Influence of net-cage fish farming on zooplankton biomass in the Itá reservoir, SC, Brazil

Abstract

OBJECTIVES: This study aimed to verify the influence of net-cage fish farming on zooplankton biomass in the Itá reservoir (Uruguay River, Brazil). METHODS: Samples were collected monthly from October/2009 to May/2010 at the surface and at the bottom in two sampling stations, the net-cage area and in a control area using a Van Dorn bottle and a plankton net (68 µm). RESULTS: The Cladocera and Copepoda biomass was estimated by dry weight using a micro-analytical balance, and the Rotifera biomass by Biovolume. Total zooplankton biomass varied between 6.47 and 131.56 mgDW.m-3 Calanoida copepod presented the highest value of biomass (127.56 mgDW.m-3) and rotifers, despite having an important contribution to total density, showed a maximum biomass of 2.01 mgDW.m-3. Zooplankton biomass at the net-cage area surface was higher when compared with the control area during the months of October to January. However, the zooplankton biomass was similar at the bottom of the two areas throughout the studied period. From February until May, zooplankton biomass decreased in both sampling stations, a fact probably associated with the flushing of the reservoir, followed by an increase in water transparency and a decrease in chlorophyll-a concentration in the following months (February to May). CONCLUSIONS: The influence of fish farming on zooplankton biomass was detected at the surface of the net-cage area only from October to January. From February to May this influence was not found, probably by the influence of the flushing of the reservoir.

Towards Integrated Multi-Trophic Aquaculture: Lessons from Caprellids (Crustacea: Amphipoda)

“…In this case, the availability of detritus for caprellids is guaranteed, and the additional TAG, PC and MUFA requirements of juveniles and reproductive females could be obtained by preying on copepods or other small planktonic crustaceans, which naturally inhabit fish farm ecosystems. Copepods are among the dominant groups inhabiting the plankton communities of fish farms [ 69 ] and their biomass at net-cage areas can be higher when compared with control areas [ 70 ].…”

Environmental conditions are more effective than nutrient availability and spatial processes on explaining microphytoplankton functional structure in a subtropical hypereutrophic reservoir

“…The reservoir was formed in the early 2000's, when a dam was built in the main course of the Uruguay River to provide water flow to the It a Hydroelectric Power Plant (It a HPP), the fourth in a reservoir cascading system built in the upper portion of the Uruguay River watershed. The reservoir has a surface area of 141 km 2 , a maximum depth of 125 m and an average depth of 36 m. The retention time is 55-60 days, according to the season of the year (Loureiro et al 2012;Lima et al 2017). The region's climate is classified as wet subtropical (Cfa and Cfb) in Koppen's system, with annual mean precipitation ranging between 1900 and 2200 mm (Alvares et al 2013).…”

Cage fish farm act as a source of changes in the fish community of a Neotropical reservoir

“…This aggregation can affect fish fauna by restructuring animal communities, favoring a few species (Bartozek et al, 2014;Dempster and Sanchez-Jerez, 2004;Loureiro et al, 2011;Menezes and Beyruth, 2003), improving fishing pressure in the vicinity (Akyol and Ertosluk, 2010;Bagdonas et al, 2012) or altering their diet and populational attributes (Brandão et al, 2013;Brandão et al, 2012;Ramos et al, 2013). However, most of studies were performed in marine environments (Bacher et al, 2012;Dempster and Sanchez-Jerez, 2004;Dempster et al, 2002;Izquierdo-Gomez et al, 2015;Machias et al, 2005;Machias et al, 2004;Özgül and Angel, 2013;Sanchez-Jerez et al, 2011).…”