Evaluation and economic analysis of fermented fish viscera silage in diets for tambaqui (Colossoma macropomum) and its effects on the physical quality of pellets, growth performance, health parameters.

The production of silage using fish viscera can be carried out with straightforward methods and permits the exploitation of nutrients that are usually discarded. This process fosters the concept of circular aquaculture. The aim of this study was to evaluate the inclusion of increasing levels of fish viscera silage (VS) on the physical quality of the feed pellets and their effects on their growth performance, health parameters and on economic indices when the experimental extruded feed was offered to tambaqui. A fermented fish VS produced in-house was included in increasing levels on a wet-basis in the formulation of five experimental diets (VS 0%, VS 5%; VS 10%; VS 15% and VS 20%). Juvenile tambaqui (~22.6 g) were stocked in fibreglass tanks of 700 L (n = 4; 21 fish per tank) with a recirculation system and the five experimental diets were attributed in a completely randomized design. The fish were fed with the experimental diets (to apparent satiation) for 13 weeks. At the end of the trial, no significant differences were observed for production performance. Fish fed with the highest inclusion level of VS presented the highest concentration of plasma cholesterol, but this was still within acceptable values for this species. The inclusion of fish VS in diets for juvenile tambaqui reduced the activity of the plasma ALT enzyme, confirming normal liver function. Extruded feed containing fish VS had a production cost of US$ 0.95 per kg, which does not significantly impact the economic indices. Up to 20% of fish VS can be included in the extruded feed formulation for juvenile tambaqui without impairing growth performance or affecting health parameters.

Growth performance, hematology parameters and Aeromonas hydrophila challenge of pirarucu (Arapaima gigas) in response to dietary protein levels.

The pirarucu (Arapaima gigas) is a fast-growing Amazonian species of high commercial value. The present study aimed to determine the dietary crude protein (CP) level to promote maximum zootechnical performance for pirarucu fingerlings and as their resistance to Aeromonas hydrophila, as well as evaluate their hematological parameters. Pirarucu fingerlings (2.4 ± 0.08 g, 6.8 ± 0.52 cm) were distributed in 18 tanks (140 L, 40 fish per tank, n = 3) and fed six experimental diets consisting of increasing levels of CP: 300, 400, 450, 500, 550 and 650 g kg-1 in a completely randomized design. Data were submitted to one-way ANOVA (p < 0.05) and the ideal CP level for weight gain was determined using polynomial regression analysis. The dietary CP levels were evaluated using a quadratic polynomial regression and the level of 595 g kg-1 was determined for the best weight gain. The hematocrit of fish fed 300 g kg-1 was higher than in the other groups. No mortalities were observed after the 15-day bacterial challenge; however, number of pirarucu with bacterial damage on the pirarucu caudal fin was higher in the group that was fed the diet with 300 g kg-1. A dietary protein level of 618 g kg-1 is therefore recommended for providing maximum weight gain and immunological resistance in pirarucu fingerlings weighing 2.4-112.5 g.

Changes in gill and air-breathing organ characteristics during the transition from water- to air-breathing in juvenile Arapaima gigas.

The obligate air-breathing Amazonian fish, Arapaima gigas, hatch as water-breathing larvae but with development, they modify their swim bladder to an air-breathing organ (ABO) while reducing their gill filaments to avoid oxygen loss. Here, we show that significant changes already take place between 4 weeks (1.6 g) and 11 weeks (5 g) post hatch, with a reduction in gill lamellar surface area, increase in gill diffusion distance, and proliferation of the parenchyma in the ABO. By using a variety of methods, we quantified the surface area and diffusion distances of the gills and skin, and the swim bladder volume and anatomical complexity from hatch to 11-week-old juveniles. In addition, we identified the presence of two ionocyte types in the gills and show how these change with development. Until 1.6 g, A. gigas possess only the H+ -excreting/Na+ -absorbing type, while 5-g fish and adults have an additional ionocyte which likely absorbs H+ and Cl- and excretes HCO3- . The ionocyte density on the gill filaments increased with age and is likely a compensatory mechanism for maintaining ion transport while reducing gill surface area. In the transition from water- to air-breathing, A. gigas likely employs a trimodal respiration utilizing gills, skin, and ABO and thus avoid a respiratory-ion regulatory compromise at the gills.