ABSTRACT
Thirty specimens of Heterotis niloticus were procured from both the wild and the open fish market, to investigate the possible identification of external body features that will differentiate the sexes of this commercially important fish species.
External measurements, which include the dorsal length, the pre-dorsal length, the head length, the peduncle length, the anal length, the pectoral length, the pelvic length and the caudal length, were made. Ratios of these external length measurements to the standard length were calculated and analyzed. In addition, the ratios of the inter-orbital length of head length and the snout length of head length were also analyzed. The sexes of the specimens were determined by both gross and histological examination of the gonads.
The result of this study showed that only two of the morphological ratios namely peduncle length of the standard length and the inter-orbital length of the head length had significantly higher values (P<0.05) in the females. The peduncle length of the standard length in the female is 5.13 ± 0.56 as against 4.89 ± 0.43 recorded in the male, while the inter-orbital length of the head length in the female is 39.35 ± 2.16 as against 37.54 ± 2.05 recorded in the male. Furthermore, sensory pits count on both the right and the left opercula plates were higher in the male than the female. Mean count of 10.29 ± 2.87 on the right, and 10.00 ± 1.00 on the left opercula plates were recorded for the male specimen, while 9.93 ± 1.33 and 9.8 ± 1.15 were recorded on the right and the left opercula plates of the female respectively. However, the differences observed in the sensory pit counts were not significant (P>0.05).
This study showed that the peduncle length and inter-orbital length are longer in the female than in the male of H. niloticus, and are therefore sexually dimorphic characters.
