Gut Microbiota and Energy Homeostasis in Fish

The microorganisms within the intestinal tract (termed gut microbiota) have been shown to interact with the gut-brain axis, a bidirectional communication system between the gut and the brain mediated by hormonal, immune, and neural signals. Through these interactions, the microbiota might affect behaviors, including feeding behavior, digestive/absorptive processes (e.g., by modulating intestinal motility and the intestinal barrier), metabolism, as well as the immune response, with repercussions on the energy homeostasis and health of the host. To date, research in this field has mostly focused on mammals. Studies on non-mammalian models such as fish may provide novel insights into the specific mechanisms involved in the microbiota-brain-gut axis. This review describes our current knowledge on the possible effects of microbiota on feeding, digestive processes, growth, and energy homeostasis in fish, with emphasis on the influence of brain and gut hormones, environmental factors, and inter-specific differences

The piranha genome provides molecular insight associated to its unique feeding behavior

The piranha enjoys notoriety due to its infamous predatory behavior but much is still not understood about its evolutionary origins and the underlying molecular mechanisms for its unusual feeding biology. We sequenced and assembled the red-bellied piranha (Pygocentrus nattereri) genome to aid future phenotypic and genetic investigations. The assembled draft genome is similar to other related fishes in repeat composition and gene count. Our evaluation of genes under positive selection suggests candidates for adaptations of piranhas’ feeding behavior in neural functions, behavior, and regulation of energy metabolism. In the fasted brain, we find genes differentially expressed that are involved in lipid metabolism and appetite regulation as well as genes that may control the aggression/boldness behavior of hungry piranhas. Our first analysis of the piranha genome offers new insight and resources for the study of piranha biology and for feeding motivation and starvation in other organisms

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

Fish are the most diversified group of vertebrates and, although progress has been made in the past years, only relatively few fish species have been examined to date, with regards to the endocrine regulation of feeding in fish. In fish, as in mammals, feeding behavior is ultimately regulated by central effectors within feeding centers of the brain, which receive and process information from endocrine signals from both brain and peripheral tissues. Although basic endocrine mechanisms regulating feeding appear to be conserved among vertebrates, major physiological differences between fish and mammals and the diversity of fish, in particular in regard to feeding habits, digestive tract anatomy and physiology, suggest the existence of fish- and species-specific regulating mechanisms. This review provides an overview of hormones known to regulate food intake in fish, emphasizing on major hormones and the main fish groups studied to date

Structure Of The Thyroid Gland, Serum Thyroid Hormones, And The Reproductive Cycle Of The Atlantic Stingray, Dasyatis Sabina

This study examines the role of the thyroid gland in the control of reproduction in the viviparous Atlantic stingray, Dasyatis sabina. Thyroid activity in individuals in different reproductive stages was assessed both by microscopic examination of the gland, and by analysis of circulating levels of thyroid hormones from the same individuals. The thyroid gland is a cylindric organ, embedded in a connective tissue capsule, and composed of follicles, i.e., monolayer spheres of thyroid epithelial cells. Stingray follicular cells possess several characteristic features, namely apical cilia and a well-developed endoplasmic reticulum. Cells vary in size and shape, according to the activity of the gland. No structural differences were observed between the thyroid glands of the two sexes. Both thyroid hormones, triiodothyronine, [T3 ], and thyroxine, [T4], were detected in the serum of all animals examined. Levels ranged from 1.3-2.6 μg/100 ml for total T4, and from 1.2-2.6 ng/ml for total T3. The T4 levels did not vary significantly in any group. Immature individuals and females undergoing oogenesis had the lowest levels of circulating T3 and mature females from ovulation throughout gestation had high thyroid gland activity and high levels of circulating T3

Measure of selection operating on <i>Ben4</i> and <i>Ben9</i> genes in <i>D</i>. <i>plexippus</i> and 4 related species.

<p>a) Phylogenetic tree based on the nucleotide sequence alignment of the region shared between <i>Ben4</i> and <i>Ben9</i> in <i>Danaus</i> species samples and CcBV. The values in brackets indicate the number of lepidopteran individuals used in the analysis. b) Plot of the dN/dS value of each codon along the <i>Ben</i> genes based on the alignment of the butterfly sequences. The red bars represent values that are significantly under positive or negative selection (HyPhy, p-value ≤ 0.1). The asterisks identify the sites also under positive selection with the PAML approach. The yellow blocks under the dN/dS graphs represent the <i>Ben</i> gene structure composed of three exons. The first exon corresponds to a PHA02737 domain and the BEN domain (represented in purple) is encoded by the end of the third exon. Note that the truncated <i>Ben4</i> gene conserved in <i>D</i>. <i>plexippus</i> corresponds to the third exon of CcBV <i>Ben4</i> gene, which contains the BEN domain.</p