Neobenedenia pargueraensis n. sp. (Monogenea: Capsalidae) from the red hind, Epinephelus guttatus, and comments about Neobenedenia melleni

Neobenedenia pargueraensis n. sp. from Epinephelus guttatus of Puerto Rico differs from all known species in possessing scoop-shaped accessory sclerites with pointed tips. It is most similar to Neobenedenia melleni and Neobenedenia longiprostata but differs from the former in having a fenestrate ovary and from the latter in that the ducts of the accessory glands are short, terminating just anterior to the vitelline reservoir rather than reaching the caudal end of the body. It differs from both species in having smooth rather than lobate testes. Neobenedenia melleni occurs throughout the tropical and subtropical western North Atlantic including Bermuda. It kills aquarium and aquaculture fishes with massive infestations and is a severe restraint on the culture of tilapia in sea water in the Caribbean.

Diplectanidae (Monogenea) infestations of sea bass, Dicentrarchus labrax (L.), from the Spanish Mediterranean area. Histopathology and population dynamics under culture conditions

In the present study, Diplectanum laubieri was redescribed from material obtained from wild and cultured fish. The population dynamics of D. aequans and D. laubieri under culture conditions was studied. The prevalence and mean intensity (average number of worms per parasitized fish) were 80.64% and 112 for D. aequans and 67.74% and 59.61 for D. laubieri, respectively. Both Diplectanidae exhibited seasonal variations, with maximal infection levels occurring in winter, suggesting continuous parasites recruitment, and infection levels tended to increase with host age. Male hosts were more heavily infested than females. The apparent positive association between D. aequans and D. laubieri was not confirmed statistically. The Diplectanidae showed definite and different patterns of gill distribution. Histopathological gill damage mainly consisted of hyperplasia of the epithelium, fusion of branchial lamellae and the presence of hemorrhagic and inflammatory foci with leucocytic infiltration. The results demonstrated the pathological importance of both Diplectanidae for the cultivation of sea bass.

Proteocephalus ambloplitis and Contracaecum sp. from largemouth bass (Micropterus salmoides) stocked into Boundary Reservoir, Saskatchewan

Nonresident (introduced) largemouth bass (Micropterus salmoides) from Boundary Reservoir, Saskatchewan were examined for helminths. Four species of parasites were found (Diplostomum sp., Proteocephalus ambloplitis, Pomphorhynchus bulbocolli, and Contracaecum sp.). Contracaecum sp. larvae were absent in age-0 and age-1 bass, but prevalence and mean intensity increased with age for bass age-2 or older. Similarly, the prevalence and mean intensity of P. ambloplitis plerocercoids in bass were low until age-2; older bass harbored significantly more plerocercoids. Analysis of stomach contents indicates that this pattern of recruitment for Contracaecum sp. and P. ambloplitis is probably due to increased feeding by largemouth bass on aquatic insects and cannibalism after age-2, respectively. Although Contracaecum sp. may have been established in the reservoir prior to the introduction of bass, we are certain that P. ambloplitis was introduced via stocking with infected fingerlings.

Adaptation of an introduced host to an indigenous parasite

Introduction of striped bass to the west coast from the east coast of the U.S.A. provided the opportunity to study a recent host-parasite association in a marine system. An indigenous species of parasite was known to induce pathological changes in the introduced population. Because the west coast population has been in association with this pathogenic parasite more than 20 generations, we predicted that the host reaction of the west coast population would be less severe compared to that of the naive east coast stock of striped bass. This prediction was tested by conducting reciprocal infection experiments with east and west coast hosts and parasites. The group of west coast striped bass had a lower intensity of infection and exhibited less tissue damage compared to the group of east coast striped bass. We suggest that selection has acted only on the host and is driven by parasite-induced host mortality. This type of 1-sided selection is in contrast to present models of the evolution of host-parasite associations.

Interaction of bass tapeworm, Proteocephalus ambloplitis, and Neoechinorhynchus sp. (Acanthocephala) in largemouth bass, Micropterus salmoides

The number of plerocercoids of the bass tapeworm, Proteocephalus ambloplitis, in wild largemouth bass was negatively correlated (r = -0.94) with the number of Neoechinorhynchus sp. Competitive inhibition between the 2 parasites appeared to exist. Similarly, the numbers of Neoechinorhynchus sp. in wild bass decreased when adult bass tapeworms were present in the intestine. Proteocephalus ambloplitis plerocercoids used to challenge bass vaccinated with either P. ambloplitis adult or Neoechinorhynchus sp. antigens were smaller (P less than 0.05) when recovered than those used to challenge control bass. Based on preliminary results, both antigens might have enabled the bass to limit growth and/or development of the invading bass tapeworm, plerocercoids. Cross-protective immunity may be the reason for this occurrence, in which case, it could offer an explanation for competitive inhibition existing between P. ambloplitis and Neoechinorhynchus sp.