EFFECTS OF WATER TEMPERATURE ON MUCOUS CELL DISTRIBUTION IN CHANNEL CATFISH EPIDERMIS - A FACTOR IN WINTER SAPROLEGNIASIS

The influence of an acute drop in water temperature on channel catfish (Ictalurus punctatus) mucous cell distribution in the epidermis was e xamined. Channel catfish were subjected to a water temperature drop fr om 22 to 10 degrees C in 24 h and sampled for histological examination of the epidermis at regular intervals. Three days after the drop in w ater temperature, there was a marked decrease in the number of mucous cells in the outermost (superficial) portion of the epidermis. The num ber of mucous cells returned to normal levels after fish were maintain ed at 10 degrees C for 6 days. If catfish were subjected to the temper ature drop and also challenged with Saprolegnia, mucous cells in the s uperficial epidermis did not recover to normal levels but continued to decline from day 3 until the fish subsequently died from saprolegnias is. These results may explain the dry skin appearance characteristic o f catfish exhibiting winter saprolegniasis. Furthermore, since Saprole gnia cysts are normally shed in sloughed mucus, low temperature-induce d mucus loss may explain how Sapralegnia cysts attach and infect catfi sh skin to result in disease. These results also reinforce the notion that an intact external mucus layer is the first line of defence again st infectious disease in fish. (C) 1998 Academic Press Limited.