Goblet cell types in intestine of tiger barb and black tetra (Cyprinidae, Characidae: Teleostei)

Morphology of the digestive system in carnivorous freshwater dourado Salminus brasiliensis

The digestive system of teleost shows remarkable functional and morphological diversity. In this study, the digestive tract and accessory organs of dourado Salminus brasiliensis are characterized using anatomical, histological, histochemical and immunohistochemical analyses. The existence of taste buds bordered by microridges in the oesophagus of dourado was recorded for the first time, thus showing that the species drives food intake by either swallowing or rejecting the food item. The Y-shaped stomach of dourado consisted of cardiac, cecal and pyloric regions with tubular gastric glands registered solely in the cardiac and cecal segments. The intestine is a short N-shaped tube with two loops, an intestinal coefficient of 0.73. The structure of pyloric caeca is similar to that of the intestine wall, comprising tunica mucosa, tela submucosa, tunica muscularis and tunica serosa layers. Histochemical analyses revealed an increased incidence of goblet cells from the midgut to the hindgut segment. A well-developed enteric plexus of scattered nerve cell and fibres are found along the digestive tract, and the calcitonin gene-related peptide (CGRP) immunoreactive neurons and fibres were identified in the myenteric plexus from the oesophagus to the hindgut. The exocrine pancreas appears diffuse in the mesentery around the stomach, intestine and also reaches the liver, and the endocrine pancreas is organized as a few islets of Langerhans. The liver comprises three distinct, asymmetric lobes, and the portal triad arrangement was registered in this tissue.

Transcriptome analysis reveals molecular mechanisms responsive to acute cold stress in the tropical stenothermal fish tiger barb (Puntius tetrazona)

BACKGROUND

Tropical stenothermal fish exhibit special tolerance and response to cold stress. However current knowledge of the molecular mechanisms response to cold stress in aquatic ectotherms is largely drawn from eurythermal or extreme stenothermal species. The tiger barb Puntius tetrazona is a tropical stenothermal fish, with great popularity in aquarium trade and research.

RESULTS

To investigate the response mechanism of P. tetrazona to low temperature, fish were exposed to increasing levels of acute cold stress. Histopathological analysis showed that the brain, gill, liver and muscle tissues appeared serious damage after cold stress (13 °C). Brain, gill, liver and muscle tissues from control (CTRL) groups (27 °C) and COLD stress groups (13 °C) of eight-month fish (gender-neutral) were sampled and assessed for transcriptomic profiling by high-throughput sequencing. 83.0 Gb of raw data were generated, filtered and assembled for de novo transcriptome assembly. According to the transcriptome reference, we obtained 392,878 transcripts and 238,878 unigenes, of which 89.29% of the latter were annotated. There were 23,743 differently expressed genes (DEGs) been filtered from four pairs of tissues (brain, gill, liver and muscle) between these cold stress and control groups. These DEGs were mainly involved in circadian entrainment, circadian rhythm, biosynthesis of steroid and fatty acid. There were 64 shared DEGs between the four pairs of groups, and five were related to ubiquitylation/deubiquitylation. Our results suggested that ubiquitin-mediated protein degradation might be necessary for tropical stenothermal fish coping with acute cold stress. Also, the significant cold-induced expression of heat shock 70 kDa protein (HSP70) and cold-induced RNA-binding protein (CIRBP) was verified. These results suggested that the expression of the molecular chaperones HSP70 and CIRBP in P. tetrazona might play a critical role in coping with acute cold stress.

CONCLUSIONS

This is the first transcriptome analysis of P. tetrazona using RNA-Seq technology. Novel findings about tropical stenothermal fish under cold stress (such as HSP70 and CIRBP genes) are presented here. This study contributes new insights into the molecular mechanisms of tropical stenothermal species response to acute cold stress.

Effects of Graded Dietary Inclusion Level of Full-Fat Hermetia illucens Prepupae Meal in Practical Diets for Rainbow Trout (Oncorhynchus mykiss)

Simple Summary

The sustainability of fish production is mainly driven by the protein source used in aquafeeds. In conventional fish feed, protein sources are mostly vegetable ingredients and fishmeal. The present study explored the potential use of full-fat Hermetia illucens prepupae meal (H) replacing 0% (H0), 25% (H25), and 50% (H50) conventional ingredients in practical diets for rainbow trout. No significant differences in growth were observed in all experimental groups, while in fish fed the H50 diet both hepatic and intestinal alterations were detected. In addition, in the same fish group, genes related to stress and immune-response were significantly up-regulated. The results obtained so far highlighted an overall physiological adaptation of fish to the dietary manipulation, suggesting an adverse effect of full-fat H at the highest inclusion level.

Abstract

This study investigated the effects of dietary inclusion levels of full-fat Hermetia illucens prepupae meal (H) on growth and gastrointestinal integrity in rainbow trout (Oncorhynchus mykiss). A 98-day study was conducted using triplicate groups of trout (initial body weight, 137 ± 10.5 g) kept in 1-m³ tanks in a flow-through well water system. Three dietary treatments were prepared: one based on fishmeal and purified protein-rich vegetable ingredients (H0), and two experimental diets including graded levels of H meal (25% and 50%, referred to as H25 and H50, respectively). At the end of the feeding trial, no differences were observed in growth performance and plasma metabolite levels, with the biometric data confirmed by the liver expression of the genes involved in somatic growth regulation (igf1 and mstn1a). In the H50 group, a three-fold up regulation of liver hsp70 was observed. An activation of the stress/immune response (il-10, tnf-α, and tlr-5) was observed in medium intestine in the H25 and H50 groups (p < 0.05) together with a villi length reduction detected through histological analyses. Liver histology and Fourier Transform Infrared Imaging (FTIRI) spectroscopy highlighted an increase in lipid deposition. These findings suggest that caution should be taken into account when 50% replacement of conventional ingredients with H is selected.

Histochemical and immunohistochemical characterization of rodlet cells in the intestine of two teleosts, Anguilla anguilla and Cyprinus carpio

Rodlet cells (RC) are characterized by a distinctive cell cortex and conspicuous inclusions named "rodlets." These cells are particularly abundant and large in size in intestine of eels. Histochemical, immunohistochemical and ultrastructural investigations were carried out on European eel Anguilla anguilla and Common carp Cyprinus carpio from Northern Italy. Eight biotinylated lectins were used to probe for specific carbohydrate residues in deparaffinized, hydrated intestinal sections of eel and carp. Five antibodies were tested on intestinal sections of both fish species: inducible nitric oxide synthase (i-NOS), leu-enkephalin, lysozyme, serotonin and tumour necrosis factor-α. Lectin histochemistry revealed rodlet cells (RCs) of the eel intestine to react with two of the eight lectins tested, specifically Concanavalin A (ConA) and Sambucus Nigra Agglutinin (SNA). This contrasted to lectin staining of RCs in the intestine of common carp, where four of the eight lectins showed a positive reaction; Dolichos Biflorus Agglutinin (DBA), Wheat Germ Agglutinin (WGA), SNA and ConA. RCs in eel and carp intestine were immunoreactive with antibodies to lysozyme and i-NOS. The occurrence of the inflammatory peptides lysozyme and i-NOS in RCs of the eel and common carp poses in favour that these cells are involved in the mechanism of defence against pathogens.