Investigation of gill mucus cells of Lake Van fish (Alburnus tarichi) during reproductive migration

Transport stress induces innate immunity responses through TLR and NLR signaling pathways and increases mucus cell number in gills of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂)

Transport stress poses a threat to most teleost fish in production, causing mass losses to the aquaculture industry. Fish gills are a mucosa-associated lymphoid tissue in direct contact with water, and they represent an ideal tissue type to study mechanisms of transport stress. In this study, hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) were exposed to simulated transport stress for 16 h and then allowed to recover for 96 h. Gill tissues and blood samples were collected at 0 h, 2 h, 4 h, 8 h, and 16 h of transport stress and after 96 h of recovery, as well as from fish in a control group at the same sampling times. The activities of alkaline phosphatase, acid phosphatase, and superoxide dismutase and the total antioxidant capacity first increased and then decreased during the 16 h transport treatment. Exposure to 16 h of transport stress resulted in decreased serum triglyceride and total cholesterol contents, increased serum glucose content, increased activities of alanine aminotransferase and aspartate transaminase, and more mucus cells, compared with the control group. Transcriptome analysis revealed differential expression of 1525 genes (803 down-regulated and 722 up-regulated) between the control and 16 h transportation groups. Functional analyses revealed that the differentially expressed genes were enriched in immune response, signal transduction, and energy metabolism pathways. We found that tlr5, tnfɑ, hsp90ɑ, il-1ß, map2k4, il12ba were clearly up-regulated and arrdc2, syngr1a were clearly down-regulated following 8 h and/or 16 h simulated transport after qRT-PCR validation. These findings suggested that Toll- and NOD-like receptor signaling pathways potentially mediate transport stress. Transport stress altered innate immunity responses and energy use in the gill tissues of hybrid yellow catfish. After 96 h of recovery, only alanine aminotransferase and alkaline phosphatase activities and the number of mucus cells had returned to control levels. We speculate that for juvenile yellow catfish to recover to a normal state, a recovery period of more than 96 h is required after 16 h of transportation. These results provide new perspectives on the immune response of yellow catfish under transport stress and theoretical support for future optimization of their transportation.

Histological Study of Suprabranchial Chamber Membranes in Anabantoidei and Clariidae Fishes

Simple Summary

Air-breathing fish constitute a broad evolutionary group of fish, which are generally characterized by distinctive phenotypical plasticity. These fishes usually inhabit waters where oxygen deficiency occurs periodically, which is why they have developed a variety of accessory respiratory organs (AROs) that may be used in an obligatory or a facultative manner. Knowledge of the structure of these organs is important for both the breeding and the conservation of these fish species. The aim of this study was to conduct a comparative histological analysis of two types of AROs found in the Anabantoidei suborder and the Clariidae family, both of which are freshwater fish taxa of high ecological and commercial importance.

Abstract

Accessory respiratory organs (AROs) are a group of anatomical structures found in fish, which support the gills and skin in the process of oxygen uptake. AROs are found in many fish taxa and differ significantly, but in the suborder Anabantoidei, which has a labyrinth organ (LO), and the family Clariidae, which has a dendritic organ (DO), these structures are found in the suprabranchial cavity (SBC). In this study, the SBC walls, AROs, and gills were studied in anabantoid (Betta splendens, Ctenopoma acutirostre, Helostoma temminckii) and clariid (Clarias angolensis, Clarias batrachus) fishes. The histological structure of the investigated organs was partially similar, especially in relation to their connective tissue core; however, there were noticeable differences in the epithelial layer. There were no significant species-specific differences in the structure of the AROs within the two taxa, but the SBC walls had diversified structures, depending on the observed location. The observed differences between species suggest that the remarkable physiological and morphological plasticity of the five investigated species can be associated with structural variety within their AROs. Furthermore, based on the observed histology of the SBC walls, it is reasonable to conclude that this structure participates in the process of gas exchange, not only in clariid fish but also in anabantoids.