Inclusion of macroalgae meal (Macrocystis pyrifera) as feed ingredient for rainbow trout (Oncorhynchus mykiss): Effect on flesh fatty acid composition

Intestinal inflammation is a harmful condition in fish that can be triggered by the ingestion of soybean meal. Due to the positive costs-benefits ratio of including soybean meal in farmed fish diets, identifying additives with intestinal anti-inflammatory effects could contribute to solving the issues caused by this plant protein. This study evaluated the effect of incorporating lactoferrin (LF) into a soybean meal-based diet on intestinal inflammation in zebrafish. Larvae were fed with diets containing 50% soybean meal (50SBM) or 50SBM supplemented with LF to 0.5, 1, 1.5 g/kg (50SBM+LF0.5; 50SBM+LF1.0; 50SBM+LF1.5). The 50SBM+LF1.5 diet was the most efficient and larvae had a reduced number of neutrophils in the intestine compared with 50SBM larvae and an indistinguishable number compared with control larvae. Likewise, the transcription of genes involved in neutrophil migration and intestinal mucosal barrier functions (mmp9, muc2.2, and β-def-1) were increased in 50SBM larvae but were normally expressed in 50SBM+LF1.5 larvae. To determine the influence of intestinal inflammation on the general immune response, larvae were challenged with Edwardsiella tarda. Larvae with intestinal inflammation had increased mortality rate compared to control larvae. Importantly, 50SBM+LF1.5 larvae had a mortality rate lower than control larvae. These results demonstrate that LF displays a dual effect in zebrafish, acting as an intestinal anti-inflammatory agent and improving performance against bacterial infection.

The e¡ect of dietary inclusion of whole grain white lupin (Lupinus albus) on growth performance, histology, muscle fatty acid composition and nutrient digestibility was investigated in an 11-week growth and a 4-week digestibility trial with rainbow trout (initial body weight of 54.0 AE 6.2 and 181.9 AE 3.4 g respectively). Four experimental extruded diets were formulated to contain 0%, 30%, 40% and 50% of whole grain lupin and fed to triplicate groups of ¢sh twice a day until apparent satiation. Faeces were collected daily from each digestibility tank by decantation. No signi¢cant trends were observed with respect to growth, feed utilization, apparent digestibility coe⁄cients or whole-body composition (P40.05). Conversely, increasing levels of dietary lupin led to signi¢cant decreases in the Hepatosomatic index (R 2 50.75, Po0.05) and slight lipid in¢ltration into hepatocytes and enterocytes. Muscle fatty acid compositions were slightly a¡ected by the dietary treatment. Polynomial regression of dietary inclusion of lupin and muscle fatty acid concentrations showed an increase in C18:1n-9, C18:2n-6 and C18:3n-3 and a decrease in C20:5n-3 with increasing dietary lupin level. These results demonstrated that whole grain lupin can be included up to 50% in commercial rainbow trout diets without negative e¡ects.

Atlantic salmon (Salmo salar) is a carnivorous fish species whose productive performance tends to be suboptimal when fed low-cost carbohydrate rich meals. It is of interest to study the dynamics of gut microbiota communities in salmonids fed high carbohydrate diets since gut microbes are referred to as key players that influence the metabolism and physiology of the host. A study was conducted to determine the effect of feeding a high carbohydrate diet to Atlantic salmon in gut microbiota communities. A medium carbohydrate (15% wheat starch)/medium protein (MC/MP) diet or a high carbohydrate (30% wheat starch)/low protein (HC/LP) diet was fed to triplicate tanks (28 fish each) during four weeks. We conducted an in-depth characterization of the distal intestine digesta microbiota using high-throughput sequencing of the V4 region of the 16S rRNA gene. Firmicutes, Actinobacteria and Proteobacteria were the major phyla determined in either experimental group. Phylum Planctomycetes, class Planctomycetia, order Planctomycetales and genus Lactococcus were significantly more abundant in fish fed the HC/LP diet compared with fish fed the MC/MP diet. Our study suggests feeding a carbohydrate rich meal to salmon exerts a low impact on the structure of gut microbial communities, affecting mostly low-abundance bacteria capable of metabolizing anaerobically carbohydrates as a major energy-yielding substrate.

Galaxias maculatus eggs and larvae obtained from broodfish captured either in an estuarine or a freshwater environment, as well as from cultured broodstock were analysed to compare their lipid and fatty acid profiles. Results showed a lower lipid content in embryos and larvae from estuarine populations than those from fresh water, denoting the influence of environmental conditions. The n-3:n-6 ratio was higher in eggs from estuarine and cultured populations, being in the range of marine fishes, whereas for eggs from freshwater fish was lower and typical of freshwater fishes. The polyunsaturated fatty acids (PUFA), particularly docosahexaenoic acid (22:6n-3) and eicosapentaenoic acid (20:5n-3), were higher in eggs and larvae of broodstock coming from culture or estuarine environments than in those from fresh water. Moreover, these fatty acids markedly increased after hatching in larvae coming from estuarine populations, suggesting the effect of the environment on fatty acid profiles to physiologically prepare the larvae to adapt to higher salinity conditions. Linoleic acid (18:2n-6) content was higher in fresh water fish and its reduction during embryo and larval development was accompanied by a significant increase of arachidonic acid (20:4n-6), which was not observed in embryos or larvae from broodstock fish from estuary or aquaculture origin. Both environment and diet of broodstock fish affected lipid and fatty acid composition of G. maculatus embryo and larvae as well as their changes during development.

