Characterization and evaluation of the impact of feed management on the effluents of Nile tilapia (Oreochromis niloticus) culture

O objetivo deste trabalho foi avaliar o efeito da utilização de diferentes manejos alimentares: alimento natural, ração peletizada, extrusada ou farelada, sobre a qualidade da água dos efluentes gerados em uma criação de tilápia do Nilo (Oreochromis niloticus). O experimento foi desenvolvido durante 19 semanas em doze viveiros de 300 m², com renovação contínua de água, povoados com juvenis machos de tilápia do Nilo na densidade de 1,7 peixes m-2. As rações isoproteícas (30% de proteína bruta) e isoenergéticas (3.000kcal de energia digestível) foram fornecidas duas vezes ao dia. Quanto ao tratamento alimento natural, foi utilizado esterco de galinha poedeira. Semanalmente, foram aferidos na água de abastecimento e nos efluentes, temperatura, oxigênio dissolvido, pH, fósforo total, nitrogênio total, clorofila a e material em suspensão. de maneira geral, houve piora na qualidade da água dos efluentes de todos os tratamentos estudados, em comparação a água de abastecimento, evidenciando o impacto ambiental desta atividade produtiva, podendo levar a eutrofização dos corpos d'água receptores.

Acute lethal and sublethal effects of neem leaf extract on the neotropical freshwater fish Prochilodus lineatus

The aim of this study was to determine the toxicity of the aqueous extract of neem leaves, a product extensively used in fish-farms as alternative for the control of fish parasites and fish fry predators, for the neotropical fish Prochilodus lineatus. The 24 It LC(50) of neem leaf extract for juveniles P lineatus was estimated as 4.8 g L(-1); the fish were then exposed for 24 h to 2.5, 5.0 and 7.5 g L(-1) or only clean water (control). Plasma glucose levels were higher in fish exposed to 2.5 g L(-1) and 5.0 g L(-1) neem extract, relative to control, indicating a typical stress response. Neem extract did not interfere with the osmoregulating capacity of the fish, as their plasma sodium, chloride, total protein and osmolarity did not change. The presence of the biopesticide interfered with the antioxidant defense system of P. lineatus, as there was a decrease in liver catalase activity at all neem concentrations and the detoxifying enzyme glutathione-S-transferase was activated in fish exposed to 5.0 g L(-1). Fish exposed to all neem extract concentrations exhibited damaged gill and kidney tissue. These results indicate that although neem extract is less toxic to P. lineatus than other synthetic insecticides used in fish-farming it does cause functional and morphological changes in this fish species. (c) 2006 Elsevier B.V. All rights reserved.

Seasonal variations in chemical composition and stable isotopes of farmed and wild Brazilian freshwater fish

This study examined variations in the Fulton condition factor, chemical composition, and stable isotopes of carbon and nitrogen in the Brazilian freshwater fish cachara (Pseudoplatystoma fasciatum), comparing farmed and wild fish in different seasons. Values for energy, protein, moisture, and Fulton's condition factor were higher for farmed than for wild fish in the rainy season, indicating better nutritional quality; however, these differences were not observed in the dry season. Likewise, we found significant enhancement of delta(15)N in farmed fish in the rainy season but not in the dry season, whereas enhancement of delta(13)C was observed in both seasons. The combined measurement of delta(13)C and delta(15)N provided traceability under all conditions. Our findings show that stable isotope analysis of C and N can be used to trace cachara origin, and that seasonal variations need to be considered when applying chemical and isotopic authentication of fish and fish products. (C) 2010 Elsevier Ltd. All rights reserved.

Eutrofização e qualidade da água na piscicultura: consequências e recomendações

The eutrophication (cultural or anthropogenic) is induced by man and can have different origins, such as domestic sewage, industrial and agricultural activities, including the effluent still breeding systems of aquatic organisms. The expansion of aquaculture, with production of biomass and increase of nutrients in water may cause acceleration of productivity of algae, changing the ecology of aquatic systems. In addition, these waste water may present a risk to health through the transfer of pathogens from manure, plant residues, composted material, among others that are major sources of organic waste in some farming systems. Depending on the trophic level of fish ponds, which are dynamic environments, different planktonic species with short reproductive cycle and adapted to the changes contained in these systems can appear in high abundance. Water quality in the systems for raising fish is related to several factors, such as water source, management (liming, fertilizing, cleaning), cultivated species and quantity and composition of exogenous food. In order to minimize environmental impacts, there are techniques to improve the quality of water in fish farming systems and thus satisfactory answers can be obtained through the application of management practices. This paper aims to review the subject that deals with changes in water quality resulting from the activity of freshwater fish culture in Brazil. Search also recommend techniques of good management practices to minimize the impact generated by the activity.