Hatching of the Pacific salmon leech ( Piscicola salmositica) from cocoons exposed to various treatments

Abstract

Cocoons of Piscicola salmositica deposited on rocks (3–4 cm in diameter) by captive leeches were incubated in tanks supplied with continously flowing well water at 8–10°C from November 1984 to February 1985. The percentage of leeches that hatched from cocoons that were treated with either a total residual chlorine (TRC) concentration that decreased from 602 to 94 μg/l during the 24-h exposure period (64% hatched) or a 1 10 dilution of stock iodophore disinfectant (Wescodyne ®) for 10 min (63% hatched) was not statistically different from the percentage that hatched from untreated control cocoons (53% hatched). The percentage of leeches that hatched from cocoons treated with TRC concentration that decreased from 52 to 4 μg/l during the 24-h exposure period (78% hatched) was significantly increased over that of the controls. A statistically significant reduction in the percentage of cocoons that hatched occurred after exposure to air at 20°C and 80% relative humidity for 24 h (23% hatched). No leeches hatched from cocoons subjected to freezing in or out of water at −5°C for 7 days, exposed to air at 16–20°C and 75–84% relative humidity for 7 and 28 days, or exposed to a 1 10 dilution of a 10.8% sodium hypochlorite solution for 10 min. Leeches hatched over a period of about 152 days with peak hatching during October. Despite exposure of cocoons to various treatments and incubation in well water at 8–10°C from the day the cocoons were deposited until the experiment was terminated (29 November 1984–18 February 1986), and incubation in almost total darkness for the last 238 days, the emergence of leeches in the experiment was synchronous with the hatching of “wild” leeches in the field.