scanning electron microscopy. Paratypes of R. paski and museum specimens of R. congolensis Campana-Rouget, 1961 from six other host species were examined for comparison. Based on these studies and the available literature data, Rhabdochona congolensis, R. aegyptiaca El-Nafar & Saoud, 1974 (emend.) and R. vesterae Boomker & Petter, 1993 are considered to be junior synonyms of R. paski. The occurrence of this widely distributed African nematode in many fish species belonging to different families and orders suggests that most of them are probably not definitive hosts of this parasite, but only serve as paratenic, paradefinitive or postcyclic hosts (sensu Odening, 1976). True definitive hosts of R. paski appear to be characiform species belonging to some genera (e.g., Alestes, Brycinus, Hydrocynus) of the family Alestidae.

The main obstacle in developing intensive fish culture is waste management which is detrimental to the environment. To mitigate environmental impacts associated with effluent discharge, measures should be put in place to avoid deterioration of the pond environment. The addition of carbon materials into culture facilities while manipulating the levels of carbon and nitrogen ratios is one of the best strategies of controlling ammonia and nitrite in ponds. This study was carried out in 18 hapas suspended in six, 150 m2 earthen ponds to investigate the effects of C/N ratios (10 and 20) and stocking density (10, 15 and 25 fish m- 2) on water quality, sediment quality and growth of Labeo victorianus. All treatments were carried out in triplicate during a time period of 72 days. A locally formulated and prepared feed containing 30% crude protein with a C/N ratio of 10 was applied. Maize flour was used as the carbohydrate source for manipulating C/N ratio and applied to the water column separately from the feed. Increasing C/N ratio from 10 to 20 reduced (P

The Gastropod Melanoides tuberculatus plays a significant role in hampering fish larval production in earthen ponds. This study investigated use of tobacco waste to assess behavioural and survival responses of M. tuberculatus at different concentrations of tobacco waste solution of 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2 g L 1 . Mean escape time varied significantly among concentrations (P < 0.05). Escape time decreased in 1-, 2- and 3day-old solutions. Percentage survival decreased significantly with increasing concentrations of tobacco waste solution and exposure time (P < 0.05). Concentrations of 1.75 g L 1 and 2.0 g L 1 had high hazard ratios and low survival rates of gastropods and were the most effective in eradication of M. tuberculatus, hence recommended dose for preparing ponds for stocking. We conclude that tobacco waste solution can be used for control of M. tuberculatus.

Survival and physiological response of Labeo victorianus juveniles under varying salinity gradients were studied during a 6 h transport. Salinity ranges were: 0, 0.25, 0.5, 1, 2, 4, 8 and 10 psu. To each transport bag, 100 juvenile L. victorianus (mean weight = 8.0 ± 1.1 g, stocking biomass = 16 kg m − 3 ) were transferred. Water temperature, dissolved oxygen (DO), pH, total ammonia nitrogen (TAN) and carbon dioxide (CO 2 ) were measured before and after transport. Plasma cortisol, blood glucose, plasma sodium, plasma chloride and blood ammonia were also determined. No juvenile mortalities occurred in salinity ranges of 1 to 4 psu. After transport, survival and parameters of physiological response in the juvenile of L. victorianus were significantly different among different salinity treatments (p 2 in water after transport. Plasma cortisol in salinities of 0.5 to 8 psu, blood glucose and blood ammonia in salinities ranging from 1 to 4 psu as well as plasma sodium and plasma chloride in salinity ranging from 1 to 8 psu were similar before and after transport. This study recommends salinity ranges of 1 to 4 psu for minimizing the physiological effects associated with both the primary and secondary physiological response induced by transport stress in juvenile L. victorianus .

The following four species (only females available) of the Philometridae (Nematoda: Dracunculoidea) were recorded from freshwater fishes of Lake Turkana, northwestern Kenya in 2007-2008: Philometra bagri (Khalil, 1965) from the subcutaneous tissue around the mouth, on gill covers and the fin base of the bayad Bagrus bajad (Forsskål) (Bagridae: Siluriformes), Philometra lati sp. n. from the abdominal cavity of the Nile perch Lates niloticus (Linnaeus) (Latidae: Perciformes), Philometra spiriformis sp. n. from capsules on the inner surface of gill covers of L. niloticus and Afrophilometra hydrocyoni (Fahmy, Mandour et El-Nafar, 1976) comb. n. from the fins of Hydrocynus forskahlii (Cuvier) (Alestidae: Characiformes). The new species P. lati is characterized mainly by the presence of distinct oesophageal teeth, absence of large cephalic lobes and caudal projections, and by a combination of other features. Philometra spiriformis differs from all congeners principally in the spirally coiled body and from individual species by a combination of other morphological features. The already known species P. bagri and A. hydrocyoni are redescribed based on light and scanning electron microscopy; findings of both these species in Kenya represent new geographical records.

