Pathology and reproductive health of queen conch (Lobatus gigas) in St. Kitts

Abstract

Queen conch, Lobatus gigas, are one of the largest commercial fisheries in the Caribbean and are severely depleted due to overharvesting. Dwindling and fragmented populations are at high risk to stochastic events such as disease epidemics; however, there is a paucity of literature regarding queen conch disease. A histopathological survey was conducted to assess the disease status of St. Kitts' queen conch populations, and contribute to the little information known about L. gigas pathology. Using a standard dissection and sampling protocol, pathology status was assessed in 61 L. gigas sampled opportunistically from fishermen in St. Kitts from October 2015 to November 2016. Pathology was observed in 13.1% (8/61) of the study population, mostly comprising internal parasitism (n = 5), especially encysted metazoan parasites (likely digenean metacercaria), observed in the gill, mantle, digestive gland and large intestine. Parasitism appeared incidental, having little impact on the host's health and minimal host response to the infection. Additionally, aspects of L. gigas reproductive health were analyzed: reproductive season in St. Kitts was confirmed from May to September; lip thickness is suggested as a better regulation measure for protecting juvenile populations compared to shell length; and variation in gonad color is found to be an unreliable predictor of reproductive activity. We conclude that disease appears to be uncommon in fisherman-caught L. gigas from St. Kitts. Pathologies observed elsewhere, including imposex and apicomplexan infection of the digestive gland, could not be substantiated in the study population. The cryptic nature of sick gastropods, as well as high predation rate and selection pressure for diseased queen conch may yield underrepresentation of pathology in such surveys. Future disease surveys could benefit from targeting stunted individuals, those showing unusual behavior, or those grown in an aquaculture environment.

Keywords: Conch; Disease; Histology; Parasitology; Pathology; Reproduction.