Effects of including cationic proteins from cod milt in the feed to Atlantic cod ( Gadus morhua) fry during a challenge trial with Vibrio anguillarum

Abstract

This work was carried out to investigate if oral administration of cationic cod milt proteins to cod fry could improve disease resistance during a challenge trial with Vibrio anguillarum. Atlantic cod fry (5 g) were given a commercial feed supplemented with 0.1% cationic proteins extracted from cod milt. The pre-challenge feeding period lasted 21 days, after which the fish were challenged for 1 h by bath exposure to V. anguillarum (5×10 6 cfu ml −1). Mortality was recorded during four weeks after challenge. From the 12th day after infection and throughout the trial period, significant ( p<0.05) reduced cumulative mortality was registered in fish given the feed supplemented by cationic cod milt proteins. Fish fed the supplemented diet reached final cumulative mortalities of 59% and 66%, while 74% and 75% mortality were recorded in fish given the control diet. The effect of the cod milt cationic proteins on the growth of V. anguillarum was tested using the broth dilution method. At 0–0.9% (w/v) NaCl, growth was inhibited with MICs in the microgram range. These results suggest that supplementation of cod milt cationic proteins to the feed of juvenile fish improves their resistance to this bacterial infection.