Dynamics of the population and biotic potentials of Aphyosemion gardneri (Boulenger, 1911) (Cyprinodontiformes: Aplocheilidae) in a Nigerian rainforest pond

Abstract

The Population dynamics and biotic potential of Aphyosemion gardneri (Boulenger, 1911) were studied for twelve months in Mfangmfang Pond, an artificial rainforest pond in Uyo, Niger Delta, Nigeria using timed pond net catches as proxies of natural ecological population changes. The fish habitat was the air-water interface of the pond epipelagic zone of the vegetated littoral margin. The fish maintained a perennial population in the pond as shown by its occurrence in catches throughout the 12 months of the year. The catch abundance varied broadly (c. 18 – fold) from a minimum N_min =16 in November to a maximum N_max = 284 in May. The monthly mean catch was N_mean = 103. Monthly catch abundance was significantly correlated with habitat Phenological parameters (rainfall, air temperature, mean evaporation rate and photoperiod), Hydrophysical parameters (water level and transparency) and Hydrochemical parameters (dissolved oxygen concentration, free carbon dioxide, total alkalinity, total hardness, pH and conductivity). It is inferred that the pond's environmental factors contributed significantly to the observed population changes. A. gardneri attained a maximum total length of 55mm in Mfangmfang Pond. The length growth impetus was low at 0.33mm mo^-1, thus resulting in a relatively high longevity estimate of T_max = 14 yrs. The body size–catch abundance functions suggest the existence of a size-structured population. Monthly biotic potential (r_max 1 mo^-1) and yearly biotic potential (rmax 2, yr-1) were computed for this A. gardneri population. Values of r_max 1 varied from a minimum of -1.881mo^-1 in October to a maximum of + 1.960 mo^-1 in May. Annual mean value was + 0.924 mo^-1. Monthly values were significantly pond-level correlated with pond Limnological parameters, (surface temperature, dissolved oxygen concentration, and pH). The yearly biotic potential varied from a minimum of r_max 2 = -22.572 yr^-1 in October to a maximum of r_max2 = 23.520yr^-1 in May (mean r_max 2 = + 0.0686 yr^-1). The January – December biotic potential estimates (r_max 1 = +0.895 mo^-1; r_max 2 = + + 10.740 yr^-1) indicate a moderately high population increase over the year, a trait which probably ensures population resilience and survival despite variations in environmental attributes.