Seasonal occurrence, sex ratio and site preference ofArgulus coregoniThorell (Crustacea: Branchiura) parasitic on cultured freshwater salmonids in Japan

Abstract

SUMMARYAnalysis of the seasonal occurrence of Argulus coregoni on Oncorhynchus masou and Salmo gairdneri indicates that the parasites overwinter as eggs and that there are 1 or 2 generations/year. Larvae which hatch from the overwintered eggs are abundant from May through July. Individuals hatched in May and June attain maturity and lay eggs in August. Larvae of the second generation are abundant in September, and they lay eggs in October–November which overwinter. Hatched larvae from overwintered eggs may mature in July and deposit overwintering eggs in September. The sex ratio of A. coregoni is about 1:1. A. coregoni shows an age-specific site preference on O. masou. Small parasites occur on almost all parts of the skin and fins, with slightly heavier concentrations on and around the pectoral and pelvic fins. Large parasites are found mainly on the skin around these fins.

Diel variation in egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea: Branchiura)

“…based on removal of deposited eggs have yielded some success (Bauer 1959, Shimura 1983, Gault et al 2002. Floating wooden boards have been used in Eastern Europe as a substrate for A. foliaceus egg-laying (Bauer 1959), whilst transparent acrylic plates have been adopted in Japan to facilitate removal of A. coregoni egg clutches from fish-rearing ponds (Shimura 1983). Efficient control, however, relies on our understanding of both seasonal and diel egg-laying patterns of these species (Harrison et al 2006).…”

Praziquantel, levamisol e difubenzuron no controle de Dolops carvalhoi (Crustacea: Branchiura) e Anacanthorus penilabiatus (Monogenea: Dactylogyridae) em Piaractus mesopotamicus Holmberg, 1887 (Osteichthyes: Characidae)

“…Diariamente foi determinada a temperatura, pH e oxigênio dissolvido e, a cada 3 dias, a concentração de amônia. Todas as características hídricas permaneceram dentro de parâmetros adequados para os peixes (SIPAÚBA-TAVARES, 1995). Em cada colheita, os peixes foram anestesiados em solução aquosa de benzocaína 1:10.000 (NOGA, 1996), medidos e pesados.…”

“…e Dolops sp., parasitam a superfície corporal, nadadeiras e brânquias de várias espécies de peixes silvestres e de cativeiro (EIRAS, 1994;PAVANELLI et al, 2002). Como são histófa-gos, a penetração do seu aparelho bucal causa dano mecânico ao hospedeiro e a injeção de enzimas tóxicas determina inflamação local (SHIMURA, 1983). A agressão do Dolops sp.…”

“…Nas brânquias há hipertrofia com hiperplasia do epitélio de revestimento e de células mucóides, além de focos necróticos, que prejudicam as trocas gasosas e iônicas. Os parasitos atuam como vetores de bacterioses e viroses de importância (SHIMURA, 1983). Os Dactylogyridae têm forma alongada, são monoxê-micos, com exceção do Diplozoon sp., favorecendo as grandes infestações.…”

Aggregation ofArgulus coregoni(Crustacea: Branchiura) on rainbow trout (Oncorhynchus mykiss): a consequence of host susceptibility or exposure?

“…Variations in exposure to infective stages of fish lice are expected to exist in nature, because A. coregoni egg clutches were shown to be located in an aggregated manner (Hakalahti et al 2004). Spatial heterogeneity in the existence of infective stages coupled with seasonal dynamics in their emergence is likely to cause variations of exposure especially when we consider that the hosts of A. coregoni are highly mobile salmonids (Shimura, 1983 ;Hakalahti & Valtonen, 2003). Hosts that happen to be near emergence sites of A. coregoni during the most intensive spring hatching period are likely to be under highest exposure pressure.…”