New Data on the Early Development of Hysterothylacium aduncum (Nematoda, Anisakidae)

Abstract

This note reports on incidental observations of the early development of the third-stage larvae of Hysterothylacium aduncum from gadid fishes. Gravid H. aduncum females were collected from Pollachius virens, Pollachius pollachius. Gadus morhua, and Molva molva in Norwegian waters. The eggs were incubated at 20 per thousand salinity and 5 C. Spontaneous hatching of third-stage larvae was observed 10-25 days after egg deposition. These larvae were long lived and could infect Acartia tonsa copepods, the infections being maintained for up to 34 days. The morphology of the third-stage larvae in the copepods and some traits of the life cycle were similar to those reported in previous studies. However, our results disagree with evidence suggesting that H. aduncum eggs rarely hatch, and hatched larvae have lower survival and a poorer ability to infect the first intermediate host than unhatched ones. It is difficult to account for these discrepancies because information on the early development of Hysterothylacium species is incomplete. However, we tentatively suggest that differences in the early development of H. aduncum may indicate the existence of at least 2 different taxonomic entities in the North Atlantic, which is consistent with previous evidence based on morphological traits.

In vitro development of the fish parasite Hysterothylacium aduncum from the third larval stage recovered from a host to the third larval stage hatched from the egg

“…For eggs from Week 3, these percentages were lower than 0.1%. The larvae started to hatch 23 d after deposition, a time lapse higher than the 10 d previously reported by Yoshinaga et al (1987) and Balbuena et al (1998), although these authors indicated a range of 10 to 22 or 10 to 25 d, respectively. As with the eggs, the hatched larvae also had negative buoyancy in the saline solution used, and tended to be deposited on the bottom of the culture flasks.…”

“…1987, Køie 1993, Balbuena et al 1998, González 1998) may be due to the occurrence of subspecies of Hysterothylacium aduncum (Hartwich 1975, Petter & Cabaret 1995. It could also be due to the occurrence of sibling species of H. aduncum, suggested by Martín-Sánchez et al (1998), as occurs in other anisakids.…”

“…Hatched, ensheathed larvae lived for over 3 to 4 mo at 13°C, but without apparent development. Other authors reported larval survival at 5°C for over 5 mo (Balbuena et al 1998), or for 1 wk at 20°C (Køie 1993), after hatching and remaining ensheathed.…”

“…While working on parasites from large gadids (Balbuena et al 1998) and salmonids (González 1998) a general hatching of developed eggs has been reported. However, the research of Køie (1993), working on worms from eelpout (possibly Hysterothylacium auctum), Yoshinaga et al (1987), working on parasites from freshwater Japanese smelt, which experimentally developed in rainbow trout, and the present study have always shown the rate of hatching larvae to be lower than 33% in seawater and several saline solutions.…”

“…Hatched, ensheathed larvae lived for over 3 to 4 mo at 13°C, but without apparent development. Other authors reported larval survival at 5°C for over 5 mo (Balbuena et al 1998), or for 1 wk at 20°C (Køie 1993), after hatching and remaining ensheathed.The differences among some data obtained in this study and those obtained by other authors (Yoshinaga 44 (Hartwich 1975, Petter & Cabaret 1995. It could also be due to the occurrence of sibling species of H. aduncum, suggested by Martín-Sánchez et al (1998), as occurs in other anisakids.…”