Laying, development and hatching of eggs of the fish ectoparasite Argulus japonicus (Crustacea: Branchiura)

Egg laying of the fish-louse Argulus japonicus was observed and examined experimentally. The effect of temperature on development time and hatching yielded an inverse exponential function. Hatching started after 61–10 days in a temperature span of 15–35 °C. Eggs are laid in strings on hard substrata and covered by a gelatinous material. Females lay between 1–9 strings, 5–226 eggs per string, arranged in 1–6 rows. Four embryonic developmental stages were recognized and the mean hatching efficiency was 50% in the optimal temperature range of 20–30 °C. Hatching efficiency was not related to either the number of eggs in a string or the total number of eggs laid by any particular female. Argulus japonicus displays continuous egg-laying activity with a possibility of an overwintering mechanism which suggests a seasonality of a sort.