Net cages enhance golden mussel (Limnoperna fortunei) larval density and condition factor

Abstract

Cage fish farming is an important economic activity in Brazil where tilapia (Oreochromis niloticus) is the main cultivated species. To investigate the cage fish farm as a vector for golden mussel invasion, we hypothesised that: (1) Limnoperna fortunei, a freshwater bivalve mollusc, finds greater food availability in the cage fish farm; (2) the cage fish farm favours mollusc colonisation and its nutritional status; and (3) its performance in the reservoir would vary over the year. We obtained data from limnological variables as well as the number of larvae and adult individuals, to evaluate condition index (CI) monthly from February 2015 to January of 2016. We established sampling stations at three points with fish farming and three points without fish farming (controls) in the Canoas II Reservoir, Paranapanema River, Brazil. We used principal component analysis (PCA) to identify spatial and temporal distribution of samples according to limnological variables. We performed a linear mixed model analysis to test the hypothesis of no difference between areas (fish farm and control) and time (months) for larval density and CI of L. fortunei. The first PCA axis (28.48% of variance) revealed a temporal gradient, showing the separation between cold and hot months. The second PCA axis (19.61% of variance) separated the samples of control and fish farms; fish farms displayed higher concentrations of total phosphorus, nitrite, and chlorophyll a. Larval densities of L. fortunei were higher in fish cage areas with time being responsible for 35% of this variation. Mussel CI was also higher in fish farms and time was responsible for 36% of the variation. We conclude that fish production in cages contributes to the establishment of golden mussels in the reservoir. Our results serve as a warning that other molluscs or invasive species may be favoured by aquaculture activities in aquatic environments. The colonisation of the mussel in the reservoir varies during the year in response to seasonality.

Bioaccumulation of Metals and Evaluation of Golden Mussels Encrusted on Different Screens of Net Cages

“…Boltovskoy and Cataldo (1999) found that mussels show accelerated growth during summer and reduced growth in winter, while Santos et al (2008) observed a greater growth of the golden mussel during the spring and summer. Furthermore, Rezende Ayroza et al (2019) confirmed that fish farming in net cages favors colonization and nutritional status of L. fortunei and its performance in the reservoir varies during the year in response to seasonality.…”

“…Pollution can originate from domestic sewage, garbage, agricultural and livestock waste, which can cause changes in water quality, eutrophication, and bioaccumulation of heavy metals, among others. The golden mussel can be a bioindicator that allows evaluating pollutions in the aquatic environment and the influence of the intensive system of fish in net cages in the environment since this cultivation system generates a supply of nutrients and minerals that can have negative effects on the existing fauna (Marengoni et al, 2013;Rezende Ayroza et al, 2019).…”

“…Furthermore, the fouling blocks water exchange from net cage and biologically analyzing can be a source of contamination or pollution for aquaculture in reservoirs (Costa et al, 2018;Freire and Marafon, 2018;Vianna et al, 2019). Rezende Ayroza et al (2019), when investigating the cage fish farm as a vector for golden mussel invasion, concluded that fish breeding in cages contributes to the establishment of the L. fortunei in reservoirs by elevating larval density and the nutritional status of the mollusk. The colonization of this freshwater bivalve mollusk in the reservoir varies during the year in response to seasonality.…”

Limnoperna fortunei colonization and macrofouling on net cages in a subtropical reservoir (Brazil)

“…Consequently, native communities and anthropic activities, such as hydroelectric and nuclear power plants (Boltovskoy et al, 2013;Cataldo et al, 2003;Darrigran et al, 2007) and fish farming in net cages in Brazil (De Rezende Ayroza et al, 2019), are affected. Limnoperna fortunei's fertilization is external, and its larval development is divided into two main stages: non-valvular, after fertilization until the formation of the trocophorous larva, and valvular, from veliger to plantigrade or pediveliger larva, when the planktonic phase ends.…”

“…In the state of São Paulo, the third largest producer of Brazilian fish, Costa et al, (2018) calculated that the removal of mollusks fixed to the screens using a high-pressure device can lead to an increase of up to 27% in the cost of fish production. On the other hand, De Rezende-Ayroza et al, (2019) demonstrated that fish farming in cages favors the colonization of L. fortunei and ensures its nutritional status. They report that larval density and Condition Index in these areas were higher compared to control areas, particularly in the hottest period, because of higher concentrations of total phosphorus, nitrite, ammonium-N and chlorophyll a.…”