Micropogonias furnieri in Lagoa dos Patos: a study of the relationship between parasitism, fish welfare and aquaculture
Author: Ana Luiza Velloso (Currículo Lattes)
Supervisor: Dr Joaber Pereira Júnior
The croaker, Micropogonias furnieri, represents one of the most important fishing resources in the Southwest Atlantic Ocean and has potential for aquaculture, like other Sciaenidae cultivated in other parts of the world. A considerable amount of information about its biology is available and several studies have been developed on parasites in M. furnieri off the coast of the Brazilian states of Rio de Janeiro, Rio Grande do Sul, São Paulo, Uruguay and Argentina. Thus, croaker can be an appropriate biological model for studying the interactions between parasitism, fish welfare and aquaculture. The objective of this study was to characterize the influence of parasitism by metazoans on corvine in the Lagoa dos Patos estuary,using correlations between the parasitological indices of Prevalence (P) and Intensity of Infection / Infestation (II) with somatic indices: Gonado-Somatic Index (IGS), Hepato-Somatic Index (IHS) and Relative Condition Factor (Kn), which are indicators of well-being. For this, samples from two environments were studied: pre-limnic (farthest from the Atlantic coast) and estuarine (closest to the coast), as differences in these environments could be reflected in the parasitic fauna. In addition, the relationship between parasitism, fish welfare and aquaculture was discussed. The function-based definition of animal welfare was used, where welfare means that the animal is in good health, with its biological systems functioning properly and not being forced to respond beyond its capacity. In the first chapter,the influence of ectoparasitism on M. furnieri's well-being is characterized. For this, 181 specimens of croaker were necropsied and the parasites found were: Gauchergasilus euripedesi (Copepoda), Myzobdella uruguayensis (Hirudinea), Neomacrovalvitrema argentinensis and Neopterinotrematoides avaginata (both Monogenoidea). The relationship between parasitic abundance and the somatic indexes of the host was verified, but no significant correlation was determined, suggesting the host's tolerance to parasitosis in the values found. In addition, the comparison of samples in the pre-limnic and estuarine environments showed differences in the diversity and intensity of parasitic species found, suggesting a preference of the parasites for different salinities. In the second chapter,the relationship between endoparasitism and the well-being of the croaker is established. As with ectoparasites, there was no significant correlation, suggesting a balance between hosts and parasites, which is expected for fish in a natural environment. Among the endoparasites found are Aspidogastridae and Nematoda (mainly Anisakidae). The variation in the intensity of Aspidogastridae by sampled location may be related to the viability of the life cycle of these parasites. The direct pathogenic effect of the presence of Nematoda is much less important than its role as causative agents of zoonoses. In addition, consumer attitudes towards their presence, especially due to the aesthetics of the parasitized product, can have a major impact on the market value of fish, highlighting the need for monitoring.In the third chapter, a review is presented on how the effects of parasitism on fish can be related to fish welfare and aquaculture, using the recent information available on the topic. Finally, a set of considerations is presented that, in addition to establishing relationships between the three chapters, suggests some recommendations. The impact of salinity on host-parasite interactions is a potential regulator of the parasite's survival and transmission processes. This is important information for the cultivation of M. furnieri, as it suggests that the control of these parasites can be accomplished by regulating the levels of salinity. It must be considered that diseases are part of nature and, when understood in this way, it becomes easier to deal with their occurrence.Prophylaxis and surveillance should be the guiding principles in modern aquaculture; treatment should be used only when strictly necessary, avoiding the introduction of drugs into the environment. Thus, the parasites must be considered as part of this process, monitoring them, but without the intention of excluding them. Thus, it can be said that it is possible to sustain the interaction between parasites, well-being and aquaculture.