Effect of branchial parasites on the efficiency of the gills of a freshwater catfish, Wallago attu

For the first time, an attempt has been made to quantify the effect of a co pepod parasite (Ergasilus bengalensis) on the respiratory efficiency of the gills of a riverine catfish (Wallago attu) using an important parameter - the diffusing capacity. In addition., scanning electron microscopy has been used to demonstrate the effect of a monogeneid fluke on the gill lamellae of this catfish. The anchorage of E. bengalensis towards the leading edge o f the interlamellar channels (pores) will affect laminar flow of water thro ugh the gill sieve. About 35% of the water flow (1.23 x 10(-3) cm(3)/s) and lamellar area (15.41 mm(2)) of an infected gill filament (4.46 mm) is affe cted by the copepod parasite (1.59 mm). Other effects of the monogeneid flu kes on the catfish included fusion of the tips of gill filaments and distor tion of lamellar epithelium. Parasite-induced changes in the branchial orga nization are discussed in relation to oxygen uptake efficiency of the gills of the catfish.