Length–Weight Relationship, Condition Factor and Maturity Characteristics of an Invasive Oreochromis niloticus (Cichlidae) in an Alkaline-Saline Lake Nakuru, Kenya

Studies on the length–weight relationship (LWR), condition factor (K) and size at first maturity status are important aspects of fish biology and fisheries management. Although many studies have reported about growth parameters of Oreochromis niloticus under various fishery waters and aquaculture systems, a recent invasion of the species in Lake Nakuru (Kenya) is a new case study. Therefore, this paper provides baseline data on LWR, K and Lm₅₀ of O. niloticus in relation to limnological conditions in the lake. Water quality parameters (pH, temperature, conductivity, dissolved oxygen, salinity and total suspended solids) and indicators of eutrophication status (phosphates, nitrates and chlorophyll-a.) were analysed in November 2020 and November 2021. Fish samples were collected using experimental gillnets with assorted mesh sizes from 2 to 4 in., and their morphometric data was analysed. Results show significant spatial variations (ANOVA; p < 0.05) in all the water quality parameters. These parameters, except the temperature, also significantly differed between the study periods (t-test; p < 0.05). O. niloticus was the most dominant species, comprising 75.3% and 90.8%, in 2020 and 2021, respectively. Mean total length (19.80 cm) and weight (169 g) of the fish in 2021 were greater than 19.20 cm and 153 g in 2020. Nile tilapia exhibited an isometric LWR (b = 3), better well-being (K>1), but it matured at smaller sizes (<25 cm) in both sexes. Further monitoring of water quality changes in Lake Nakuru and their future impact on the population of O. niloticus is recommended.