Characteristics of a gill resection – Regeneration model in freshwater laboratory-reared Atlantic salmon (Salmo salar)

Abstract

Impaired gill function is a critical issue in aquaculture due to factors such as poor water quality, disease, and farm management practices which can greatly compromise gill integrity and ultimately fish growth and survival. Regeneration of damaged gill tissue has been reported for some fish species, however, little is known about Atlantic salmon, which is one of the most economically important salmonid species. This study investigated the regenerative capability of gill tissue following resection in post-smolt Atlantic salmon reared in fresh water. Fish were subjected to two levels of resection severity: 30% or 50% of filament length. Changes in filament length and the cytological and functional capacity of regenerated tissue were studied at several time points post-resection (PR). On average, 38% ± 3.89 of the resected filament length regenerated in both resected groups at week-20 PR. However, absolute regeneration (mm) in 50% resected filaments was greater as compared to the 30% resected filaments. In both groups, regeneration percentage was significantly different among individuals, but was not correlated with initial body size, condition factor, or overall fish growth rate. Immunohistochemistry showed an increase in cell proliferation at the filament tip shortly after resection followed by the appearance of ionocytes, chemoreceptive neuroepithelial cells (NECs), and nerve fibres at week-4 PR. In both resected groups >50% and 90% of NECs were innervated by week-12 and -20 PR, respectively. Gill Na+/K+-ATPase activity in regenerated tissue was not significantly different from that of internal control and non-resected control fish. Our results demonstrate significant regeneration and apparent functional recovery of resected gill filaments in Atlantic salmon which has important implications for recovery from gill damage and developing best practices for maintenance of gill health of farmed salmon.