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ARS Home » Southeast Area » Auburn, Alabama » Aquatic Animal Health Research » Research » Publications at this Location » Publication #233109
Title: Pathogenicity of Streptococcus ictaluri to Channel Catfish

Author
item Pasnik, David
item Evans, Joyce
item Klesius, Phillip
item Shoemaker, Craig
item Yeh, Hung-Yueh

Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2009
Publication Date: 9/1/2009
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H., Shoemaker, C.A., Yeh, H. 2009. Pathogenicity of Streptococcus ictaluri to Channel Catfish. Journal of Aquatic Animal Health. Vol 21 no. 3. 184-188.

Interpretive Summary: Though streptococcal pathogens affect a wide variety of saltwater and freshwater fish, there are few reports of Streptococcus spp. infecting channel catfish (Ictalurus punctatus). The natural infection of channel catfish broodstock with a novel streptococcal species, subsequently named S. ictaluri has recently been reported. Clinical signs with broodstock natural infections included: low-grade mortalities, emaciation, arched backs, gross lesions of the fins and jaws, and diminished reproduction. Catfish were experimentally injected 50 to 75 g channel catfish with S. ictaluri and re-isolated bacteria from jaw and fin lesions. However, no mortalities were reported. Given that mortalities have been reported in broodstock (approximately 2-3 kg) fish and only clinical signs were observed with experimentally infected juvenile (50-75 g) fish, this study examined whether morbidity and mortality could be produced by experimental infection of fry (0.5 g), fingerling (15 g), and juvenile (55 g) channel catfish. Channel catfish exposed by immersion were exposed to baths containing 1012, 1011, 1010, 109, or 108 colony-forming units (cfu) S. ictaluri. Catfish exposed by injection were injected intraperitoneally with 108, 107, 106, 105, or 104 cfu S. ictaluri. The results of this study demonstrated that S. ictaluri could infect fry, fingerling, and young juvenile channel catfish within 21 d post-infection. The overall cumulative percent mortalities (CPM) were 11% for fry and 0% for fingerlings by bath immersion. The CPM was 14% for fingerling and 6% for juvenile catfish by injection. Isolation of S. ictaluri from moribund and dead catfish was confirmed by comparison with a newly-established BIOLOG profile (MicroLog3TM system, BIOLOG Inc., Hayward, California, USA), helping to differentiate the isolates from other Streptococcus spp. These results indicate that channel catfish were only susceptible to high concentrations of S. ictaluri and that older channel catfish were less susceptible, possibly explaining why little mortality has been attributed to S. ictaluri infection in catfish aquaculture.

Technical Abstract: The infectivity of a Streptococcus ictaluri isolate for fry (0.5 g), fingerling (15 g), and juvenile (55 g) channel catfish (Ictalurus punctatus) was determined by bath immersion and injection infectivity experiments. Channel catfish exposed by immersion were exposed to baths containing 1012, 1011, 1010, 109, or 108 colony-forming units (cfu) S. ictaluri. Catfish exposed by injection were injected intraperitoneally with 108, 107, 106, 105, or 104 cfu S. ictaluri. The results of this study demonstrated that S. ictaluri could infect fry, fingerling, and young juvenile channel catfish within 21 d post-infection. The overall cumulative percent mortalities (CPM) were 11% for fry and 0% for fingerlings by bath immersion. The CPM was 14% for fingerling and 6% for juvenile catfish by injection. Isolation of S. ictaluri from moribund and dead catfish was confirmed by comparison with a newly-established BIOLOG profile (MicroLog3TM system, BIOLOG Inc., Hayward, California, USA), helping to differentiate the isolates from other Streptococcus spp. These results indicate that channel catfish were only susceptible to high concentrations of S. ictaluri and that older channel catfish were less susceptible, possibly explaining why little mortality has been attributed to S. ictaluri infection in catfish aquaculture.