Fabrício Martins Dutra

Invasion risks by non-native freshwater fishes due to aquaculture activity in a Neotropical stream

This study investigated the potential of aquaculture to spread non-native species associated with a high risk of invasiveness. We identified the biogeographic origin of produced fish species in the micro-watershed of the São Camilo stream, Brazil, the occurrence of non-native species in the São Camilo stream and the potential risk of biological invasions. Fish farmers were interviewed to obtain information about the species produced, and samples with electrofishing equipment were taken in the stream to detect the occurrence of non-native species. The Fish Invasiveness Screening Kit (FISK) protocol was applied to classify non-native species according to their invasive potential. We identified 59 fish farms and 19 produced fish species, including 13 non-native species. The non-native species Oreochromis niloticus represented 93% of production and was the second most abundant species in the stream. Eleven species were classified with a high invasive potential and two with a medium potential. The results showed the prevalence of non-native species use in aquaculture, with species escapes with a high invasive potential. Thus, the non-native species produced in aquaculture represent an important vector of introductions and risk to biodiversity conservation. It is vital to establish biosafety norms, to enable aquaculture to develop in a sustainable way.

Histological alterations in gills of Macrobrachium amazonicum juveniles exposed to ammonia and nitrite

Aquaculture has shown great growth in the last decades. Due to the restrictions on water use, production systems are becoming increasingly more intensive, raising concerns about the production water quality. Macrobrachium amazonicum is among the freshwater prawn species with favorable characteristics for production and possibility of intensification. Nitrogen compounds such as ammonia and nitrite affect the health of aquatic organisms since they quickly reach toxic concentrations. These compounds can also cause damage to the gill structure, leading to hypoxia in tissues, affecting acid-base balance, osmoregulation (salt absorption) and ammonia excretion, decreasing the immune capacity of the animal and, in extreme cases, cause death. The aim of this study was to assess histological changes in the gills of Macrobrachium amazonicum juveniles subjected to different concentrations of total ammonia and nitrite. The prawns were subjected to different concentrations of those compounds and their gills were removed and preserved for histological analysis. The gills were assessed for changes according to the Organ Index (Iorg) and, for each change, an importance factor (w) was attributed according to the degree of reversibility and applied according to the degree of extension or frequency of the damage. The damage to the gills in the treatments with 100% mortality, both for ammonia and nitrite, corresponded to the high occurrence of progressive, regressive, circulatory, and inflammation damages. The other treatments (which caused less mortality) had mainly inflammation and regressive damages, whose occurrence increased according to the increase in ammonia and nitrite concentration. The histological analysis confirmed that the higher the total ammonia and nitrite concentrations, the larger the damages caused to the gill structure and that lower nitrite concentrations caused similar damages to those caused by higher total ammonia concentrations, which reflects the lower capacity M. amazonicum has to tolerate nitrite.