The Structural and Functional Morphology of the Hard Parts of Brycinus nurse (Pisces: Cypriniformes, Characidae), From Asa Reservoir, Ilorin, Nigeria

摘要

The structural and functional anatomy of the scale, operculum and otolith of 980 specimens of Brycinus nurse Paugy, from Asa reservoir was investigated within the period November 1991 to October 1993. The physicochemical parameters of the reservoir were also investigated within the same period. The scale, opercula bones and otoliths all showed growth markings. However the growth marks on the opercula bones and otoliths could not be interpreted and were not reliable in estimating the age of the species. 91.94% of the opercula bones examined had no growth marks and the phenomenon of false marks was a common occurrence in a great majority. 7.96% had only 1 growth mark and 0.10% had 2 complete growth marks. One growth mark was laid down annually on the operculum. Both the cyclical and daily growth marks were recorded on the otolith; however the daily growth marks showed a marked disparity when compared with the days of the observed age of the fish. A maximum of 4 growth marks were recorded on the scale of a female specimen of 15.10 cm TL This growth marks were produced by cutting over. Two growth marks are laid down annually on the scales. The first growth mark was laid down between January and February coinciding with a drop in temperature while the second growth mark was formed between July and August coinciding with the period of flooding in the lake. The growth marks on the scale, were clear, reliable and easy to interpret making the scale of B. nurse the most popular and reliable means of estimating the age and calculating the growth of the fish.