Department of Environmental Studies

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    REPRODUCTIVE PERFORMANCE OF NATURALIZED RAINBOW TROUT (Oncorhynchus mykiss, WALBAUM 1792) FROM SAGANA COLD WATER STREAM AND IMPLICATION ON FRY PRODUCTION FOR AQUACULTURE DEVELOPMENT IN KENYA
    (Karatina university, 2023-10) Njue, Justus Nyaga
    Naturalized rainbow trout (Oncorhynchus mykiss) populations form important recreational fishing resource in the world. Globally, rainbow trout is among the most widely introduced fish species and has been translocated outside its native home range, into at least 99 countries including the tropical regions where it has established naturalized populations. Information on the performance of the hatchery and wild populations of O. mykiss following spawning interactions has not been adequately explored especially in the tropical environments. The current study aimed at evaluating the spawning interactions between naturalized and wild O. mykiss from the high altitude second order stream, the Sagana in Kenya. Spawning and incubation were performed under controlled conditions in a hatchery facility to assess their performance. In each spawning process, total length, weight, condition factor and fecundity of the brooders were recorded. Fertilization rate, hatchability and survival of the fry were determined. Egg diameters were modelled as a function of biometric and reproduction parameters, using generalized linear model. Total fecundity of the broodstock differed significantly among the wild strain, hatchery reared and the cross between hatchery and wild stock (F = 8.934, df = 2, P = 0.0045). The fecundity of the broodstock varied with the average weight of the brooders where brooders with high average weight had a high fecundity. Relative fecundity was significantly different among the three groups of fish (F = 6.134, df = 2, P = 0.0217) but the differences between the hatchery and cross strain of wild and hatchery fish were not significant. Fertilization rate showed significant differences among fish in the three experimental groups (F = 10.136, df = 2, P = 0.0057), Eyed egg survival was lowest among the wild fish but showed no significant differences between the hatchery and cross between wild and hatchery strains. The study recommends the use of hatchery and wild crossed fish to support fry production for use in subsequent restocking of all trout streams in the country. Based on this study, management strategies involving restoration of trout population that would benefit anglers without reliance on importation of eyed eggs are recommended.
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    GROWTH PERFORMANCE OF RABBITFISH (Siganus sutor) REARED IN BRACKISH WATER EARTHEN PONDS, OFFERED BLACK SOLDIER FLY (BSF) LARVAE (Hermetia illucens)
    (Karatina University, 2022-11) OKEMWA, DOUGLAS MINYONGA
    The trend in mariculture development in Kenya is rising as the population and the demand for food increases. Rabbitfish (Siganus sutor) is a suitable candidate for mariculture in Kenya since it can be raised in ponds, accepts formulated feeds, and has a better growth performance as compared to other marine finfishes. It is also acceptable to local and international consumers and thus will have no marketing problem. Currently, S. sutor is the most targeted species and heavily fished on the Kenyan coast and Mariculture would increase its availability and sustainability. This study presents a 90 day’s first trial on the growth performance of S.sutor fed on black soldier fly meal in brackish water environment on the north coast in Kenya earthen ponds (hapa nets). The study had a complete block randomized design (CBRD) with four treatments, which were performed in triplicates and assigned randomly among twelve hapa net cages set in three rows (black nylon, sized (#1mm) and 1.5 x 1.0 x 1.2 meters). S.sutor were stocked at 15/fish/hapa and fed twice a day (0900HRS and 01600HRS) at 5% body weight throughout the study period. The cages were allocated treatments randomly as, T1 100% black soldier fly larvae, 0% fish meal, T2 25% fish meal replaced with 75% black soldier fly larvae), T3 50% fish meal was replaced with 50% BSFL and T4 was used as a control (40% commercial feed). Sampling was done monthly for total length (cm) and weight (g). The results showed that 100% BSFL feed had the highest initial mean weight of 36.06±0.99g, 40% commercial feed had the lowest at 33.76±0.68g. The highest final mean weight was observed in T1, (100% BSFL) at 68.36±0.42 and T2, (25% fish meal 75% BSFL) the lowest at 57.28±0.33g. Feed conversion ratio (FCR) in all diets and growth performance among the different treatments had no significant difference (p<0.05) at (F=6.9122, df=3, p<0.05). The water temperatures, pH, salinity, dissolved oxygen (DO), nitrogen (NH3-N), Nitrites - nitrogen (NO2-N) and total ammonia (NH3-N) values in all treatments were within the optimal limits for S. sutor growth. The study reports useful information on the growth performance and survival of S.sutor fed on black soldier fly larval diet. These findings, from this study revealed that S. sutor is suitable for culturing in brackish waters and the community can easily benefit from the species and act as food security and provide an alternative source of income for rural communities.
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