SOME ASPECTS OF THE BIOLOGY AND TAXONOMY OF RABBITFISHES (FAMILY: SIGANIDAE) FROM KENYAN INSHORE MARINE WATERS

Abstract

Rabbitfishes (Siganidae) are valuable commercial species in many parts of the world. Along the East African coast, they constitute important food and commercial marine fish resources. However information on their biology and taxonomy is scanty. Therefore this study was aimed at bridging the knowledge gap on their taxonomy and distribution. Data was collected on rabbitfish specimens landed at six (6) landing sites along the Kenya coast. Morpho-meristic measurements and counts were made on 234 specimens. A total of six (6) species: Siganus canaliculatus, S. sutor, S. stellatus, S. luridus, S. rivulatus and S. argenteus were recorded. Msambweni landing site recorded all the 6 species, followed by Shimoni and Malindi with 5 each, then Kilifi with 4 while Mombasa and Vanga with only 3 species. In the present study S. stellatus had the highest mean length (SL), body depth (BD), dorsal fin base length (DFbL) and anal fin base length (AFbL). Siganus luridus had the lowest mean SL, BD, DFbL and AFbL. The morphometric data was subjected to Principal Component Analysis (PCA) in PaST software programme. Characters identified in the PCA to contribute to most of the variation were subjected to the non-parametric Mann-Whitney U-test at α < 0.05. PCA results showed clear separation of polygons for two species S. stellatus and S. luridus with S. luridus specimens in the positive part of 2nd PC and S. stellatus specimens in the positive part of 1st PC. Polygons of the other four species; S. canaliculatus, S. sutor, S. rivulatus and S. argenteus overlapped in the negative part of 2nd PC, suggesting close similarity in their body morphometry. Mann-Whitney U-test confirmed significant vi difference between specimens of S. stellatus and S. luridus (p<0.05) for 7 morphometric characters. The differences were observed between characters of S. luridus and S. argenteus, while the least differences in ED and GAspL were between S. canaliculatus and S. sutor. PCA for S. rivulatus specimen from Msambweni (south) and Malindi (north) coast clear separation of polygons with Malindi specimens falling on the negative part of 1st PC and Msambweni specimens in the positive part. Subsequent character analysis of S. rivulatus from Msambweni and Malindi, confirmed significant difference in ED and GAspL (p ≤ 0.05). Therefore, there is need for further research on taxonomy of S. rivulatus including analysis of molecular genetic variation to confirm whether Msambweni and Malindi rabbitfishes are separate stocks of the same species or two different species.