Influence of Age on Stress Responses of White Seabream to Amyloodiniosis

Abstract

Amyloodiniosis is a disease that represents a major bottleneck for semi-intensive aquaculture, especially in Southern Europe. The inefficacy of many of the treatments for this disease on marine fish produced in semi-intensive aquaculture has led to a new welfare approach to amyloodiniosis. There is already some knowledge of several welfare issues that lead to amyloodiniosis as well as the stress, physiological, and immunological responses to the parasite by the host, but no work is available about the influence of fish age on the progression of amyloodiniosis. The objective of this work was to determine if stress, hematological, and histopathological responses are age dependent. For that purpose, we determined the mortality rate, histopathological lesions, hematological indexes, and stress responses (cortisol, glucose, lactate, and total protein) in “Small” (total weight: 50 ± 5.1 g, age: 273 days after eclosion (DAE)) and “Big” (total weight: 101.3 ± 10.4 g, age: 571 DAE) white seabream (Diplodus sargus) subjected to an Amyloodinium ocellatum infestation (8000 dinospores mL−1) during a 24-h period. The results demonstrated a strong stress response to A. ocellatum, with marked differences in histopathological alterations, glucose levels, and some hematological indexes between the fish of the two treatments. This work elucidates the need to take in account the size and age of the fish in the development and establishment of adequate mitigating measures and treatment protocols for amyloodiniosis.

Cytotoxic and Hemolytic Activities of Extracts of the Fish Parasite Dinoflagellate Amyloodinium ocellatum

“…Two 600 L rectangular fibreglass tanks filled with UV sterilized seawater were infested with 5000–6000 A. ocellatum tomonts collected from an induced outbreak according to the methodology described in [ 20 , 21 ]. Several naive and unparasitized gilthead seabreams juveniles were exposed to the parasite to increase the dinospore infective population of the tank and to maximize trophont and tomont production per day, as described in [ 19 ].…”

“…Diseased fish display lethargic and sluggish movements, and slow opercular movement when heavily parasitized [ 13 , 16 ]. Changes in several blood and physiological parameters were also observed in the first 24 h of A. ocellatum infestation, prior to major changes in the gill histopathology of gilthead seabream ( Sparus aurata ) or the white seabream ( Diplodus sargus ) [ 19 , 20 , 21 ]. These changes have also been observed in heavily parasitized fish from other farmed species, such as the yellowtail ( Seriola dorsalis ) [ 22 ].…”

Establishment of a gill cell line from yellowfin seabream (Acanthopagrus latus) for studying Amyloodinium ocellatum infection of fish

“…Amyloodiniosis is a ‘quiet’ disease; the host displays no clinical symptoms following infection of a small number of trophonts, but due to the rapid proliferation of A. ocellatum , the fish do not respond to therapy by the time of fish showing signs of disease as it is already too late (Soares et al., 2011). Several studies that investigated the effects of A. ocellatum infection on the host linked fish mortality to inflammation, osmoregulatory disturbances and secondary microbial infections due to severe epithelial damage (Massimo et al., 2022; Moreira et al., 2017, 2018, 2019). Histopathological examination of infected fish gills revealed epithelial cell hyperplasia and hypertrophy of the lamellae, as well as fusion of secondary lamellae, telangiectasia and mucous cell proliferation, culminating in disintegration and necrosis of the lamellar structure of the gill (Noga, 2012; Nozzi et al., 2016).…”

“…Amyloodiniosis is a 'quiet' disease; the host displays no clinical symptoms following infection of a small number of trophonts, but due to the rapid proliferation of A. ocellatum, the fish do not respond to therapy by the time of fish showing signs of disease as it is already too late (Soares et al, 2011). Several studies that investigated the effects of A. ocellatum infection on the host linked fish mortality to inflammation, osmoregulatory disturbances and secondary microbial infections due to severe epithelial damage (Massimo et al, 2022;Moreira et al, 2017Moreira et al, , 2018Moreira et al, , 2019.…”

Welfare of Fish—No Longer the Elephant in the Room

“…The study by Moreira et al [7] takes an ontogenic approach into amyloodiniosis, a well-known health problem in white seabream (Diplodus sargus) farmed in Southern Europe. Focusing on fish health is not new in welfare research.…”