Feed intake and gene expression of appetite-regulating hormones in Salminus brasiliensis fed diets containing soy protein concentrate.

Dourado (Salminus brasiliensis) is a large carnivorous fish with high commercial value for which sustainable aquaculture relies on the substitution of expensive dietary animal protein sources in aquafeeds, in particular fish meal (FM), by cheaper plant protein, such as soy protein concentrate (SPC). This study aimed at evaluating feed intake and gene expression of appetite- regulating hormones [orexin, cocaine and amphetamine regulated transcript (CART), leptin, cholecystokinin (CCK) and peptide YY (PYY)] in the intestine, pyloric caeca and hypothalamus of juvenile dourado fed diets containing graded levels of SPC and FM as dietary protein sources for a period of three weeks. Increasing dietary plant protein contents reduced daily feed consumption and the expressions of the anorexigenic hormone CCK in the anterior intestine and in pyloric caeca and PYY in pyloric caeca. No changes were detected in the hypothalamic expression of appetite-regulating hormones, suggesting that gastrointestinal hormones are more involved in the decrease in feeding induced by plant protein diets than central appetite-regulating systems.

Oral administration of antibiotics increased the potential mobility of bacterial resistance genes in the gut of the fish Piaractus mesopotamicus.

BACKGROUND: Aquaculture is on the rise worldwide, and the use of antibiotics is fostering higher production intensity. However, recent findings suggest that the use of antibiotics comes at the price of increased antibiotic resistance. Yet, the effect of the oral administration of antibiotics on the mobility of microbial resistance genes in the fish gut is not well understood. In the present study, Piaractus mesopotamicus was used as a model to evaluate the effect of the antimicrobial florfenicol on the diversity of the gut microbiome as well as antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) using a metagenomic approach. RESULTS: The total relative abundance of ARGs and MGEs significantly increased during the antibiotic exposure. Additionally, phage integrases, transposases, and transposons flanking ARGs accumulated in the gut microbiome of P. mesopotamicus because of the antibiotic exposure. MGEs co-occurring with ARGs showed a significant positive correlation with the total ARGs found. Furthermore, shifts in the gut microbiome towards well-known putative pathogens such as Salmonella, Plesiomonas, and Citrobacter were observed following florfenicol treatment. Mainly Plesiomonas and Citrobacter harbored genes that code for multidrug and phenicol efflux pumps. Moreover, several genes related to RNA processing and modification, cell motility, SOS response, and extracellular structure were enriched due to the antibiotic application. The observed effects were visible during the complete application phase and disappeared at the post-exposure phase. CONCLUSIONS: Our findings suggest that the oral administration of antibiotics increases the potential for MGE-mediated exchange of ARGs in the gut of fish and could contribute to the enrichment and dispersion of ARGs in aquaculture systems. Importantly, this increase in the potential for ARGs exchange could be an effect of changes in community structure and/or ARG mobilization.

Assessment of elimination profile of albendazole residues in fish.

Few drugs are specifically regulated for aquaculture. Thus this study considered albendazole (ABZ) as a potential drug for use in fish, which, however, is not yet regulated for this application. ABZ is a broad-spectrum anthelmintic approved for farmed ruminants and recently considered for treatment of fish parasites. It is the subject of careful monitoring because of potential residues in animal products. This study evaluated the depletion of ABZ and its main known metabolites: albendazole sulfoxide - ABZSO, albendazole sulfone - ABZSO2 and albendazole amino sulfone - ABZ-2-NH2SO2, in the fillets of the Neotropical Characin pacu, Piaractus mesopotamicus, which were fed diets containing 10 mg ABZ kg-1 body weight in a single dose. Fish were euthanised at 8, 12, 24, 48, 72, 96 and 120 hours after medication and the depletion profiles of ABZ, each metabolite and the sum of all marker residues were assessed and evaluated taking into account methodological variations regarding determination of the maximum residue limits adopted by different international regulating agencies for estimation of the withdrawal period (WP). The estimated WPs ranged from 2 to 7 days.

Appetite regulating factors in pacu (Piaractus mesopotamicus): Tissue distribution and effects of food quantity and quality on gene expression.

