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Abalone: Gastropod Species In South African Aquaculture

2117 words - 9 pages

Abalone (Haliotis midae) is one of the important commercially farmed gastropod species in South African aquaculture (Britz 1995) and it is farmed in intensive land-based, pump ashore, flow-through facilities (Yearsley 2008). The development of the industry has been stimulated by research and development and by a good market demand for abalone both live and processed (Sales and Britz 2001). In abalone farming, the increase in disease outbreaks and their effect on production result in a regular risk in commercial aquaculture sectors (Mialhe et al. 1995). In Taiwan, outbreaks of abalone herpesvirus (AbHV) resulted in high mortalities of farmed abalone Haliotis diversicolor supertexta (Chang et ...view middle of the document...

2001). Consequently, excessive or incorrect antimicrobial use can lead to the emergence of bacterial resistance (Verschuere et al. 2000). Efficacy of antimicrobial use to prevent diseases has raised many questions, as a lot of research has been conducted in the development of antimicrobial inhibition of pathogens (Nomoto 2005). However, “the use of antibiotics in aquaculture also constitutes a threat to human health and to the environment” (Alderman and Hastings 1998; Cabello 2006). In addition, residues of antibiotics in aquaculture products can lead to human health problems and can exacerbate problems of allergy and toxicity by altering gut microflora (Cabello 2006).
Although disease control is an aspect of intensive animal production, controlling disease in the aquatic environment is further complicated by the relationship between pathogens and their host and the frequent use of open production systems (Olafsen 2001) that discharge effluent directly into the environment. In many cases, bacteria of the genus Vibrio are opportunists, causing disease when the host organism’s immune system is suppressed or physiologically stressed, with the frequency of infection often being attributable to environmental conditions (Alderman and Hastings 1998).
Stress has been defined by Barton (1997) as the “response of an organism to any demand placed on it such that it causes an extension of a physiological state beyond its normal resting state to the point that the chances of survival may be reduced”. Several studies have demonstrated that stress response alters disease resistance and survival in abalone (Elston and Lockwood 1983; Wells and Baldwin 2000). In a culture environment, abalone are constantly subjected to a wide range of stressors which include repeated mechanical disturbances such as sorting, grading and transport. There is a relationship between the magnitude of the stress response and disease, which has been associated with disease outbreaks in abalone and in many other animals (Hooper et al. 2007). In abalone the stress response and decreased immune function capacity can lead to bacterial infections and mortality (Cheng et al. 2004a). However, this link is based on immune function tests carried out after applying stressors such as salinity fluctuations, handling through shaking, decreased dissolved oxygen concentration, increased concentration of ammonia and increased temperature (Hooper et al. 2007).
Aquaculture husbandry processes induce physiological stress which can inhibit growth in farmed animals by suppressing appetite and feed intake (Schreck et al. 1997; McCormick et al. 1998) and also by means of a stress restraint effect on the excretion and the activities of growth hormones and insulin-like growth factor I (Pickering 1993; Pankhurst and van Der Kraak 1997; Dyer et al. 2004). In order to mitigate the mortality associated with infectious diseases in farmed abalone, a better understanding of the abalone’s response to bacterial or...

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