6533b873fe1ef96bd12d5f96

RESEARCH PRODUCT

Oncomiracidial development, survival and swimming behaviour of the monogenean Sparicotyle chrysophrii (Van Beneden and Hesse, 1863)

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Abstract Oncomiracidial development of Sparicotyle chrysophrii , a monogenean parasite of Sparus aurata , was analysed using 450 eggs. Parasite morphological changes in time, data on hatching success, as well as oncomiracidial survival and swimming behaviour were recorded. Eggs were maintained at 20 °C and exposed to LD 12:12. They were observed under the stereomicroscope every 8 h until they hatched. Thereafter, 155 oncomiracidia were isolated in separate wells and observed every 2 h until their death. Most of the hatchings occurred in a short period of time (approximately 24 h). Hatching success was 87% and the hatching period ranged from 5 to 10 days after deposition, with most of the hatchings occurring during darkness (> 75%). Oncomiracidial survival time ranged from 2 to 52 h, although only 10% of the oncomiracidia lived more than 24 h. No significant Spearman's correlation was found between incubation and oncomiracidial survival times. Survival times of the oncomiracidia emerging during darkness period were significantly higher than survival times of those emerging during light. Seven oncomiracidial behaviour patterns were recorded: vertical swimming (fast/slow), horizontal swimming close to the bottom (fast/slow), continuous whirling, alive without ciliary movement and dead. A highly significant correlation was found between survival and swimming times (r = 0.911, p-value = 0.000). The mean swimming speed of oncomiracidia was 3.97 mm/s (n = 10). The complete life cycle of S. chrysophrii (from egg to egg) at 20 °C lasts approximately 50 days: 5–10 days of incubation, 2–3 days of oncomiracidial survival time and 36 days of worm maturation. Treatment involving two applications, first for adults and juveniles and later (after 12 to 15 days) for larvae, would allow long periods without monogenean infection.