Green abalone, Haliotis fulgens infected with the agent of withering syndrome do not express disease signs under a temperature regime permissive for red abalone, Haliotis rufescens

Abstract

All California abalone species have been shown to be susceptible to infection with the bacterial agent of abalone withering syndrome (WS), although expression of signs of the disease may vary between species and with environmental conditions. We examined thermal modulation of WS expression in green abalone Haliotis fulgens at temperatures mimicking El Niño (18.0°C) and La Niña (14.2°C) events in southern California. In contrast to results obtained from previous experiments with red abalone, H. rufescens, the higher temperature did not result in higher infection intensities of the causative agent of the disease nor increase in clinical signs of disease. These results demonstrate clear differences in thermal regulation of disease expression between abalone species, and provide further data suggesting that green abalone should be a target species of recovery efforts in southern California, where WS is endemic.

Physiological performance of juvenile Haliotis rufescens and Haliotis discus hannai abalone exposed to the withering syndrome agent

“…Another study (García-Esquivel et al, 2007) indicated that H. fulgens maintained at 25°C do display the signs of WS, whereas temperatures P25°C could cause thermal stress, thereby contributing to physiological deterioration of the organism and therefore vulnerability to WS-RLOs. Contrary to the hypothesis of ''thermal stress to the host'' as a factor triggering WS, Moore et al (2009) proposed that the temperature at which clinical signs of WS are expressed is more closely related to the preferred temperature of each species. The preferred temperature of ectotherms, i.e., that chosen by animals in a temperature gradient, reflects the optimal temperature for many biological processes, such as metabolism, movement, reproduction, and growth (Jobling, 1981).…”

“…increasing its susceptibility to WSRLOs. The specific role of temperature in the expression of WS and other factors that may favor the development of C. X. californiensis remain to be investigated among abalone species (Moore et al, 2009). In the specific case of H. discus hannai, future studies should investigate the conditions (e.g., higher temperatures) under which this species may be susceptible to the development of WS.…”

“…The transmission of WS is direct and horizontal via the oral-fecal route (Moore et al, 2001a). Susceptibility to WS and its expression differ among abalone species and are influenced by the ambient temperature among other factors (Moore et al, 2009). The clinical signs of WS are characterized by morphological changes in the digestive gland, such as metaplasia (cells involved in secretion/absorption are replaced by transport ducts), and/or degeneration of gastrointestinal tissue in the form of atrophy of tubules, increases in connective tissue, and inflammation.…”

Withering syndrome in the abalone Haliotis diversicolor supertexta

“…However, green abalone only showed signs of WS when held at elevated temperatures, e.g. 25°C (Garcia-Esquivel et al 2007), but not when held at 18°C, a temperature at which black and red abalones typically succumb to WS , Moore et al 2009). …”

“…These losses led, in part, to an initial closure of the California black abalone fishery in 1993, followed by total closure in 1997 (Haaker et al 2001). Losses due to WS vary among host species from extremely high losses in white abalone (Friedman et al 2007) to moderate losses in red abalone and low to moderate losses in green and pink abalones (Tinajero et al 2002, Vilchis et al 2005, Moore et al 2009). In Baja California, Mexico, 32.5% of pink and 27% of green abalones examined had clinical signs of WS (Tinajero et al 2002).…”