Eudes de Souza Correia

Effect of pond aging on natural food availability and growth of the freshwater prawn Macrobrachium rosenbergii

Abstract Most farmed prawns are cultured in earthen ponds in semi-intensive systems, with added feed. Newly dug ponds have low biomass and diversity of microbial and macroinvertebrate populations and therefore require adequate fertilization programs to improve the ponds’ natural productivity. Once established, ponds contain microbial and macroinvertebrate populations that are of high nutritional value to the prawns. The aim of this study was to examine the effect of pond aging on natural food production and its availability, and how it affects the growth performance of the prawn Macrobrachium rosenbergii. Experiments were conducted in 50-m2 earthen ponds which were treated with hydrated lime, followed by organic and inorganic fertilization to obtain an adequate natural productivity level. Post-larvae were stocked in new ponds (pond age: 1–3 months) and in old ponds (pond age: 8–10 months) at a weight of 0.05 and 0.06 g, respectively, and stocking density of 80 and 72 animals/m2, respectively. The prawns were cultured for 63 days, and were subjected to one of two treatments: offering artificial feed during the last 42 days of culture (treatment 1) or during the last 21 days of culture (treatment 2). In new ponds the juveniles grew in average 22 and 11 mg/day, respectively, for the 42 and 21 days of feeding treatments. In old ponds, utilizing the same conditions, the prawns grew significantly better (P⩽0.05), averaging 48 and 21 mg/day, respectively, for the 42 and 21 days of feeding treatments. This is equivalent to prawn weight gain of 121 and 93% and biomass increase of 74 and 53% for the 42 and 21 days feeding treatments, respectively, in the older ponds over that of the new ponds. The improved growth in the old ponds correlated with an increase in the density and diversity of benthic macroinvertebrate, as evidenced by the increased numbers of zoobenthos in the old ponds and in greater diversity of food items found in the stomach contents of the prawns in the old ponds. The present work demonstrates a clear advantage of pond aging as applied to the culturing of M. rosenbergii in earthen ponds. Further work is needed in order to develop innovative techniques to shorten the pond aging process as it relates to the ponds microbial and macroinvertebrates populations.

Cultivo da tilápia do Nilo Oreochromis niloticus em sistema de bioflocos com diferentes densidades de estocagem

Objetivou-se com este trabalho avaliar a qualidade da agua e o desempenho zootecnico da tilapia do Nilo (Oreochromis niloticus) cultivada em sistema de bioflocos sob diferentes densidades de estocagem. O experimento foi conduzido na Estacao de Aquicultura da Universidade Federal Rural de Pernambuco, Brasil, durante 128 dias. Peixes de 123,0±0,6g foram estocados em 12 tanques circulares (800 L) em um delineamento inteiramente casualizado com tres tratamentos (D15, D30 e D45, correspondendo as densidades de 15, 30 e 45 peixes.m-3) e quatro repeticoes. Entre as variaveis de qualidade de agua, o oxigenio dissolvido teve efeito significativo (P≤0,05) entre as densidades, com a menor concentracao (3,97 mg O2.L-1) na maior densidade testada (45 peixes.m-3). A amonia total apresentou diferenca estatistica (P≤0,05) entre o tratamento D15 e os demais; e o nitrito, entre a densidade de 15 e 45 peixes.m-3, porem ambos numa relacao diretamente proporcional com o aumento da densidade de estocagem, apresentando maiores concentracoes medias de 2,56 e 3,26 mg.L-1 de amonia e nitrito, respectivamente, na densidade de 45 peixes.m-3. O desempenho zootecnico, no tratamento D45 apresentou melhor resultado, com produtividade de 16,6 Kg.m-3, com diferenca significativa entre os tratamentos (P≤0,05). A sobrevivencia foi superior a 90% nas tres densidades testadas. A tecnologia de bioflocos pode ser empregada no cultivo intensivo da tilapia do Nilo O. niloticus na fase de engorda, utilizando-se densidades de estocagem de 45 peixes.m-3.

