Este estudo teve como objetivo avaliar o ganho genético para peso final, e a influência da seleção em outras variáveis zootécnicas e morfométricas, de tilápias-do-nilo selecionadas dentro de diferentes grupos genéticos, após uma geração de seleção individual. Após a seleção, cinco grupos genéticos foram amostrados para realizar o estudo. Foram realizados dez acasalamentos em viveiros de 50 m², separadamente, para cinco grupos selecionados e cinco não selecionados (peixes amostrados da média de peso dos mesmos grupos genéticos para serem utilizados como controle), totalizando dez viveiros. De cada população foram acasaladas 30 fêmeas com 12 machos, totalizando 300 fêmeas e 120 machos. Após 21 dias, foram coletadas as nuvens, das quais 500 larvas por grupo genético foram amostradas, realizando a alevinagem em 10 tanques de 100 L, separadamente para cada grupo, seguido de recria em dez tanques-rede de 1 m³ dentro de um viveiro de 300 m². Posteriormente 30 tilápias (30,0±1,6 g) de cada grupo genético foram marcadas com transponder magnético, totalizando 300 animais. Estes foram distribuídos em três viveiros de 50 m², de modo a ficar 10 animais de cada grupo por viveiro. Após 140 dias de cultivo, os animais foram despescados para avaliação. A seleção individual realizada ocasionou um ganho do peso final do cultivo e no peso do filé de 8,4% e 9,5%, respectivamente. Além disso, os animais selecionados apresentaram aumento no comprimento total, comprimento padrão, altura corporal, largura corporal e comprimento de tronco. Já outras variáveis como sobrevivência do cultivo, rendimento de carcaça, rendimento de filé e comprimento de cabeça, não foram alterados pela seleção para peso final.

Ichthyophthiriasis is a worldwide fish disease with great financial impact on freshwater fish farming due to its associated high mortality rates. Current study assesses the parasiticidal capacity of hydrogen peroxide (H2O2) and chlorine dioxide (ClO2) against the causative agent, Ichthyophthirius multifiliis, in jundiá. Median lethal concentration (LC50, 96h) of each chemical agent was established, as well as the minimum inhibitory concentration of hydrogen peroxide for the parasite´s infectious larval phase (theront). Products were tested asynchronously in parasitized fingerlings for short and long baths at the following concentrations and exposure times: 1. Hydrogen peroxide: (T1) continuous bath - 30ppm and (T2) 50ppm; (T3) short bath - 150ppm, during 1h and (T4) 250ppm during 1h; control group (without any chemical agent). 2. Chlorine dioxide: (T1) continuous bath - 4ppm and (T2) 20ppm; (T3) short bath - 200ppm, during 1min; (T4) short bath - 400ppm, during 1min and control group. Data analysis demonstrated a concentration of 82.54ppm of the commercial product (or 24.76ppm of the active chemical agent) as LC50, 96h of H2O2 and 38.4ppm product (or 2.68ppm of the active chemical agent) for ClO2. Hydrogen peroxide concentration causing 100% mortality rate of theronts in 1h was 25ppm (product, or 7.5ppm of the active chemical agent). At the end of the fourth day of curative experiment, 98% of the animals died by ichthyophthiriasis. No treatment was effective against the parasite.

The economic viability of common snook culture was evaluated from a simulated marine farm with 20 cages of 225m³, with a production cycle of two years, fish with a final weight of 500g and annual production of 45 tons. To scale the production costs, the effectve operating cost (EOC), total operating cost (TOC), total production cost (TPC) were considered.The indices for evaluating profitability were the Internal Rate of Return (IRR), the Return on Capital (RC) and the Net Present Value (NPV). The TPC was USD $305,820 year-1, with USD $6.79 kg-1. Sensitivity analysis by the variation of the feed conversionrate (FCR) reinforces the importance of good production practices, such as adequate food management, use of balanced diets. The factors: juvenile price, feed cost and sales price, more dependent on the market, require a greater ability of the producer to apply commercial and marketing strategies to contain the production cost and avoid the reduction of the sales price. The high cost of installing culture structures and management equipment suggests projects with a minimum rate of attractiveness of 23%, minimum volume of 6,500m³, productivity of 20kg m-³, annual production of 65 tons, FCR below 1.6 and marketing price above USD$8.39 kg-1.

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Two growth stages of juvenile snook (Centropomus undecimalis) under three different densities were evaluated: 10, 20, and 40 fish m-3, in 2.5-m3 cages with 12-mm mesh. In phase I, snooks of 72.0 g and 21.2 cm were raised for 270 days. In phase II, snooks of 204.6 g and 29.2 cm were raised for 202 days. The average water temperature and salinity were 24.3°C and 34.5, respectively, at Santa Catarina Island, Brazil. The data were evaluated using regression models. Density increase did not influence survival rate, with 51.0% (phase I) and 88.7% (phase II). The density of 20 fish m-3 provided the best results, such as body weight, in the two phases, with 215.7 and 364.7 g, respectively. Water temperature was the main limiting factor for the growth of snook. Therefore, in a subtropical climate, it is recommended to start growing in the spring (> 24°C) and avoid handling fish when the temperature is below 20°C. Regression analysis on the final weight showed that densities of 24 fish m-3 could be indicated for common snook under the conditions of this study.