Trophic ecology and isotopic and physiological biomarkers of wild fish species associated with cage fish farms

Author(s)

Bruna Caroline Kotz Kliemann

• Document type: Doctoral Thesis
• Press: Botucatu. 2023-02-27.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Botucatu
• Defense date: 2023-02-17
• Advisor: Igor Paiva Ramos; Rosilene Luciana Delariva

Abstract

The production of freshwater cage fish farms plays an important role in the national and world economy. In these systems, the breeding is intensive, with fish confined at high densities in empty, floating cages, fed with intensive pelleted feed intake. The release of organic matter, composed of uneaten pelleted feed and excreta from farmed fish, is one of the main concerns related to cages fish and causes changes in the local ichthyofauna diet. In this sense, changes in diet can alter the structure of local communities due to interference at different trophic levels. Effects of cage fish farms on fish diet can also result in physiological changes in organs such as liver and gonads in response to high concentrations of protein and energy in the pelleted feed. Thus, the general objective of the present study was to evaluate the influences of cage fish farms on the introduced species Geophagus sveni and Plagioscion squamosissimus by means of diet and assimilation (stable isotopes) of food resources, as well as the quantification of the energetic substrates protein, lipid and total glycogen. For this purpose, fish were collected from sites with (TR) and without (CT) cage fish farms in a Neotropical reservoir. Through stomach contents, pelleted feed consumption was observed in sites with the presence of fish farms. Although pelleted feed consumption was not observed in the stomach contents of carnivorous fish and fish at sites without fish farms, stable isotope analysis demonstrated that pelleted feed assimilation occurred. From this, the influences of cage fish farms go beyond pelleted feed consumption or increases in the abundance of fish and other organisms around the cages, indicating influences at various trophic levels and at sites where no fish farms are in operation. Furthermore, analyses of protein, lipid and glycogen concentrations in liver, gonadal and muscle tissues differed according to the high percentages of protein in the pelleted feed. Higher hepatosomatic index values for fish at the sites where higher percentages of pelleted feed assimilation occurred (CT1, TR1, TR2 and TR3) indicated higher energy reserves in the liver, corroborating the energy potential of the pelleted feed. Thus, the approaches evaluated here were effective in demonstrating the influences of cage fish farms by reporting that both species assimilated pelleted feed lost to the aquatic environment. Furthermore, the results showed that this assimilation promoted changes in the concentrations of energetic substrates, raising questions about the consequences of these physiological changes for the reproduction of these species. Could these high concentrations of protein and energy favor the reproduction and growth of these species, thus increasing the fish stock? Could it favor the maintenance of these populations of non-native species? What is the effect on native species? Future studies covering the community over a longer time series and with native species are needed to answer these questions. The results observed here can also provide information to fish farmers about the consequences of the loss of organic matter to the aquatic environment, as a parameter for mitigating measures that can reduce such loss. (AU)

• FAPESP's process: 18/01117-2 - Trophic ecology and physiological biomarkers of two species of fish belonging to different trophic guilds (omnivorous and carnivorous) associated to cage fish farms
• Grantee: Bruna Caroline Kotz Kliemann
• Support Opportunities: Scholarships in Brazil - Doctorate