A Summer Mortality Outbreak of Lactococcosis by Lactococcus garvieae in a Raceway System Affecting Farmed Rainbow Trout (Oncorhynchus mykiss) and Brook Trout (Salvelinus fontinalis)

Abstract

Lactococcosis is a fish disease of major concern in Mediterranean countries caused by Lactococcus garvieae. The most susceptible species is the rainbow trout (Oncorhynchus mykiss), suffering acute disease associated with elevated mortalities compared to other fish species. References reported that other salmonids are also susceptible to the disease, but no mortality outbreak has been described to date. The aim of this study was to present a mortality outbreak that occurred in brook trout (Salvelinus fontinalis) farmed in northwestern Italy during the summer of 2018. Fish exhibited clinical signs, such as exophthalmos, diffused hemorrhages localized in the ocular zone, hemorrhagic enteritis, and enlarged spleen. L. garvieae was isolated in all fish. Molecular and epidemiological characterization of the isolates, through Pulsed Field Gel Electrophoresis (PFGE), confirmed the initial hypothesis of water as vehicle of infection favoring transmission between rainbow trout farmed in upstream compartments and brook trout located in downstream tanks. Moreover, several environmental conditions affected and promoted the outbreak, among them the high-water temperature, which probably induced a physiological stress in brook trout, being way above the optimal temperature for this species, increasing the susceptibility to infection.

Detection and virulence of Lactococcus garvieae and L. petauri from four lakes in southern California

“…The presence of salmonids in the sampled lakes is suspected, as three of the lakes (Jess Ranch, Spring Valley, and Horseshoe lakes) are stocked yearly by private and state programs in the winter (CDFW, https://wildl ife.ca.gov/ Fishi ng/Hatch eries); however, the salmonid population is known to fluctuate seasonally, and many fish do not survive, particularly during the warmer months. Since this disease is known to have a direct association with environmental temperatures greater than 15°C, the time of year at which surveillance studies are conducted may be critical (Eyngor et al 2004;Soltani et al 2008;Pastorino et al 2019).…”

“…Direct and indirect horizontal transmission routes have been hypothesized for L. garvieae (Vela et al 2000; Vendrell et al 2006; Pastorino et al 2019). Besides transmission by clinically and subclinically infected fish hosts, transmission through contaminated water, soil, and sand or through fecal contamination of environments by piscivorous birds has been proposed (Vendrell et al 2006; Algöet et al 2009; Eraclio et al 2019; Shahin et al 2022).…”

NGS analysis revealed that Lactococcus garvieae Lg‐Per was Lactococcus petauri in Türkiye

“…In subsequent years, L. garvieae spread over the nation (Balta & Dengiz Balta, 2019; Cagirgan, 2004; Ture & Boran, 2015; Türe & Savaş, 2010). Severe mortalities have been notably noticed in the salmonid farms, especially at water temperatures over 15°C, and up to 50%–80% of mortality rates have been reported (Gibello et al, 2016; Pastorino et al, 2019).…”

Lactococcus garvieae isolated from Lake Kariba (Zambia) has low invasive potential in Nile tilapia (Oreochromis niloticus)

“…It affects rainbow trout (Eldar and Ghittino, 1999; Ravelo et al., 2001), Tilapia (Evans et al., 2009; Vendrell et al., 2006), yellow tail (Zlotkin et al., 1998) and several other fish species. In rainbow trout, it is a source of great economic losses especially in the Mediterranean region (Pastorino et al., 2019).…”