Streptococcus iniae infections in Red Sea cage-cultured and wild fishes

Abstract

Streptococcus iniae was isolated from 2 moribund wild Red Sea fishes, Pomadasys stridens (Pomadasyidae) and Synodus variegatus (Synodontidae), both collected in shallow waters along the Israeli coast of the Gulf of Eilat. The site is approximately 2 km from a mariculture cage farm in which streptococcal infections were diagnosed in previous years in the red drum Sciaenops ocellatus. This is the first report of S. iniae in Red Sea fishes. Biochemical and molecular similarities between the isolates from cultured fishes and those from the wild specimens suggest that a single strain is involved, and that 'amplification' and dispersal of this pathogen from captive to feral fishes have occurred. At the molecular level, the pathogen is different from the S. iniae isolates that have been afflicting the Israeli freshwater aquaculture in recent years. Although S. iniae prevalence in the wild fish populations of the area remains to be determined, the northernmost region of the Gulf of Eilat, virtually landlocked and with generally calm seas and weak currents, seems to be particularly vulnerable to the impact of diseases that develop in this mariculture system. KEY WORDS: Fish disease · Mariculture · Red drum · Sciaenops ocellatus · Sea bass · Dicentrarchus labrax · Tilapia · Oreochromis mossambicus · 16S rRNA · PCR Resale or republication not permitted without written consent of the publisherDis Aquat Org 49: [165][166][167][168][169][170] 2002 populations increases the opportunity for disease transmission in both directions, since translocated species may not only be extremely sensitive to a local pathogen but may themselves carry exotic diseases that can spread to indigenous wild populations (Paperna 1998).In the Eilat region, streptococcosis has recurred repeatedly since it was first diagnosed in 1996 in the red drum (see Table 1). During the summer of 2000, persistent mortalities of wild fishes in the shallow waters of Eilat's northern coast were investigated. Gram-positive cocci in chains were isolated from 2 moribund wild specimens and compared with streptococcal isolates from fishes cultured in this region in previous years. MATERIALS AND METHODS Fishes.The infection chronology, sources of isolation and list of fish hosts are summarized in Table 1. The first case was diagnosed in 1995 in a stock of European sea bass Dicentrarchus labrax submitted to our laboratory for examination from a fish farm in Ashdod, on the Mediterranean coast of Israel. All subsequent cases refer to fish grown in the Eilat area (Red Sea). Water in this region is subjected to limited seasonal fluctuations of temperature (23 ± 1.5°C) and salinity (40 ± 1 ‰). Red drum Sciaenops ocellatus were examined during mortality outbreaks in the cages. The tilapia Oreochromis mossambicus, adapted to seawater, were maintained at Israel Oceanographic and Limnological Research National Center for Mariculture in the facilities of the Reproduction Department for experimental purposes. The lined piggy Pomadasys stridens (Pomadasyidae) and the lizar...

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