In Kenya, Nile tilapia (Oreochromis niloticus) is mostly grown in ponds. To avoid excessive reproduction and stunted growth, fingerlings are treated with methyl-testosterone to make all-male populations (monosex). For a national breeding programme that aims to provide genetically improved broodstock to hatcheries that supply monosex fry to smallholder pond farmers, it is important to assess the genetic correlation (rg) for traits between the mixed sex breeding candidates from the breeding nucleus and monosex production fish. The purpose of the study was to estimate genetic parameters for harvest weight (HW), daily growth coefficient (DGC) and body shape and investigate genotype by environment interaction (G × E) for these traits between mixed sex and monosex populations. Forty-eight sires and 76 dams from the F2 generation of a local O. niloticus strain, kept at Sagana Aquaculture Research Station, Kenya were used to produce 76 full-sib families. Mixed sex fry (3 days old) from each full sib family were divided into two groups of 50 individuals each. One group (monosex) was fed a diet treated with methyl-testosterone to induce sex reversal while the other group (mixed sex) was reared on a control diet. After hapa rearing, tagging and weighing, fish were randomly divided and stocked in six earthen ponds, three for mixed sex and three for monosex fish. After 5 months, fish were harvested, photographed and weighed. Genetic parameter estimates for HW, DGC, and shape were obtained on 2105 fish. Heritability estimates for HW, DGC and shape were 0.21 ± 0.03, 0.26 ± 0.04 and 0.12 ± 0.03 for mixed sex respectively. Genetic correlations for HW between monosex and mixed sex was 0.74 ± 0.14, suggesting low G × E. The corresponding rg for DGC and shape were lower; 0.59 ± 0.10, and − 0.19 ± 0.11, respectively, denoting the presence of G × E. It is concluded that G × E between the mixed sex nucleus and monosex production fish is important, and that a breeding programme for Nile tilapia needs to include production performance from monosex siblings. Statement of relevance First study that reports estimates for Genotype by treatment interaction between hormone treated monosex Nile tilapia and mixed sex Nile tilapia, and discusses the consequences for nucleus breeding programmes.

In this study we present estimates of phenotypic and genetic parameters for body size measurements, reproductive traits, and gut length for Nile tilapia (Oreochromis niloticus) selected for growth in fertilized earthen ponds for two generations. Throughout the experiment, ponds were fertilized daily with 50 kg dry matter, (dm)/ha chicken manure. No supplementary feeds were added. For the analysis, 6429 fully pedigreed experimental fish from G0, G1 and G2 were used. Generations were discrete and therefore parameters were estimated separately for each year. Heritability estimates for body measurements ranged from 0.4–0.6 for standard length to 0.69–0.79 for head length. Phenotypic correlations between body weight and body measurements ranged from 0.64 to 0.89. Genetic correlations were close to unity. The heritability estimate for maturity at harvest (corrected for sex) was 0.13. Heritabilities for carcass traits were estimated from G1 only and were 0.16 for gutted weight and 0.06 for dressing percentage. Phenotypic correlation between body weight and gutted weight was 0.84 and the genetic correlation was 0.20. Heritability estimate for gut length was 0.22. We also estimated a high genetic correlation between gut length index and standard length (0.78) but a low genetic correlation between gut length index and body weight (0.22 ± 0.28). These results suggest that selection for growth on an herbivorous diet could result in a correlated response in gut length.

This study investigated the effects of manipulating carbon–nitrogen (C/N) ratio and fish stocking density on pond productivity: total heterotrophic bacteria counts, plankton biovolume and benthic macro-invertebrates. Labeo victorianus juveniles were reared for 72 days in 18 hapas suspended in six ponds measuring 150 m2 at densities of 10, 15 and 25 fish m-2. Fish in hapas received a locally formulated and prepared feed containing 295 g kg-1 crude protein, and ponds were treated with a C/N ratio of either 10 or 20. All treatments were carried out in triplicate. Increasing C/N ratio from 10 to 20 increased phytoplankton by 13% and zooplankton biovolume by 25% in the water column (P

Disease and parasite outbreaks cause mortality of fish, affecting mostly early stages of fish cycle. The outbreaks are usually prevented using a number of chemicals including salt (NaCl) for which protocols are lacking. The purpose of this study was to determine the efficacy of NaCl as a potential prophylactic treatment and its short term toxicity on African catfish (Clarias gariepinus) yolk-sac and swim-up fry during a 24 h exposure period. Three-day-old yolk sac and six-day-old swim-up fry (n = 50 for each stage) were subjected to static bath dip treatment in increasing concentrations of NaCl (0.1, 0.2, 0.4, 0.8, 1.0, 2.0, 4.0, and 10.0 g/L) for 15, 30 and 60 min. Toxic ranges were tested by exposing the fry stages to concentrations of 0.25, 0.5, 0.75, 1.0, 1.25, and 1.50 g/L NaCl for 24 h. Controls were not subjected to any concentration of NaCl. All experiments were executed in triplicate. Regardless of the concentrations and duration of exposure, survival of fish in NaCl treatment differed significantly (P

