Sizes, condition factors and sex ratios of the scattered populations of the small cichlid fish, Alcolapia grahami, that inhabits the lagoons and sites of Lake Magadi (Kenya), one of the most extreme aquatic habitat on Earth

Abstract

Alcolapia grahami is a small cichlid fish that inhabits the scattered lagoons and sites of Lake Magadi (Kenya). Exceptional physiological, morphological, biochemical and behavioural adaptations allow the fish to tolerate the harsh environmental conditions that exist in the locations, the most extreme milieus occupied by a species of fish on Earth. The temperature of the water is inordinately high for a fish; large diurnal fluctuations in the levels of the partial pressure of oxygen occur, with acute hypoxia happening during the night and hyperoxia during the day; the salinity of the water is ~60% of that of seawater and; the pH may be as high as 11. Having an average adult body length of less than 6 cm and a body mass of ~5 g, the fish is very small in size. Here, body mass, body length, condition factors (CFs) and sex ratios (SRs) were determined on fish sampled from nine accessible isolated populations. Except for the Cement Water Holding Tanks (CWHT) population, where the female-to-male SR was 4:1, overall, the number of male fish surpassed the female ones by a ratio of ~2:1. The male fish were heavier and longer compared to the female ones. The relatively lower ambient temperature in the CWHT (32 °C) may explain the female dominated population and the effect future increase in temperature may have on sex distribution in the various populations of A. grahami. In fish from the Fish Spring Lagoons B and D, the CFs were greater in the male fish relative to the female ones. Exhibiting poor-to-fair body states, the CFs of the different populations of A. grahami, that ranged from 1.1. to 1.8, were among the lowest that have been reported in fish living under natural setting. The skewed SRs and the markedly low CFs of A. grahami reported here may be ascribed to the harsh (stressful) environmental conditions the fish contends with. The values may signal prospective demise of the fish. Conservation measures are urgently needed to protect a very rare fish.