The pacu Piaractus mesopotamicus is an omnivorous fish considered a promising species for aquaculture. Little is known about the endocrine regulation of feeding in this species. In this study, transcripts for orexin, cocaine and amphetamine regulated transcript (CART), cholecystokinin (CCK) and leptin were isolated in pacu. Orexin, CCK and leptin have widespread mRNA distributions in brain and periphery, CART is limited to the brain. To examine the role of these peptides in the regulation of feeding and energy status, mRNA expression levels were compared between fed and fasted fish and around feeding time. Both orexin and CART brain expressions were affected by fasting and displayed periprandial changes, suggesting a role in both short- and long-term regulation of feeding. CCK intestinal expression decreased in fasted fish and displayed periprandial changes, suggesting CCK acts as a peripheral satiety factor. Leptin was not affected by fasting but displayed periprandial changes, suggesting a role as a short-term regulator. To examine if these peptides are affected by diet, brain and gut expressions were assessed in fish fed with different diets containing soy protein concentrate. Food intake, weight gain and expressions of orexin, CART, CCK and leptin were little affected by replacement of fish protein with soy protein, suggesting that pacu is able to tolerate and grow well with a diet rich in plant material. Overall, our results suggest that orexin, CART, CCK and leptin are involved in the physiology of feeding of pacu and that their expressions are little affected by plant-based diets.

Appetite regulating factors in dourado, Salminus brasiliensis: cDNA cloning and effects of fasting and feeding on gene expression.

The dourado, Salminus brasiliensis (Cuvier, 1816) is a freshwater piscivorous Characin native to South American rivers. Owing to the high quality of its flesh and its fast growth, it is the object of both capture fisheries and fish farming. However, very little is known about the endocrine regulation of feeding and metabolism of dourado. In this study, cDNAs for orexin, CART and CCK were isolated in dourado, and their mRNA tissue distributions examined. In order to assess the role of these peptides in the regulation of feeding of dourado, the effects of fasting and feeding on mRNA expression levels of orexin, CART and CCK in the brain as well as CCK in the intestine were assessed. Whereas orexin and CCK have widespread mRNA distributions in the brain and peripheral organs, CART seems to be mostly limited to the brain. Orexin brain expression increased with fasting and displayed periprandial changes, suggesting it is involved in both long- and short-term regulation of feeding and appetite. CART and CCK hypothalamic expressions were not affected by fasting, but displayed periprandial changes with post-feeding decreases, suggesting roles in short-term satiation. CCK expression in the anterior intestine was not affected by fasting and did not display periprandial changes. Overall, our results suggest that orexin, CART and CCK are involved in the physiology of feeding of dourado.

Fish silage in black bass (Micropterus Salmoides) feed as an alternative to fish meal

The objective of this study was to use the residues of fermented sardine to elaborate the acid fish silage and its use in feed for aquaculture. Biological assay was performed by feeding largemouth bass (Micropterus salmoides) fingerlings (initial weight 22g), with extruded diets (41 percent crude protein; 3,600 kcal/kg digestible energy) containing 0.0, 7.5, 10.0, 12.5, or 15.0 percent of fish silage in partial substitution to the fish meal. The feed conversion ratio and weight gain for the treatments were: 1.26 and 15.76g; 1.11 and 17.07g; 1.19 and 17.81g; 1.18 and 19.83g; 1.47 and 14.64g, respectively. No significant differences (P<0.05) were detected among the treatments. Results indicated that it was possible to use up to 15 percent of acid fish silage as partial substitute for fish meal in the formulation of carnivorous fish feed.

O objetivo desta pesquisa foi estudar a utilização de resíduos de sardinha fermentada para elaboração de silagem química e sua utilização em rações para aquacultura. Foi realizado ensaio de ganho de peso utilizando juvenis de "black bass" (Micropterus salmoides), com peso inicial de 22 gramas, onde utilizou-se rações extrusadas (41 por cento de proteína bruta, 3.600 kcal/kg de energia digestível) contendo 0,0; 7,5; 10,0; 12,5; 15,0 por cento de silagem em substituição à farinha de peixe. A composição química da silagem de pescado (matéria seca) apresentou valores de proteína bruta de 28,47 g 100g-1; lipídeo 8,24 g 100g-1; cinza 60,68 g 100g-1 A conversão alimentar e o ganho de peso para os tratamentos foram, respectivamente: 1,26 e 15,76g; 1,11 e 17,07g; 1,19 e 17,81g; 1,18 e 19,83g; 1,47 e 14,64g. Nenhuma diferença significativa (P<0,05) foi encontrada entre os tratamentos. Os resultados indicam a possibilidade da utilização de até 15 por cento de silagem na substituição da farinha de peixe, em rações para peixes carnívoros.