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Length-weight relationship and condition factor have severalapplications on fish biology, physiology, ecology and fisheries assessment. A six-month study was conducted from November 2013 to April 2014 to determine the length-weight relationship and condition factor of four major cichlids namely Oreochromis niloticus (Nile tilapia), Hemichromis fasciatus (Banded jewelfish), Sarotherodon galilaeus (Mango fish) and Tilapiazillii (Red-belly tilapia) to fill a knowledge gap and provide useful information for fisheries management and conservation in the Golinga reservoir using the length-weight based model. Samples were collected twice every month with gillnets from commercial fishermen. The length-weight relationship had a strong positive correlation (r>0.8) for the four species. Oreochromis niloticus exhibited isometric growth (b = 3.07) whilst Hemichromis fasciatus (b = 2.81), Sarotherodon galilaeus (b = 2.91) and Tilapia zillii (b = 2.75) showed negative allometric growth. Mean condition factor (K) values were greater than one (3.66-4.88) for all the species and varied monthly. The study provided new information on lengthweight parameters for the four cichlids.

Gillnet selectivity is crucial for the effective and sustainable management of fisheries. However, there is inadequate information on gillnet selectivity for commercially important species in Tono Reservoir. To facilitate the sustainable exploitation of fish species, this study was conducted to estimate the selectivity parameters of commonly used monofilament gillnets for commercially important fish species in Tono Reservoir from January 2015 to June 2016. Two common nylon monofilament gillnets used by fishermen in Tono Reservoir with stretched mesh sizes 5 and 7 cm and equal dimensions were placed in the same fishing area and retrieved within 12 h. The fish catches were assessed, and selectivity parameters for Sarotherodon galilaeus, Oreochromis niloticus, Coptodon zillii, Clarias gariepinus and Auchenoglanis occidentalis were estimated using the Holt model. The catch per unit effort of the two gillnets exhibited no significant difference. The optimum total lengths of capture of four fish species excluding C. zillii ranged from 13.53 to 25.43 cm for the 5 cm gillnet, and 18.95 to 35.60 cm for the 7 cm gillnet. Common selection factors varied from 2.71 to 5.09. The mean total length at first sexual maturity for all five fish species ranged from 8.60 to 28.86 cm. Both the 5 and 7 cm gillnets were found to be inappropriate for use in the reservoir. Accordingly, their use should be discouraged to protect juvenile fish so that the sustainable exploitation and conservation of fish species in this multispecies fishery can be achieved.

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Water quality is essential for fish survival and growth in reservoirs. However, little information is known about the water quality status and its relation with fish production in the Tono Reservoir. This study sought to assess water quality parameters and examine association among them as well as determine the correlation between the water quality parameters and fish catch per unit effort of the Tono Reservoir. A three-level stratified sampling was adopted and samples were collected on a monthly basis. Water quality parameters such as water level, temperature, pH, electrical conductivity, transparency, turbidity, dissolved oxygen, chloride, sulphate, phosphate-phosphorus, silica, nitrate-nitrogen, nitritenitrogen, chlorophyll-a, and fish catches were measured simultaneously from each of the three strata of the reservoir. The water quality parameters of the reservoir fell within the recommended range for fish production. Concentrations of water quality parameters for the riverine, transitional and lacustrine zones showed no significant difference (p > 0.05). Catch per unit effort correlated significantly positive with only chloride (r ¼ 0.61, p < 0.05) attributable to fertilisers used on surrounding farm lands and carried by runoff or floods to the reservoir. The reservoir could be classified as mesotrophic based on chlorophyll-a concentration. It was recommended that the reservoir water quality should be monitored quarterly by the Ministry of Fisheries and Aquaculture Development to ensure safe fish production.