Substituição do óleo de peixe por óleo de soja em dietas para beijupirá (Rachycentron canadum)

The replacement of fish oil for cobia (Rachycentron canadum) in diets was evaluated using five proportions of fish oil:soybean oil. Two hundred juveniles (±12g) were randomly distributed in twenty 480L tanks and fed to apparent satiety twice daily for 42 days. Diets contained 12% lipids with different proportions of fish to soybean oils and were therefore named OP0, OP25, OP50, OP75 and OP100 according to the inclusion content of fish oil (0, 25, 50, 75 and 100%, respectively). Increasing dietary fish oil levels resulted in higher survival, growth and feed intake. Fish fed diets OP75 and OP100 presented higher weight gain than those fed diets OP0 and OP25, whereas fish fed diet OP50 had an intermediate weight gain. Overall, performance was enhanced at higher contents of dietary fish oil. No significant differences on protein and lipid content of fish carcass were observed, but moisture and ash content differed significantly between treatments. The inclusion of relatively higher contents of plant ingredients affected feed intake, which resulted in lower growth rates. The present results suggest the possibility of replacing up to 50% of fish oil with soybean oil in diets for cobia juveniles.

Culture of Nile tilapia in a biofloc system with different sources of carbon

The aim of this work was to evaluate the effects of using different sources of organic carbon on water quality, growth performance and the acceptability of Nile tilapia (Oreochromis niloticus) fillets grown in a biofloc system. The experiment was carried out over 145 days at the Aquaculture Station of the Federal Rural University of Pernambuco, Brazil. Fish of 72.6 ± 6.83 g were stored (35 fish m-3) in 19 circular tanks (800 L) in a completely randomised experimental design with three treatments, including as a source of carbon, sugar (SUG), liquid molasses (MOL) and molasses powder (MOP), each with five replications, and one control treatment (CTL) without bioflocs, with four replications. Dissolved oxygen concentrations were significantly higher (P≤0.05) in the tanks with no bioflocs due to the absence of bacterial biomass. Total ammoniacal nitrogen (TAN) showed a statistical difference (P≤0.05) between the SUG treatment and the other treatments with bioflocs, having the lowest concentration of 2.53 mg L-1. Survival was greater than 80%, with no statistical difference between treatments (P>0.05); productivity varied from 9.72 (SUG) to 14.22 kg m-3 (CTL) (P≤0.05). Water consumption in the tanks with bioflocs was 11.8 times lower than in the control (CTL). The tilapia fillets from the bioflocs with sugar were preferred by the evaluators, with a score of 7.77 (like moderately to like very much). The carbon sources used (molasses and sugar) can be employed in the culture of O. niloticus tilapia in bioflocs with no damage to the culture water or to productivity.

FONTES DE CARBONO E RELAÇÕES C:N NA QUALIDADE DA ÁGUA NO CULTIVO DE TILÁPIA DO NILO EM SISTEMA DE BIOFLOCO

The use of biofloc technology (BFT) can improve fish production in regions with low water availability. Therefore, information on dynamics of water quality is essential for success in fish rearing. Thus, the objective of the present study was to evaluate the water quality for Nile tilapia farming in a system without water exchange, during the fingerling stage, using different sources of carbon and C:N ratios. A completely randomized experimental design was used in a 2x3 factorial arrangement, with two carbon (C) to nitrogen (N) ratios (10:1 and 20:1) and three carbon sources (sugar, molasses and cassava starch). The C:N ratio and carbon source affected the variables alkalinity, settleable solids (SS), turbidity and total suspended solids (TSS), showing significantly higher values at C:N ratio of 20:1 (P < 0.05). The best carbon source for microbial floc formation were the molasses and sugar, under C:N ratios of 10:1 and 20:1. The stability of the monitored water quality parameters occurred from 6 to 7 weeks of rearing. The growth performance of Nile tilapia in BFT system fertilized with different organic carbon sources was not significantly different (P < 0.05) between treatments. The use of molasses to fertilize BFT systems can reduce costs of production in regions where this product is available.