Sex distributions and condition factors of the fragmented populations of the Lake Magadi cichlid fish, Alcolapia grahami: A fish living under extreme environmental and anthropogenic selective pressures

Alcolapia grahami a small cichlid fish which subsists in scattered lagoons of Greater Lake Magadi (GLM) and Little Lake Magadi (LLM) which are located in a highly tectonically active part of the eastern arm of the Great... [ view full abstract ]

Alcolapia grahami a small cichlid fish which subsists in scattered lagoons of Greater Lake Magadi (GLM) and Little Lake Magadi (LLM) which are located in a highly tectonically active part of the eastern arm of the Great Rift Valley of Kenya. To enable the fish to tolerate severe environmental conditions which include high water temperature (42ªC), large diurnal shifts in oxygen availability in the water and high alkalinity (pH ~10), exceptional physiological, morphological and behavioral adaptations have developed. Among others, these include highly specialized gills for gas exchange, osmoregulation and uncharacteristic of fish, excretion of products of nitrogen metabolism entirely as urea. Sex ratios (SRs) and condition factors (K) of different populations of the fish were investigated in order to assess the stress the fish has contended with and is still living under. Except for the Water-Holding Tanks, where females exceeded males at a ratio of 4:1, in the other lagoons of the GLM and in LLM, the numbers of male fish surpassed the female ones, with the male-to-female SRs ranging from 1.4:1 to 19:1. The sex bias of the fish populations correlated with the environmental severities of the lagoons. The overall mean K for A. grahami was 1.46. Signifying a fish in very poor body condition, it (the K) is one of the lowest values that has been reported in fish living under natural conditions. The adverse environmental conditions which the fish subsists under may largely explain the state the fish is in. Presently, survival of the fish is directly threatened by humans activities such as sinking boreholes close to the Lake, actions which will reduce the recharge of the lagoons from the underground water; bathing in the lagoons, an activity which introduces pollutants like heavy metal pollutants into the water, and; siltation of the lagoons from soil erosion, resulting from poor agricultural practices around the Lake. Urgent conservation measures of a unique fish which offers rare glimpse into the astounding degree to which animals can adapt to harsh environmental conditions and one which an appropriate model of the effects of global warming on animal life are urgently required.