The search for new sustainable aquafeeds for the species with greater economic importance, such as the gilthead sea bream in Europe, is one of the main challenges in the aquaculture sector. The present work tested fishmeal replacement by a mixture of plant meals at different levels, as well as the use of marine by-products with attractant properties and high-quality protein in high plant protein diets. In order to do that, effects on growth and biometric parameters, digestibility, amino acid retention, excreted ammonia and proteases and amylase activity were assessed, using six different diets: FM100 (100% of protein provided by fishmeal), FM50 (50% of replacement), FM25 (75% of replacement) and FM0 (100% of replacement), but also FM25+ (75% of replacement and 15% of squid and krill meal inclusion), and FM0+ (100% of replacement and 15% of squid and krill meal inclusion). In group FM0, a clear impact of dietary changes was observed on growth, survival and ammonia excretion. Amino acid retention in group FM0+ was also significantly affected, which can be explained by the limited content of certain amino acids in this diet. On the other hand, no significant differences were observed in most biometric parameters or in enzyme activity. In conclusion, complete fishmeal replacement can be achieved by using a mixture of plant-based sources, but supplementation with complementary marine ingredients can prevent detrimental effects on growth, survival, nutritional parameters and protein metabolism.

A 154‐day trial was performed to assess the use of an alternative protein blend (corn gluten, krill and meat meal) as a substitute for fishmeal in diets for juvenile yellowtail, using four isolipidic (140 g/kg) and isoenergetic diets (24 MJ/kg) with the same digestible protein content (50%). The control diet was FM100, without replacement, and in FM66, FM33 and FM0, fishmeal was replaced at 33 g/kg, 66 g/kg and 100 g/kg, respectively. At the end of the experiment, no differences in growth parameters were observed. Fish fed the FM0 diet exhibited the lowest survival (23%). This high mortality may be due to different factors, such as a dietary amino acid imbalance or some antinutrient factors contained in the alternative ingredients. Feed intake, feed conversion ratio, digestible protein intake and protein efficiency ratio were similar in all diets. However, digestible energy intake and protein efficiency retention were lowest in fish fed the FM0 diet. Apparent digestibility coefficients for protein, energy and amino acids diminished as a substitution for fishmeal increased. Significant differences were observed in the diet whole‐fish body profile amino acid retention (AAR) ratio for the seven essential amino acids. In summary, total fishmeal replacement by the blend assayed was not feasible for yellowtail. The FM66 diet resulted in good growth, high survival and good nutrient efficiency.

In recirculating aquaculture systems, performance of nitrifying biofilters for total ammonia nitrogen (TAN) removal from the culture water and thus minimizing eutrophication depends on numerous elements of design. In this article the combined effect of three of these process parameters (temperature, hydraulic loading and TAN load) is evaluated. Ammonia removal rates (N-TAN divided by biofiltration area and day) were measured for every combination of five different temperatures, three different hydraulic loadings and three different ammonia loads. Every one of the process parameters were influential on nitrification rates and the lowest process parameters values corresponded with significantly lower N-TAN removal rates. A significantly higher mean N-TAN removal rate (0.241 gN-TAN removed m -2 day -1 ) was found for the combination of the highest water temperature (27 ºC), the highest hydraulic loading (11 2 m 3 m -2 h -1 ) and the highest TAN load (9 gTAN m -3 day -1 ), suggesting a positive synergy of the three process parameters on the achievement of greater biofilter performances.

ElsevierGodoy-Olmos, S.; Martínez-Llorens, S.; Tomas-Vidal, A.; Jover Cerda, M. (2016). Influence of filter medium type, temperature and ammonia production on nitrifying trickling filters Notes: Full names separated by dashes indicate both surnames used in Spain. Initial letters stand for given names. ABSTRACTThis work focuses on the achieving of optimal design and modelling of nitrifying trickling filters for closed circuit aquaculture turbot (Psetta maxima) farms. Several process parameters influential in nitrifying filtration were established on experimental biofilters and their efficiency was tested, based on the removal of nitrogen contained in total ammonia nitrogen (N-TAN) in a fixed time (24 hours). Those process parameters were filter media types (Type A Biofill®, BactoBalls® and MECHpro® rings), temperatures (24.3ºC, 19.0ºC, 15.3ºC) and production of TAN (1.5, 3.0 and 4.5 g per day) while other process parameters values remained constant. TAN production was simulated with the addition of ammonium chloride (NH4Cl) in the recirculation system. Constant measuring of the total ammonia nitrogen concentration in the biofilter effluent was required to perform a model of N-TAN fluctuation based on a specific feeding regime and to ascertain performance differences between biofilters.At the end of the experiment, notable differences were observed in the ammonia removal rates depending on different process parameters. The BactoBalls® filter medium led to the highest mean N-TAN removal rates (0.24 g N-TAN removed m -2 day -1 ). The N-TAN removal rate generally increased with higher temperatures, the trials with the highest mean temperature (24.3ºC) led to the highest mean N-TAN removal rate (0.26 g N-TAN removed m -2 day -1 ). Similarly, the N-TAN removal rate increased with high TAN production. The trials in which production was 4.5 g per day showed the highest N-TAN mean removal rate (0.27 g N-TAN removed m -2 day -1 ).

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