Gill histopathological responses of Amphilophus citrinellus larvae subjected to different salinities during larviculture

Introduction:

Gills are essential organs in fish, performing functions such as gas exchange, nitrogenous waste excretion, and osmoregulation. Their morphological and functional plasticity in response to environmental variations makes gill histopathology a useful indicator of physiological responses to environmental stress. This study aimed to describe gill histopathological alterations in Amphilophus citrinellus larvae exposed to different salinities during larviculture.

Methods:

Larvae at 5 days of age were reared for 30 days at salinities of 0, 2, 4, 6, 8, and 10 g salt L⁻¹, with four replicates per treatment and 14 larvae per replicate. During the first 15 days, larvae were fed Artemia sp. nauplii and subsequently received a commercial diet containing 450.0 g kg⁻¹ crude protein. At the end of the experiment, gills were collected, histologically processed, and evaluated. Four slides per treatment were selected, with three photomicrographs analyzed per slide. Histopathological alterations were quantified using the histopathological alteration index (HAI), and lesions were classified according to the degree of tissue impairment. Data were analyzed using the Kruskal–Wallis test followed by Dunn's test.

Results:

Larvae maintained at 0 g salt L⁻¹ exhibited normal gill organization, with preserved primary and secondary lamellae and epithelial integrity. At 2 and 4 g salt L⁻¹, edema in the secondary lamellae and mucous cell hyperplasia were observed, indicating an adaptive response. At 6 and 8 g salt L⁻¹, congestion of the central venous sinus was also observed, suggesting vascular impairment. Exposure to 10 g salt L⁻¹ caused structural damage, including disorganization and fusion of secondary lamellae and aneurysm formation.

Conclusion:

Increasing salinity promoted progressive gill histopathological alterations in A. citrinellus, ranging from adaptive responses at low salinities to structural damage under hypersaline conditions, demonstrating the sensitivity of gill tissue to osmotic stress during early development.