Cage culture with tilapia induces alteration in the diet of natural fish populations: the case of Auchenipterus osteomystax

Abstract

Fish rearing in cages installed in reservoirs has developed rapidly in Brazil over the last decade. However, this type of aquaculture induces some changes in the environment because of the high quantity of nutrients released into the surroundings. This study evaluated trophic changes resulting from these nutrient inputs into the diet, feeding activity and nutritional condition of Auchenipterus osteomystax, an insectivore that alternatively feeds on zooplankton. Fish were sampled with gillnets in two tilapia (Oreochromis niloticus) experimental caging aquaculture areas of the Rosana reservoir (Paranapanema River), at different distances from the cages. Samplings were carried out for 90 days (before the cages were installed and 30 and 60 days after installation). Diet analysis was based on 250 stomach contents evaluated with occurrence and volumetric methods, combined into a Feeding Index. The spatial and temporal variations in feeding activity were inferred by the stomach repletion index (stomach weight). The relative condition factor was used to evaluate the individual nutritional condition of the sampled fish. Insects and zooplankton accounted for more than 85% of the diet in any sample. Insects predominated before caging culture started and at the end of the sampling period, whereas zooplankton predominated 30 days after caging began. The repletion index increased at 30 days after caging in both areas when the condition factor was the lowest, with some recovery at the end of this period. The input of nutrients near caging areas caused a short elevation in zooplankton availability, which promoted changes in the diet of this opportunist species, increasing its feeding activity. However, these changes appeared to be unsustainable due to the poor nutritional condition of the individuals.Keywords: eutrophication, reservoir, aquaculture, feeding, condition factor. Cultivo de tilápias em tanques rede induz alterações na dieta de comunidades naturais: o caso de Auchenipterus osteomystaxResumo O cultivo de peixes em tanques rede é uma prática crescente nos últimos anos. Entretanto, este tipo de cultivo pode causar algumas alterações no ambiente, devido à alta quantidade de nutrientes aí liberados. Assim, o objetivo deste trabalho foi avaliar as influências proporcionadas pelo cultivo de tilápias em tanques rede sobre a dieta, a atividade alimentar e a condição nutricional da surumanha Auchenipterus osteomystax, uma espécie insetívora, porém com zooplanctivoria facultativa. Os peixes foram capturados em redes de espera em duas áreas experimentais de cultivo, localizadas em dois braços do reservatório de Rosana, rio Paranapanema -Pr, a diferentes distâncias dos tanques, em intervalos de 30 dias entre as amostragens. Uma captura foi antes do início do cultivo e as demais nos dois meses subsequentes. Para a análise da dieta, foram utilizados 250 estômagos, sendo os seus conteúdos avaliados através dos métodos de ocorrência e volumétrico combinados no Índice Alimentar (IAi%). As variações espaciais e temporais na at...

Fish assemblages in Neotropical reservoirs: Colonization patterns, impacts and management

“…Such impacts are evident in the intensive farming conducted in caging nets installed in Brazilian reservoirs, which has received subsides from the governmental financial agencies related to fish production (Agostinho et al, 2008b;Lima et al, 2012). Although fish farming in cages has not been adequately monitored, preliminary studies already indicate some distortions with regard to proposed objectives, conflicts among users, profitability, introduction of species, and aquaculture as a source of water quality degradation (Agostinho et al, 2007a;Strictar-Pereira et al, 2010;Azevedo-Santos et al, 2011;Pelicice et al, 2014). Given the common occurrence of escapes in aquaculture, the use of non-native species was prohibited in reservoirs where these species were not established.…”

The influence of fish culture in floating net cages on microbial indicators of water quality

“…Special attention must be paid to cyanobacteria blooms, which are symptomatic of eutrophication in productive lakes, since they may produce cyanotoxins (Funari and Testai, 2008;Semyalo et al, 2010) which are toxic to vertebrates and can affect human health through direct contact or consumption of contaminated water, fish or plants. Caging aquaculture may also cause other impacts on aquatic environments, such as the destruction of natural habitats and alterations in the structure and dynamics of local organisms, as well as trophic changes (Agostinho et al, 2008;Strictar-Pereira et al, 2010;Dias et al, 2012).…”

Cage aquaculture in Neotropical waters promotes attraction and aggregation of fish

“…Fish aggregation was observed in the vicinities of the cages from the beginning of tilapia farming, even under small‐scale experimental conditions (total area of the cages was 48 m 2 ). Although fish can be attracted by natural or artificial physical structures in aquatic ecosystems (Gois, Antônio, Gomes, Pelicice, & Agostinho, ; Rilov & Benayahu, ), the increases in species richness indicate that species that were absent at the cage site prior to cultivation were attracted to the experimental area, staying there and even becoming abundant in some cases, as was observed for P. maculatus and M. maculatus , both species that stand out for the consumption of the feed surplus that was released in the environment (Carvalho, Vidotto‐Magnoni, & Ramos, ), and A. osteomystax , probably attracted by the increased amount of zooplankton near the cages (Strictar‐Pereira et al, ).…”

“…The excess of nutrients creates a process of artificial eutrophication (Holmer, ; Karydis & Kitsiou, ; White, Phillips, & Beveridge, ), increasing primary productivity and changing trophic interactions (Iriarte et al, ; Pitta et al, ; Sarà et al, ). For the lentic environments, in which cages are usually installed, there are reports of drastic changes in trophic structure and in the balance of phytoplankton (Borges, Train, Dias, & Bonecker, ; Kashindye et al, ), zooplankton (Dias, Takahashi, Santana, & Bonecker, ; Terziyski, Tzavlova, Kalchev, & Iliev, ), benthos (Kashindye et al, ) and fish species (Demétrio, Gomes, Latini, & Agostinho, ; Strictar‐Pereira, Agostinho, & Gomes, ). Specifically, for ichthyofauna, the high availability of artificial food is responsible for the attraction and aggregation of fish in the vicinities of the cages resulting in changes in the structure and functioning of communities (Brandão, Santana, Ramos, & Carvalho, ).…”