Fish-food interaction network around cage fish farming in a neotropical reservoir

Heleno Brandão,Daniel Rodrigues Blanco,Igor Paiva Ramos,Edmir Daniel Carvalho,André Batista Nobile,Jamile Queiroz De Sousa,Denise Lange

doi:10.1590/s2179-975x10919

Abstract

Abstract: Aim Investigating whether wild fish accept residual ration from cage fish farming to the point of changing their diet and the fish-food interaction network. Methods The diet of fish species, Astyanax lacustris, Iheringichthys labrosus, Leporinus amblyrhynchus, Schizodon nasutus and Steindachnerina insculpta, bred in Chavantes Reservoir, Upper Paraná basin, was evaluated. Samples were collected on a monthly basis - from March 2008 to February 2009 - around the cage fish farming (NC) and in a reference site (RS) free from the influence of the fish farming activity. Results were analyzed through graphs and metrics of complex network analysis, and Permutational analysis of variance. Results The total number of 641 individuals belonging to all five fish species were collected, 292 in NC and 349 in RS. The total amount of food items consumed by them comprised 24 items in NC and 22 items in RS. The fish-food interaction network has shown nested pattern in the two evaluated areas, which evidenced the generalist structure of this interaction. Connectance values and mean degree of interaction networks were low. Detritus was the most representative item consumed in both sampling sites. Three of the five evaluated species (A. lacustris, S. nasutus and I. labrosus) had residual ration in their diet. Residual ration was the fourth most consumed item in NC. It was also the most representative food item for A. lacustris and S. nasutus. Conclusions Results have shown that cage fish farming activity can influence trophic interactions in aquatic systems, as well as evidenced the ability of S. nasutus, L. labrosus and A. lacustris to take advantage of new food items in their environment.

Highlights

Aquaculture is one of most relevant zootechnical activities in constant development worldwide
The low mean degree value reflected the connectance of food item‐fish interaction networks, which only resulted in 9.16% possible interactions established in reference site (RS) and in 12.03%, in NC
These results are indicative that the investigated fish species were generalists, since they consumed different food items

Summary

Introduction

Aquaculture is one of most relevant zootechnical activities in constant development worldwide. Negative effects caused by cage fish farming systems have already been investigated in marine (Bartozek et al, 2014; Hedberg et al, 2015; Price et al, 2015; Tomassetti et al, 2016; Barrett et al, 2019) and freshwater ecosystems (Hakanson, 2005; Carvalho et al, 2012; Demétrio et al, 2012; Ramos et al, 2013; Kliemann et al, 2018; Nobile et al, 2018, 2020) in several regions all around the globe This activity leads to changes in natural environments, wild animal populations and landscape. Researchers have been trying to get to consensus between sustainable fish production and damage to aquatic ecosystems, based on procedures such as delimiting suitable locations for aquaculture sites, using mathematical modeling to determine the carrying capacity of the environment (David et al, 2015) and, more recently, Integrated Multitrophic Aquaculture - IMTA (see Ning et al, 2016; Montalto et al, 2017)

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