Effects of nutrients increase on the copepod community of a reservoir using cages

Vanessa Graciele Tibúrcio,Fábio Amodêo Lansac-Tôha,Leilane Talita Fatoreto Schwind,Rodrigo Leite Arrieira,Claudia Costa Bonecker

doi:10.1590/s2179-975x0315

Vanessa Graciele Tibúrcio, Fábio Amodêo Lansac-Tôha + Show 3 more

Open Access

https://doi.org/10.1590/s2179-975x0315

Copy DOI

Abstract

Abstract Aim: This study investigated changes in copepod abundance and the influence of environmental variables in a reservoir with fish farming using cages, on temporal and spatial scales. We hypothesised that the copepod abundance will increase when influenced by changes in environmental variables due the increase of nutrients originating from fish farming. Methods A 120-day sampling of copepods and environmental variables was carried out in a subtropical reservoir of the Paraná River basin (Rosana reservoir), upstream and downstream of three sets of cages with different fish stocking densities. A Principal Component Analysis was conducted to characterise sampling periods and points through environmental variables. The differences between copepod abundance according to sampling periods and points were tested by ANOVA. Results We observed higher maximum values for most nutrient concentrations and dissolved oxygen in the final stage of the experiment and in the location of cages installation. The copepod abundance increased sharply during the first days of the experiment and then decreased during the following periods with a tendency towards returning to the initial conditions at the final stage of the experiment. A significant difference in copepod abundance between the location of cages installation and downstream was showed. In addition, turbidity, chlorophyll-a, and nitrate significantly predicted copepod abundance. Conclusion The results suggested that the changes in copepod abundance over time are influenced by environmental variables, evidenced by the increase in nutrient concentration after the cage installation, related to the increase in the practice of fish farming. The environmental variables related to system productivity were linked to the availability of food resources. Thus, our hypothesis that copepod abundance is increased due the alterations in environmental variables caused by the increase in the practice of fish farming using cages was corroborated.

Highlights

Fish farming using cages is a major emerging aquaculture modality in Brazilian reservoirs (Ayroza et al, 2006); the technique is relatively cheap and simple compared to traditional fish farming using earthen ponds for enabling the use of a large variety of aquatic environments such as reservoirs, and discards the costs of pond construction (Rotta & Queiroz, 2003)
The environmental variables values presented no significant differences between grouped points in each studied period
The environmental variables values presented no significant differences between grouped points in each studied location

Summary

Introduction

Fish farming using cages is a major emerging aquaculture modality in Brazilian reservoirs (Ayroza et al, 2006); the technique is relatively cheap and simple compared to traditional fish farming using earthen ponds for enabling the use of a large variety of aquatic environments such as reservoirs, and discards the costs of pond construction (Rotta & Queiroz, 2003) It is a very intensive type of farming that employs a considerable volume of food inputs for fish production using reduced space under a high fish density, which releases food waste and metabolites directly into the environment (Beveridge, 1984). In a previous study, Arrieira et al (2015) emphasised that environmental variables are major structuring factors for communities of testate amoeba in aquatic environments; the assessment of the environmental characteristics of water (physical, chemical and biological variables) may be a good predictor to analyse the variability and structure of communities in freshwater environments (Neiff, 1996)

Objectives

Methods

Results

Conclusion