A new species of dracunculoid nematode, Mexiconema africanum sp. n. (Daniconematidae), is described from the abdominal cavity and the intestine (rarely also the gall bladder) of the catfish Auchenoglanis occidentalis (Valenciennes) (Claroteidae, Siluriformes) from Lake Turkana, Kenya. The new species differs from two other congeners mainly in the absence of two large cell nuclei in the glandular oesophagus, presence of well-developed lateral cephalic elevations, more numerous (14) cephalic papillae and a much longer body of the gravid female (18–22 mm); from Mexiconema cichlasomae Moravec, Vidal and Salgado Maldonado, 1992 also in less numerous (two) caudal processes and a different arrangement of genital papillae in the male. M. africanum is the first representative of the dracunculoid family Daniconematidae described from Africa.

Ascertaining the appropriate selection environment for Nile tilapia (Oreochromis niloticus) in Africa is a critical issue. Two data sets derived from two selection lines originating from a common base population were analysed in this study. The lines were selected in two different input environments, here named ‘low input’ and ‘high input’. Both data sets were combined and jointly analyzed to estimate the phenotypic and genetic parameters, with a special focus on the examination of genotype by environmental interaction. The data sets included a total of 7640 animals with phenotypic information from three discrete generations. Four different models (in terms of fixed effects) were fitted in univariate (harvest weight) and bivariate (harvest weight in each input line treated as two different traits) animal models to estimate variance and covariance components. The heritabilities estimated from the four different models by univariate analyses ranged from 0.15 to 0.41 (all with standard errors of 0.04). The genetic correlations between harvest weights expressed in the two environments, obtained from the bivariate analyses, ranged from 0.74 to 0.84 (with standard error in the range 0.15 to 0.36). We concluded that there was no significant evidence for genotype by environmental interaction for these two particular input environments.

The aim of this study was to quantify the environmental and genetic effects on early growth of Nile tilapia, Oreochromis niloticus, in hapa-in-earthen pond systems. In a pilot study, we grew swim-up fry with or without supplementary feed in hapas suspended in fertilized ponds at 5, 10, 15, and 20 fry/m 2 densities. In the main experiment, we reared swim-up fry from 25 full-sib families separately for 42 days at 15 fry/m 2 density in hapas suspended in two earthen ponds. Hapas were arranged in two column arrays along the sides of the ponds. Ponds were fertilized daily with chicken manure. In addition, fry in one column in each pond were fed twice daily on 40% protein pelleted feed. Results from the pilot study indicated significant effects of stocking density and treatment. In the main experiment, the dietary treatment effect was not significant but there were large differences in growth between ponds. Mean body weight at 42 days was 1.7 g in pond A and 0.4 g in pond B. Fry heritability ( h 2 ) of 42-day fry body weight estimated from the whole data set using a univariate model was 0.01 ± 0.06. The bivariate heritability estimates were 0.59 ± 0.19 in pond A and 0.05 ± 0.11 in pond B. The common environmental/hapa ( c 2 ) effects were 0.14 ± 0.06 and 0.29 ± 0.07 in respective ponds. We found significant positive spatial autocorrelation ( P = 0.02) indicating resemblance in growth of fry in neighboring hapas. Analysis of environmental variables showed that the two ponds differed significantly in dissolved oxygen. The low genetic correlation ( r g = − 0.27 ± 0.69) between body weights of fry in both ponds therefore might suggest genotype by environment interactions for tolerance to low dissolved oxygen in Nile tilapia juveniles.

This study presents results of two generations of selection (G1 and G2) for growth of Nile tilapia. The selection environment consisted of earthen ponds which were fertilized daily with 50 kg dry matter (dm)/ha chicken manure. No supplementary feeds were provided. In total, 6429 fully pedigreed experimental fish were included in the analysis. Survival till harvest was highly variable ranging from 35% to 77% and was affected by initial weight, pond, and age effects. Body weight at harvest (BW) increased from a mean of 67.4 g in the grandparental (unselected) population (G0) to 129.5 g in G2 was affected by initial weight, pond, sex and age effects. Generations were discrete and therefore genetic parameters were estimated separately for each year. Heritability estimates for BW ranged from 0.38 to 0.60, and the heritability for survival ranged from 0.03 to 0.14. The estimated selection response was 23.4 g (34.7%) between G0 and G1 and 13.0 g (14.9%) between G1 and G2. These results demonstrate the feasibility of selection for growth of Nile tilapia in low-input environments.