GROWTH PATTERNS AND CONDITION FACTORS OF FOUR DOMINANT FISH SPECIES IN LAKE ONA, SOUTHERN NIGERIA
Ekelemu, K. Jerimoth and Samuel, A. A. Zelibe
Department of Fisheries Science
Delta State University, Asaba, Nigeria
Email: jerimothekelemu@yahoo.com
ABSTRACT
Growth patterns involving evaluation of Length-Weight Relationships (LWR) of four dominant fish species in Lake Ona, Southern Nigeria, were studied. The fish species, Heterotis niloticus (Osteoglossidae), Syndontis nigrita (Mochokidae), Citharinus citharus (Citharinidae) and Heterobranchus bidorsalis (Clariidae) were caught from 2001 to 2003, using varied fishing gears. The gears were-three bottom set and three surface set gill nets of mesh sizes 1.0, 3.0 and 5.0 cm, with each having a length of 25.0m and a depth of 3.0m; cast net with stretched mesh size of 6.4cm; fish baskets, locally called manly; non-return value traps and a set of long-lines of length 35.0m while Fish Aggregating Devices (FAD) and fences were equally used to aggregate fishes. The LWR was determined from the formula, w= aLb with the parameters a and b in that formula estimated through logarithmic transformation in the form of Log W = Log a + bLog L. The condition factor (k) was estimated from the relationship, k = W100/L3. The results obtained from LWR are presented for the four species and the values of the growth exponent “b”ranged from 1.92 to 3.04 for H. bidorsalis; 2.47 t0 3.03 for H. nitoticus; 1.39 to 2.11 for C. citharus and 1.01 to 1.97 for S. nigrita. Fish species in the lake were generally healthy and in good condition. Overall mean condition factor (k) were 1.21 for H. bidorsalis; 1.57 for H. miloticus; 2.40 for C. citharus and 1.60 for S.nigrita.
Keywords: Length-weight relationship, Condition factor, Growth exponent, Isometric-allometric growth patterns, Lake Ona.