Studies on size distribution of skipjack tuna (Katsuwonus pelamis): effect on chemical composition and implications for its utilization

Size and composition of skipjack tuna in Nigeria's Exclusive Economic Zone were investigated between May 1982 and January 1983. Monthly average length ± standard deviation varied between 41.65 ± 2.64 cm in January 1983 and 46.60 ± 3.02 cm in September 1982. Corresponding average weight varied between 1.34 ± 0.18 and 1.90 ± 0.37 kg. After logarithmic transformation of the variables (length and weight), a correlation coefficient of 0.901 was obtained. Frequency distribution of length classes enabled three size groups (small, medium and large) to be distinguished. Moisture, protein and ash content of fillets were not significantly affected by the size of the fish, but lipid content increased significantly ( P < 0.05) with size. Widest variations were observed in salt content, which decreased significantly ( P < 0.05) with increase in size. All chemical components were significantly affected ( P < 0.05) by seasonal variation. The implications for the fishery and utilization of this resource are discussed.