On-farm trials with rice fish cultivation in the west Kano rice irrigation scheme, Kenya

The viability of integrating rice farming with fish culture was studied in ten (10) rice plots. The on-farm research was done during one rice-growing season starting May 2003. The rice variety used was IR 2793-80-1 while the fish species was the Nile tilapia, Oreochromis niloticus. The fish culture period lasted 77 days. An average fish production of 132.4 kg/ha was obtained. The mean recovery rate of tilapia was 43 per cent. Total rice yield from the fields stocked with fish was lower than from unstocked fields. The net returns were not significantly different

Comparative study of hatching rates of African catfish (Clarias gariepinus Burchell 1822) eggs on different substrates

The hatching rates of African catfish (Clarias gariepinus) eggs on four natural substrates: the roots of Nile cabbage (Pistia stratiotes), water hyacinth (Eichhornia crassipes), pond weed (Ceratophyllum dermasum) and green grass leaves (Commelina sp.), and four artificial substrates: sisal mats, nylon mats, papyrus mats and kakaban mats, was assessed. Concrete slabs were used as control. The natural substrates performed better than the artificial ones. Pistia roots gave the best mean hatching rate of 66.2 ± 3.62%. Green grass leaves were second with a mean rate of 54.0 ± 3.46%, water hyacinth was third with 49.7 ± 3.16% and Ceratophyllum fourth with a mean of 13.0 ± 2.37%. Concrete slabs gave a mean rate of 18.6 ± 2.8%, sisal mats 18.6 ± 2.0%, papyrus 12.2 ± 1.2% and kakaban 11.8 ± 1.9%. Nylon mats were the last, with a mean rate of 4.0 ± 0.7%. The best performing natural substrates were those with the ability to float and thin fibrous roots that seemed to allow higher aeration of the eggs during incubation. The cost of using natural substrates was minimal

Comparative study of hatching rates of African catfish (Clarias gariepinus Burchell 1822) eggs on different substrates

The hatching rates of African catfish (Clarias gariepinus) eggs on four natural substrates: the roots of Nile cabbage (Pistia stratiotes), water hyacinth (Eichhornia crassipes), pond weed (Ceratophyllum dermasum) and green grass leaves (Commelina sp.), and four artificial substrates: sisal mats, nylon mats, papyrus mats and kakaban mats, was assessed. Concrete slabs were used as control. The natural substrates performed better than the artificial ones. Pistia roots gave the best mean hatching rate of 66.2 ± 3.62%. Green grass leaves were second with a mean rate of 54.0 ± 3.46%, water hyacinth was third with 49.7 ± 3.16% and Ceratophyllum fourth with a mean of 13.0 ± 2.37%. Concrete slabs gave a mean rate of 18.6 ± 2.8%, sisal mats 18.6 ± 2.0%, papyrus 12.2 ± 1.2% and kakaban 11.8 ± 1.9%. Nylon mats were the last, with a mean rate of 4.0 ± 0.7%. The best performing natural substrates were those with the ability to float and thin fibrous roots that seemed to allow higher aeration of the eggs during incubation. The cost of using natural substrates was minimal.Hatching, Seed production, Fish eggs, Africa, Kenya, Clarias gariepinus

Effects of cultivation techniques on the characteristics of cysts from a salina in Kenya

Cysts produced after inoculation with San Francisco Bay (SFB) strain Artemia were harvested and analysed at Artemia Reference Centre. Results obtained after nutritional analysis indicate a potential source of high quality cysts. Cyst hatching percentage, hatching rate and hatching efficiency was 61%, 24h and 173,400n/g respectively. Hatching percentage (H%) varied slightly with variation in salinity and peroxide treatment. Highly unsaturated fatty acids (HUFA) content was representative of high quality cysts. This was also supported by the good growth performance in test with the marine Mysid, M. bahia M

Does African catfish (Clarias gariepinus) affect rice in integrated rice-fish culture in Lake Victoria Basin, Kenya?

An experiment was conducted for 98 days in the Lake Victoria Basin to investigate the interactions of fish and rice growth performance in rice paddies. The experiment was laid out in a split-plot design, with rice cultivar as the main plot and method of rice-fish culture as the sub-plot. Treatments consisted of two levels of rice-fish culture and three cultivars of rice. Rice cultivars used were; ITA, BR 11 and IR 2793-80-1 obtained from the National Irrigation Board (NIB), Kenya. Clarias gariepinus, (15 ± 0.4 g) were stocked at 6 m-2 and given supplementary diet containing 35% crude protein and 7% lipids at 2× maintenance level. There was significantly less incidence of stem-borers in rice-fish polyculture compared to rice monoculture (P< 0.05). Rice-fish polyculture gave significantly higher rice yield than rice monoculture (453 ± 1.0 gm-2). The seed yield differed significantly (P< 0.05) between the rice cultivars with ITA giving the highest yield followed by IR and BR. There were significant differences in growth performance of C. gariepinus in the treatments (F = 4.518,df = 2, P = 0.014) with best growth recorded in the Fish-ITA and least in Fish-BR. Mean net annualized fish production was highest (3,767 ± 300 Kgha-1yr-1) in the ITA-Fish plots with no statistical differences recorded between BR-Fish and IRFish plots. Fish survival ranged from 79.9 to 82.6 percent in Fish-IR, Fish-BR and Fish-ITA respectively.Key words: African catfish, rice-fish culture, rice yield, fish yield

