Water quality tolerance and gill morphohistology of pure and reciprocal crosses of Pangasianodon hypophthalmus and Clarias gariepinus

Abstract

Tolerance to degrading water qualities in relation to the gill morphohistology was investigated in pure and reciprocal crosses of two important catfishes. Progenies of Clarias gariepinus (CG), Pangasianodon hypophthalmus (PH), Pangapinus (♀PH×♂CG) and the two observed morphotypes (Clarias-like and Panga-like) of Clariothalmus (♀CG×♂PH) were obtained from the same breeding history. These fishes were cultured in a static system without aeration and at high stocking density for a maximum period of two weeks. Mortality and water quality were monitored daily. Total mortality was observed 24 h post exposure (1DPE) in the Panga-like Clariothalmus, while the Pangapinus and pure P. hypophthalmus did not survive beyond the third day (3DPE). However, total mortality was not recorded in the Pure C. gariepinus and Clarias-like Clariothalmus even after 14DPE. Morphohistology of the gills of the latter fishes showed the presence of an accessory breeding organ in the form of branched bulbous dendritic-like structures and less occurrence/severity of many histopathological conditions observed during the challenge experiment. However, this was not the case with the other fish groups. It was concluded that the architecture and the level of susceptibility of the gill influenced the tolerance ability of the different fishes to poor water quality.