Atlantic salmon (Salmo salar) were fed 6 experimental diets containing three levels of arachidonic acid (ARA) (0.18 g kg−1, 0.28 g kg−1 and 0.63 g kg−1 for low, medium and high levels, respectively) and two levels of vitamin E (150 and 730 mg kg−1 for low and high levels, respectively). At the end of the experimental period, fatty acids in the liver and immunity markers (lysozyme activity, respiratory burst and phagocytic activity) were determined and fish subjected to a challenge test against the salmonid rickettsial syndrome (SRS) pathogen. ARA, vitamin E or their interaction did not exert an effect on fish performance, whereas ARA alone clearly increased the deposition of ARA. Dietary vitamin E only enhanced liver vitamin E deposition, while the interaction of ARA and vitamin E influenced lysozyme activity and EPA/ARA ratio pointing out the effect of both nutrients on the fish immune system and metabolism. Only the medium concentration contributed to reducing mortality when the fish were exposed to the SRS pathogen. In conclusion, different levels of supplementation with ARA and vitamin E in the diet had no effect on productivity, but did have effects on immune markers and cumulative mortality when fish were exposed to the SRS pathogen.

Despite the importance of certain highly unsaturated fatty acids in osmotic regulation, few studies have been addressed to determine the essential fatty acid requirements for a given species cultured under different salinities. As Galaxias maculatus is a diadromic species, the present study aimed to determine the effect of salinity on the optimum dietary EPA/docosahexaenoic (DHA) ratio for survival and growth during the larval stages. Larvae were fed for 20 days with rotifers containing two different EPA/DHA ratios (low: 0.64 and high: 2.18) at three different salinities (0, 10 and 15 g L−1). The results of this study showed a marked effect of water salinity on larval dietary lipid utilization in G. maculatus larvae. These results suggested that G. maculatus larvae reared at higher salinities may have a higher dietary requirement for DHA, whereas larvae reared at 0‰ showed higher requirements for EPA. The overall results of the present study indicate that even small changes in salinity can determine the optimum dietary EPA/DHA ratio and the quantitative essential fatty requirements of fish. This may have important repercussions and affect the rearing performance of G. maculatus cultured under different salinities.

RESUMEN.Actualmente la tendencia de la acuicultura mundial está orientada hacia la diversificación de los cultivos, principalmente de especies nativas. El congrio colorado Genypterus chilensis es un pez nativo de alta demanda gastronómica y explotación estacional que lo proyecta como candidato para el desarrollo de su tecnología de cultivo. El objetivo de este trabajo fue evaluar la eficiencia de dos sistemas de incubación de masas de huevos de G. chilensis, uno con circuito cerrado de agua (SICC) y el otro con circuito abierto (SICA); su eficiencia fue medida por el porcentaje de eclosión de huevos. Dos ensayos fueron realizados midiendo y comparando los porcentajes de fecundación y eclosión de huevos en cuatro réplicas entre los dos sistemas, encontrándose solo diferencias significativas entre los porcentajes de fecundación del bioensayo 2. El bioensayo 1 tuvo un 81% promedio de fecundación de los huevos y el porcentaje promedio de eclosión para el SICC fue 42,9 ± 34,5% y para el SICA fue 0,0 ± 0,0%. El bioensayo 2 tuvo un porcentaje promedio de fecundación de los huevos de 87,3 ± 2,6% para el SICC y 79,8 ± 3,2% para el SICA y el porcentaje promedio de eclosión para el SICC fue 27,9 ± 33,7% y para el SICA fue 4,8 ± 5,6%. Se discuten los parámetros de incubación para obtener una máxima eclosión y se entrega una proposición para mejorar el sistema SICC. El sistema de incubación con circuito cerrado de agua generó mayores sobrevivencias en los huevos de G. chilensis. Palabras clave: incubación, huevos, congrio colorado, Genypterus chilensis, Chile. Evaluation and comparison of the efficiency of two incubation systemsfor Genypterus chilensis (Guichenot, 1848) eggs ABSTRACT. The current trend in world aquaculture is towards the diversification of cultures, mainly native species. The red cusk eel Genypterus chilensis is a native Chilean species of high gastronomic demand and seasonal exploitation that is projected as a candidate for the development of farming technology. The objective of this study was to test the efficiency of two incubation systems for G. chilensis egg masses, one with a closed water circuit (SICC) and the other with an open water circuit (SICA). Efficiency was measured by the percentage of eggs hatched. Two assays were performed, measuring and comparing the percentages of egg fecundation and hatching in four replicates between the two incubation systems. Significant differences were only found between the percentages of fecundation of bioassay 2. On average, in bioassay 1, egg fecundation reached 81%, and the average of hatching for the SICC was 42.9 ± 34.5% and for the SICA was 0.0 ± 0.0%. Bioassay 2 had an average fecundation of 87.3 ± 2.6% for the SICC and 79.8 ± 3.2% for the SICA, and the average for hatching was 27.9 ± 33.7% for the SICC and 4.8 ± 5.6% for the SICA. Incubation parameters for maximum hatching were discussed and a proposal was made for improving the SICC system. The incubation system with a closed water circuit generated greater survival of G. chilensis eggs.