Zeuxapta Seriolae Research Articles

Efficacy of Aqui-S, formalin and praziquantel against the monogeneans, Benedenia seriolae and Zeuxapta seriolae, infecting yellowtail kingfish Seriola lalandi lalandi in New Zealand

This study assessed the efficacy of bath administrations of Aqui-S, formalin and praziquantel against adults and eggs of Benedenia seriolae and Zeuxapta seriolae, two monogenean ectoparasites of kingfish ( Seriola lalandi lalandi). Our results showed that 2.5 ppm praziquantel administered for either 24 or 48 h was the most effective treatment for removing B. seriolae (>99%). However, B. seriolae treated with praziquantel for 24 h deposited viable eggs. Formalin at 250 and 400 ppm for 1 h followed by a 5 min freshwater dip was less effective for removing B. seriolae (ca. 80%), but both treatments inhibited the production of eggs by treated parasites. However, a large proportion of B. seriolae eggs exposed to either formalin treatment remained viable. Praziquantel (2.5 ppm for either 24 or 48 h) and formalin (400 ppm for 1 h+5 min f/w dip) were the most effective treatments for removing Z. seriolae from the gills of kingfish (>99%) but the parasites thus removed continued to deposit viable eggs. Exposure to the anaesthetic Aqui-S did not significantly increase numbers of B. seriolae or Z. seriolae removed from the host above those of the control, but it was ineffective in preventing the production of eggs by treated parasites, and did not reduce egg viability. Eggs of B. seriolae were not prevented from hatching unless exposed to air for a period greater than 3 h, and Z. seriolae eggs were only prevented from hatching if exposed to air for periods greater than 5 h prior to the development of eyespots. These results indicate that both primary and secondary treatments will be required to successfully control B. seriolae and Z. seriolae infections in captive kingfish.

Effects of the gill parasite Zeuxapta seriolae (Monogenea: Heteraxinidae) on the amberjack Seriola dumerili Risso (Teleostei: Carangidae)

Zeuxapta seriolae (Monogenea: Heteraxinidae) infection was associated with important mortalities of amberjacks ( Seriola dumerili) reared in tanks in the experimental facilities of the Spanish Institute of Oceanography (Western Mediterranean) during the period 1998–2000. Fish infested by this parasite presented characteristics similar to those described for Seriola quinqueradiata parasitized by Heteraxine heterocerca in Japan. All dead amberjacks had high parasite abundance (mean abundance±S.D.=686.7±125.4) and egg strings entangled in gills. The parasitological analysis of 17 live amberjacks collected from the infested tanks showed that 41.2% of fish harboured Z. seriolae with intensities ranging between 5 and 731 parasites per fish. No apparent relationship was observed between the abundance of the parasite and the condition factor ( r S=0.175, n=17, p>0.5). However, the haematocrit values were significantly lower in the fish infested with monogeneans. The relationship between parasite abundance and haematocrit values was negative and statistically significant ( r S=−0.625, n=17, p<0.01). The light and scanning electron microscope studies of affected gills revealed that the parasites attached to the host grasping one or two lamellae with each clamp of the haptor, which led to lamellar synechiae, lamellar clubbing and disruption of epithelial and vascular structures. A mild to moderate epitheliocystis infection was also detected in gills. Combined effects of gill damage and parasite blood feeding could be related to the anaemia and, finally, the death of the fish.

Metazoan parasites of yellowtail kingfish, Seriola lalandi lalandi, in New Zealand: Prevalence, intensity, and site preference

The prevalence and intensity of metazoan ectoparasites on the skin and gills of kingfish, Seriola lalandi lalandi (Carangidae), collected from White Island (n = 32), Ranfurly Banks (n = 7), and Three Kings Islands (n = 7), is reported. Kingfish were host to two monogenean and four copepod ectoparasite species, Benedenia seriolae, Zeuxapta seriolae, Caligus lalandei, Caligus aesopus, Neobrachiella spp., and Lernanthropus spp., respectively. B. seriolae and C. lalandei infect the skin, whereas the remaining parasites were located on the gills. All parasites exhibited considerable variability in the prevalence and intensity of infection. A few kingfish were completely devoid of C. aesopus, Neobrachiella spp., and/or Lernanthropus spp., whereas others were infected by moderate numbers of these species. However, all kingfish were infected by B. seriolae and Z. seriolae. Therefore, it appears that acclimation of wild kingfish from the east coast of New Zealand's North Island into captivity will lead to the transfer of both B. seriolae and Z. seriolae, and that effective quarantine measures will be required to avoid introducing these parasites into broodstock systems. The site preferences of B. seriolae, Z. seriolae, and C. aesopus were also investigated. B. seriolae exhibited a preference for attachment on the lateral surfaces of the skin behind the dorsal fin, but forward of the anal fin. Z. seriolae displayed a preference for attachment on gill arches 2 and 3, particularly in gill filaments located in the upper regions of the buccal cavity. C. aesopus most commonly occurred on the gill arch.

Ultrastructure of the Pharynx and Some Parenchyma Cells of Zeuxapta-Seriolae and Paramicrocotyloides-Reticularis (Monogenea, Polyopisthocotylea, Microcotylidae)

The ultrastructure of the pharynx of Zeuxapta seriolae and Paramicrocotyloides reticularis (Monogenea : Microcotylidae) is described. The pharynx of both species is surrounded by a thick sheath resembling a basal lamina. It contains layers of longitudinal, circular and radial muscles, glandular cells, smaller cells interpreted as connective tissue cells, axons, and loose connective tissue. The cell bodies of the glandular cells are subdivided by deep invaginations of cell membranes; the cytoplasm is rich in granular endoplasmic reticulum and golgi complexes. The pharyngeal lumen is branched and lined with a layer of cytoplasm which contains numerous surface lamellae, branched 'supportive' lamellae, and vesicles. A body consisting of stacks of tubules, and associated with axons, is interpreted as a proprioceptor. Bacteria were found in the cytoplasm of some parts of the pharynx of Z. seriolae, particularly near the lumen. In Z. seriolae, three types of parenchyma cells near the pharynx were examined. All have deep invaginations of the cell membrane which, at least in some cells, are anchored near the nucleus by means of desmosomes, and which contain processes of adjacent cells.