The effect of dietary soybean meal and soy protein concentrate on the intestinal mucus layer and development of subacute enteritis in Yellowtail Kingfish (Seriola lalandi) at suboptimal water temperature

Solvent-extracted soybean meal (SESBM) has been reported to cause subacute enteritis in certain fish species. Two 34-day experiments investigated the effects of SESBM and soy protein concentrate (SPC) on the intestinal mucus layer and development of subacute enteritis in the hindgut of yellowtail kingfish (Seriola lalandi) at 22 and 18 degrees C. Fish were fed increasing levels of SESBM (Exp. 1: 0 g kg(-1), 100 g kg(-1), 200 g kg(-1), 300 g kg(-1)) and SPC (Exp. 2: 0 g kg(-1), 200 g kg(-1), 300 g kg(-1), 400 g kg(-1)). No visual signs of inflammation in the hindgut were observed in either experiment. However, increasing dietary SESBM significantly reduced mucus layer thickness. Neutral and acidic goblet cell mucin composition increased at 18 and 22 degrees C, respectively. A significant positive linear relationship was evident between goblet cell number and SESBM inclusion at 18 degrees C. SPC inclusion and water temperature had no significant effect on mucus layer thickness or mucin composition. However, at 18 degrees C, goblet cell numbers decreased with SPC inclusion. Results suggest the early stages of subacute enteritis may have been manifesting in SESBM fed fish. In the long term, mucus layer alterations associated with feeding SESBM may compromise fish health. Longer-term studies should investigate the effects of feeding SESBM to yellowtail kingfish, particularly at suboptimal water temperatures.