Aspects of the biology of snakehead, Parachanna obscura (Gunther 1861) in the Cross River, Nigeria.

摘要

Study on some aspects of the biology of snakehead, Parachanna obscura, in the Cross River System was conducted from January to December, 2009, to analyze the food and feeding habits, sex ratio, size frequency and length-weight relationship of the species. Food and feeding habit were determined using frequency of occurrence, numerical and point methods. A total of 330 specimens were studied during the period, consisting of 135 (40.9) males, and 195 (59.1) females. Analysis of food items showed that P. obscura is an omnivorous species that feeds mainly on fish, insects, other invertebrates and plant materials. Whole fish and fish parts were the most important food items of P. obscura on the basis of frequency of occurrence, numerical and point methods while whole insects and insect parts ranked second followed by plant materials. 62.4 of the stomach contained food while 37.6 were empty. Highest feeding intensity was observed in the month of July - GRI=70 and lowest in the month of May - GRI=42.9. There was no variation in the gut repletion index of the dry and wet season; both had a GRI of 62.4 respectively. Feeding intensity was also higher in female (GRI=36.1) than male (GRI=26.4). The food composition of P. obscura did not show any variation with sex and season. The study also showed that females were more abundant than the males with a sex ratio of 1:1.4. Length-weight relationship of P. obscura indicates a negative allometric growth with b=2.75 and a=0.0014. The uncomplicated and flexible feeding strategy of P. obscura makes it a good culture species for ponds if fed with compounded feed of plant and animal origin.