Susceptibility and Tolerance of Spotted Seatrout, Cynoscion nebulosus, and Red Snapper, Lutjanus campechanus, to Experimental Infections with Amyloodinium ocellatum

Abstract

Amyloodinium ocellatum is a parasitic dinoflagellate that infects warm-water marine and estuarine fishes and causes mortalities in aquaculture. Its life cycle consists of 3 stages: a feeding trophont that parasitizes the gills and skin where it interferes with gas exchange, osmoregulation, and tissue integrity; a detached reproductive tomont; and a free-swimming infective dinospore. We compared the susceptibility and tolerance of juvenile spotted seatrout, Cynoscion nebulosus, and red snapper, Lutjanus campechanus, to this parasite by individually exposing fish in 3-L aquaria (at 25 C and 33 practical salinity units) to several dinospore doses over different time periods and quantified the size and number of resulting trophonts. We estimated the trophont detachment rate and trophont size at detachment, the 24-hr dinospore infection rate, the dinospore 48-hr median lethal dose (LD(50)), and the trophont lethal load at the 48-hr LD(50). There were no significant differences in dinospore infection rates or dinospore lethal doses between spotted seatrout and red snapper; however, trophonts remained attached longer and attained a larger size in red snapper than in spotted seatrout. The trophont lethal load was significantly higher in spotted seatrout than in red snapper. A proposed model simulating the trophont dynamics reflected our experimental findings and showed that A. ocellatum reproductive success is linked both to the number of dinospores and the size of the trophont, factors that, in turn, are linked to the time the trophont spends on the host and the number of trophonts the host can tolerate.

Amyloodiniosis in aquaculture: A review

“…However, it is best to observe trophonts in their diagnostic attachment to the epithelium in the gill tissue, by ablation of the totality or part of the first two gill arches. 24,38,44,120,159 The necessity of early detection and welfare issues lead also to the development of other tools for the detection of A. ocellatum in the tank environment, mainly with the help of genetic tools. 121…”

“…The feeding stage (trophont) of A. ocellatum, commonly attached to skin, fins, eyes, and gills, can interfere with gas exchange, osmoregulation, and tissue integrity thus resulting in spasmodic gasping, uncoordinated movements, and extensive mortalities of fish. 44 Most recently, Moreira et al 165 described that A. ocellatum dinospores and trophonts produce tissue-specific toxic compounds that may have a role in the attachment and feeding process of this parasite, opening an entirely new area on the parasite-host interaction.…”

“…We can also produce parasites via an uncontrolled methodology to produce tomonts, dinospores, and trophonts, 44,153,161 which produces good but very variable quantities of parasites. This is due to the difficulties in maintaining a stable and controlled number of A. ocellatum in the tanks that gives time to the fish to be infested and shed tomonts to the system that will allow the maintenance of the dinospore population.…”

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“…The only reference of amyloodiniosis in sparids from Persian Gulf was that one reported by Tareen (1986) during a parasitology study on Acanthopagrus cuvieri. Occurrence of amyloodiniosis was recorded by Masson et al (2011) in red snapper (Lutjanus campechanus) in USA and by Ramesh Kumar et al (2015) in silver pompano (Trachinotus blochii) in India. Saraiva et al (2011) reported massive infestation of A. ocellatum in Portuguese marine fish farms causing high mortalities in seabass, seabream and turbot.…”

“…According to a cosmopolitan distribution, this pathogen is capable of living and reproducing in different ecological habitats (temperature ranges: 16 to 30°C and salinity ranges: 10 to 60) and infesting both feral and cultured fish (Paperna, 1984). A. ocellatum causing severe morbidity and mortality in various aquaculture facilities, with attaching to gill and skin of cultured fishes and usually with rapid spread within a few days (Masson, Blaylock, & Lotz, 2011).…”