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The objective of this work was to evaluate the use of crude glycerol as an energy source to replace corn, in diets for Nile tilapia (Oreochromis niloticus) in the fattening stage. Two hundred Nile tilapia (190±4.5 g) were distributed in 20 tanks, in a completely randomized design. The treatments consisted of crude glycerol at 0, 60, 120, 180, and 240 g kg-1, to replace the dietary levels of corn, in order to maintain a constant digestible energy. Fish productive performance and the chemical composition of the fillet were evaluated. Histological analyses of the hepatopancreas, intestine, and visceral fat were also carried out. Crude glycerol had no effect on the performance parameters; however, it caused a quadratic reduction of visceral fat. There was an increase in the moisture and a decrease in the ether extract of the fillet. A linear effect on the blood glucose levels was verified in fish fed the diet without glycerol, and the peak occurred at 90 min. There were no differences for measurements of intestinal villi height and hepatocyte area. Crude glycerol can replace corn in diets for Nile tilapia in the fattening stage, without adversely affecting fish metabolism, productive performance, or survival.

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The aim of this study was to evaluate the production performance of Nile tilapia post-larvae and fingerlings fed with increasing levels of alcoholic extract of propolis into diets. In Experiment 1, 1800 post-larvae were distributed in 30 tanks, in a completely randomized design with five treatments composed by the inclusion of 0, 1, 2, 3 and 4 g of dry propolis/kg of feed, and six replicates. In experiment 2, 1600 fingerlings were distributed in the same system and designed as experiment 1. No significant effect was observed between treatments, for final weight, total and standard length, survival, and intestinal villus height. However, the propolis extract inclusion of 1 g/kg in Nile tilapia post-larvae and fingerlings' feed resulted in a better body condition factor and higher body protein deposition (p<0.05). The condition factor is an estimate for the future growth of the animals, possibly the fish treated with propolis extract will present better growth, survival and greater reproductive potential rates. The results of the present study demonstrate that alcoholic extract of propolis improves the nutritional condition of Nile tilapia post-larvae and fingerlings, potentially leading to increased productivity in subsequent stages, as well as leading to improvement in fingerlings muscle deposition.

Intensive aquaculture needs to adopt techniques that are able to contribute towards sustainability. Closed systems that employ water recirculation can combine intensive production with environmental sustainability, since there is no exchange of water or discharge of effluents into the environment. In order to achieve this, effective filtration systems are required to ensure that the water quality is satisfactory for the cultivation of aquatic organisms. Chitosan, an industrial waste material derived from crustacean farming, is a renewable natural material that is biodegradable and possesses adsorbent characteristics. In this work, chitosan foam was incorporated in filters and was evaluated as an adsorbent of aquaculture pollutants, adding value to the material and at the same time providing a use for industrial waste. The foam was characterized by scanning electron microscopy and energy dispersive spectroscopy, apparent density, and water absorption capacity. It was used to remove ammonia, nitrite, orthophosphate, and turbidity from aquaculture effluents. The foam consisted of a bilayer with smooth and porous sides, which presented low density, flexibility, and high water absorption capacity. The best proportion of the foam, in terms of the mass of foam per volume of solution (% m v), was 0.10, which resulted in removal of 32.8, 57.2, 89.5, and 99.9% of ammonia, nitrite, orthophosphate, and turbidity, respectively. This biopolymer produced is biodegradable, and when saturated with organic compounds from aquaculture, and no longer suitable for reuse as a filter material, it can be employed as a fertilizer, hence closing the sustainability cycle of the aquaculture production chain.

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Crude glycerol and its purified and synthesized forms derived from biodiesel production are non‐toxic, biodegradable, biocompatible and versatile, and can be converted into various chemicals or products for biological use. Among the possible uses, there is its use in fish feeding, due to the chemical and nutritional composition, for being classified as energetic food and has low cost. The possibility of using glycerol in fish diets has been motivated by increasing maize prices, the excessive amount of glycerol produced and its processing costs for other purposes. Glycerol use in fish diet formulations is feasible, provided that certain factors be evaluated, such as digestibility and inclusion levels. In this context, this review discussed the main aspects that must be taken into account regarding glycerol use in fish diets, such as the characteristics and chemical composition of its categories, their fish metabolism pathways and their influence on fish plasma glucose. Crude glycerol or glycerine displays good potential for use in fish feed, as it contains adequate energy concentrations and can replace part of fish feed maize. However, it is evident that assessments concerning specific physiological phases, such as fish in reproductive phases, as well glycerol stability in water, are required.