Water samples for physico-chemical analysis for this study were collected monthly for five years between April 2008 and March 2013. Conductivity, temperature, dissolved oxygen and pH was measured in situ using a Surveyor II model hydrolab. Chlorophyll-a concentration was determined using a Genesys 10S Vis spectrophotomer. Nutrients were determined using standard methods and procedures. Analysis of Variance (ANOVA) was used to determine spatial and temporal variation in physicochemical and biological factors. Principal component analysis (PCA) was performed to establish the correlation of the physico-chemical and biological parameters among sampling stations and to group stations with similar physico-chemical parameters. Both spatial and temporal significant variations (P < 0.05) were detected in the concentrations of the nutrients measured during the study.

Comparative growth performance of male monosex and mixed sex Nile tilapia (Oreochromis niloticus) was conducted in six earthen ponds each measuring 150 m 2 at the Kenya Marine & Fisheries Research Institute (KM-FRI), Kegati Aquaculture Research Station. Male monosex and mixed sex of O. niloticus juveniles at an average weight of 12.2 ± 0.02 g and average length of 7.6 ± 0.02 cm were collected from nursery production ponds. The male monosex juveniles were obtained by feeding newly hatched juveniles with feed dosed with 17--methyltestosterone hormone for a period of one month. Stocking was at 3 juvenile m -2 and feeding was carried out using 28% crude protein diet twice daily for six months at 4% body weight. Selected water quality parameters (dissolved oxygen, temperature, pH, electrical conductivity and total ammonia nitrogen) were measured weekly in situ, while sampling for weight and length measurements was conducted on a monthly basis for a period of six months. Specific Growth Rate (SGR), Feed Conversion Ratio (FCR), Condition Factor (CF) and survival rate (%) were measured at the end of six months. Data were subjected to one-way analysis of variance (ANOVA). At the end of six months, the average weight of male monosex and mixed sex fishes was 200.8 ± 0.81 g (mean ± SE) and 123.4 ± 0.76 g, respectively, while the average length of male monosex and mixed sex was 22.4 ± 0.21 cm and 18.6 ± 0.23 cm, respectively. The male monosex O. niloticus achieved significantly increased final weight and length, SGR, FCR and CF than the mixed sex O. niloticus (p < 0.05). However, both male monosex and mixed sex fish recorded similar survival rates (p > 0.05). There were no significant differences in mean water quality parameters in male monosex and mixed sex ponds (p > 0.05). The male monosex fish performed better because most energy was spent on muscle and tissue development while the mixed sex fish spent most energy on reproduction activities at the expense of muscle and tissue development. Further studies should be done in other culture systems such as liner ponds, tanks, cages and raceways. How to Cite

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African carp, Labeo victorianus, is one of the threatened endemic fishes of Lake Victoria which requires conservation and has potential for aquaculture. We conducted a series of experiments on L. victorianus aiming at producing juveniles for both human consumption and stock enhancement. A total of 79 broodstock (mean body weight = 227.06 g) were collected from the wild; packed at 200, 300, and 500 g/L; and transported by road for 7 h. All fish survived during transportation whereas dissolved oxygen decreased and total ammonia nitrogen increased significantly after transport. Females produced 46,702–86,712 eggs (mean = 68,189 ± 2397) and fecundity was highly correlated with the fish body size (R2 = 0.96). Only males re‐spawned in captivity while females did not. At 28 C, females spawned 11–12 h after pairing with males. Larvae can either be fed with formulated diet or natural zooplankton. Juveniles (mean length = 36.7 mm; mean body weight = 0.46 g) can be packed as high as 60 fish/L and transported by road for 12 h with low mortality (2.7–10.3%). These results show that captive breeding of L. victorianus can be a good strategy to produce juveniles to boost wild population as well as a source of seeds for culture.

Abstract:In the present study, anaesthetic effects of different sizes (5, 10, 15, 20, 25, 30, 35 and 40g) of African catfish (Clarias gariepinus) juveniles was investigated at different concentrations (0/control, 10, 15, 20, 25, 30, 35, 40, 45, 50 g/L) of sodium bicarbonate. Juveniles were bath immersed in each of the different concentrations of sodium bicarbonate solution for 5 minutes and recovery times in clean aerated water was established. Juveniles took between 0.67 to 5.44 minutes to reach full anaesthesia and 0.66 to 4.25 minutes to recover fully from anaesthesia. An inverse exponential relationship was observed between sodium bicarbonate concentrations and induction time, whereas exponential relationship was observed between sodium bicarbonate concentrations and recovery time. Size of C. gariepinus juveniles significantly affected the induction time (P < 0.05) with smaller juveniles getting to full anaesthesia faster than bigger juveniles at the same concentration of sodium bicarbonate. In addition, recovery time was size dependent where smaller C. gariepinus juveniles took significantly longer time (P < 0.05) to recover from anaesthesia than bigger juveniles. All juveniles reached anaesthesia and recovered in less than 5 minutes except for 30 g juveniles at 15g/L of sodium bicarbonate which was anaesthetized at 5.44 minutes.