Aspects of the biology of Cryptocaryon irritans, and hyposalinity as a control measure in cultured gilthead sea bream Sparus aurata

The life cycle and halotolerance of Cryptocaryon im-tans were studied. Trophonts completed their growth phase on the host in 3 to 7 d. The reproductive process of the tomonts yielded tomites as early as 3 and as late as 28 d. Tomite life span was 24 to 48 h. Trophonts embedded in the fish skin withstood 18 h exposure of the host to fresh water. Tomonts withstood salinities ranging from 20 to 70 %O for 48 h without losing viability. Tomites were seen emerging only from tomonts kept in constant salinities ranging from 25 to 50 %o. All tomonts degenerated when immersed in 0 to 10 %O for 3 h. Eradication of the parasite based on these findings was achieved. Four consecutive treatments of 3 h each in 10 %O salinity 3 d apart destroyed all tomonts before tomites could excyst and were well tolerated by the fish. C. imitans life cycle was similarly interrupted by 4 consecutive transfers of fish into clean tanks at 3 d intervals. A certain degree of resistance to C. irritans invasion was observed in fish that had survived several infections.