Imbalanced C/N - controlled, periphyton-based system has hampered tilapia growth in stagnant experimental tanks

Rafael Barroso Martins,Diego Alves Do Vale,Marcelo Vinícius Do Carmo E Sá,Vanessa Tomaz Rebouças

doi:10.4025/actascitechnol.v36i2.19515

Rafael Barroso Martins, Diego Alves Do Vale + Show 2 more

Open Access

https://doi.org/10.4025/actascitechnol.v36i2.19515

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Abstract

The simultaneous use of periphyton and controlled C/N ratio of water may improve water quality and fish growth. The current assay investigated the interaction between periphyton and C/N ratio of water in rearing tanks with Nile tilapia juveniles. The study was carried out in 20 outdoor stagnant 250- L tanks. A wooden structure for periphyton development was submerged in five of the tanks. A completely randomized 2 x 2 factorial mode design was employed to evaluate the following factors: (1) substrate for periphyton and (2) the C/N ratio of water. Dry molasses were applied weekly in the tanks to raise C/N ratio of water to 20:1. The addition of molasses to the culture water significantly lowered DO2 and pH levels of water, and raised nitrite concentration. Fish stocked in the control tanks (no periphyton, no C/N ratio balance) attained a final body weight significantly higher than those observed for other treatments after 6 weeks of culture. In spite of the correction of C/N ratio of water to 20: 1, low DO2 concentrations avoided the suitable development of bioflocs.

Highlights

There is currently a great concern on the possible environmental impacts of aquaculture
The temperature of culture water at 0800 and 1600h during the experimental period ranged between 25.4 and 26.9°C and between 27.4 and 29.9°C, respectively. These temperatures were within the range for normal tilapia growth (AZAZA et al, 2008)
No significant difference in electrical conductivity (EC) was reported between the tanks

Summary

Introduction

There is currently a great concern on the possible environmental impacts of aquaculture. It is well known that fish farm’s effluents are nutrient rich, especially for nitrogen and phosphorus. If released directly into the receiving water bodies, fish farm effluents may cause eutrophication and, deterioration and loss of biodiversity (LEFRANÇOIS et al, 2010). Among the proposed solutions to the eutrophic fish farm effluents problem, the employment of culture systems based on minimal or even no water. These systems rely on the self-cleaning capacity of tanks which should be suitably stimulated by appropriate methods. The biological processes that remove nutrients from the culture water, such as photosynthesis and heterotrophic bacteria (bioflocs) growth, are suitably promoted in those systems (AZIM; LITTLE, 2008)

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