Alongshore distribution and abundance of fish larvae off the coast of Kenya

Knowledge is limited on the fish larval assemblage in shallow lagoonal reefs along the Kenyan coast. Fish larvae from five lagoons, spanning 120 km on the Kenyan coast, were sampled in March 2007 and April 2008 to compare interannual spatial variations in species composition, abundance and diversity along the coast. In all, 2 644 fish larvae were sampled, comprising 26 families and 37 species in 2007 and 43 families and 73 species in 2008. The larval assemblage was dominated by Gobiidae, Blenniidae, Pomacentridae and Gerreidae during both years. Larvae hatched from non-pelagic mode of spawning constituting 92% of total numbers. Mean larval abundance (no. 100 m–3 ± SE) along the coast ranged from 5.0 ± 1.0 to 414 ± 226, with highest densities occurring on the northern sites of Watamu (414 ± 226) and Malindi (31 ± 10). Interannual variation in larval abundance between 2007 (2.17 ± 0.3) and 2008 (2.16 ± 0.1) was not significant (p > 0.05). Shannon-Wiener species diversities between sites ranged from 1.2 ± 0.4 to 2.3 ± 0.3, with highest diversities occurring in Mombasa (2.2 ± 0.5) and Nyali (2.3 ± 0.3). In 2007, the occurrence of preflexion larvae increased northwards from Mombasa (18.2%) to Watamu (86.4%), whereas in 2008, the reverse was the case with the incidence of preflexion larvae reducing northwards from Mombasa Marine Park (76%) to Watamu Marine Park (2%). These trends indicate interannual variation in larval source sites for fish species. Correspondence analysis revealed distinct larval assemblages at sites along the coast, which varied between years. Keywords: abundance, alongshore, diversity, fish larval assemblages, reef lagoonsAfrican Journal of Marine Science 2010, 32(3): 581–58

Evaluation of sodium chloride (NaCl) for potential prophylactic treatment and its short-term toxicity to African catfish Clarias gariepinus (Burchell 1822) yolk-sac and swim-up fry

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 <0.05) from the untreated controls. Effective concentration ranges of NaCl were 0.2–0.8 g/L and 0.2–1.0 g/L in the yolk sac and swim-up fry respectively at exposure duration of 15 min. No fry survival was recorded at a concentration of 10.0 g/L for either stage of development. The mean 24 h LC50 values for the yolk sac and swim-up fry were 0.61 and 0.70 g/L NaCl respectively. Sodium chloride may be used as prophylactic treatment in early stages of C. gariepinus but could be toxic at longer exposure times. However, empirical tests on efficacy of NaCl on pathogens are recommended

Microbiome diversity in Diaphorina citri populations from Kenya and Tanzania shows links to China.

The Asian citrus psyllid (Diaphorina citri) is a key pest of Citrus spp. worldwide, as it acts as a vector for "Candidatus Liberibacter asiaticus (Las)", the bacterial pathogen associated with the destructive Huanglongbing (HLB) disease. Recent detection of D. citri in Africa and reports of Las-associated HLB in Ethiopia suggest that the citrus industry on the continent is under imminent threat. Endosymbionts and gut bacteria play key roles in the biology of arthropods, especially with regards to vector-pathogen interactions and resistance to antibiotics. Thus, we aim to profile the bacterial genera and to identify antibiotic resistance genes within the microbiome of different populations worldwide of D. citri. The metagenome of D. citri was sequenced using the Oxford Nanopore full-length 16S metagenomics protocol, and the "What's in my pot" (WIMP) analysis pipeline. Microbial diversity within and between D. citri populations was assessed, and antibiotic resistance genes were identified using the WIMP-ARMA workflow. The most abundant genera were key endosymbionts of D. citri ("Candidatus Carsonella", "Candidatus Profftella", and Wolbachia). The Shannon diversity index showed that D. citri from Tanzania had the highest diversity of bacterial genera (1.92), and D. citri from China had the lowest (1.34). The Bray-Curtis dissimilarity showed that China and Kenya represented the most diverged populations, while the populations from Kenya and Tanzania were the least diverged. The WIMP-ARMA analyses generated 48 CARD genes from 13 bacterial species in each of the populations. Spectinomycin resistance genes were the most frequently found, with an average of 65.98% in all the populations. These findings add to the knowledge on the diversity of the African D. citri populations and the probable introduction source of the psyllid in these African countries