Submitted to: Aquaculture Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2006
Publication Date: February 26, 2007
Citation: Evans, J.J., Klesius, P.H., Pasnik, D.J., Shoemaker, C.A. 2007. Concurrent experimental streptococcus spp. infections and natural parasitism in channel catfish ictalurus punctatus. Aquaculture Conference Proceedings. Aquaculture 2007. February 26 - March 2, 2007 San Antonio , Texas. p. 282. Technical Abstract: Streptococcus iniae and S. agalactiae are usually not considered pathogens of channel catfish, Ictalurus punctatus, though concurrent infections may decrease catfish survival when infected with streptococcal organisms. Non-parasitized or naturally-parasitized channel catfish fry were challenged with either S. iniae or S. agalactiae to determine whether the streptococcal organisms could cause decreased survival in non-parasitized or concurrently-parasitized catfish. Fish were immersion-challenged with 109, 108, 107, 106, or 105 CFU S. iniae or S. agalactiae/mL in 50 mL water baths and observed for behavior changes, morbidity, and mortality for 7 d after challenge. Cumulative percent survival was high (Table 1; 88 to 100%) among non-parasitized catfish, irrespective of challenge species or dose. Cumulative percent survival decreased (23 to 73%) in Trichodina sp.-parasitized and streptococcal challenged fish. Mortalities among parasitized fish began within 1 d after streptococcal challenge and most occurred within 3 d after experimental challenge. The LD50 values in these Trichodina sp.-parasitized fish 7 d after streptococcal challenge were 1.10 x 107 CFU/mL for S. iniae and 3.80 x 107 CFU/mL for S. agalactiae. The results of the present study indicate that both S. iniae and S. agalactiae alone are not usual pathogens of channel catfish fry. However, these streptococcal organisms can cause decreased survival in young channel catfish externally parasitized with Trichodina sp. Table 1. Cumulative percent survival among channel catfish fry with or without Trichodina sp. infection 7 d after immersion challenge with Streptococcus iniae or S. agalactiae.1 Group(cfu/mL) Cumulative Percent Survival Without Streptococcus iniae Without Streptococcus agalactiae Without Trichodina sp. With Trichodina sp. P value Without Trichodina sp. With Trichodina sp. P value TSB 100a 14b* 0.0001 100a 77a* 0.0126 Group(cfu/mL) Cumulative Percent Survival With Streptococcus iniae With Streptococcus agalactiae Without Trichodina sp. With Trichodina sp. P value Without Trichodina sp. With Trichodina sp. P value 105 100a 73a* 0.0057 100a 59a* 0.0004 106 100a 64a* 0.0010 88b 50a* 0.0027 107 100a 59a* 0.0004 100a 23b* 0.0001 108 100a 45a* 0.0001 100a 68a* 0.0025 109 100a 0b* 0.0001 96ab 0b* 0.0001 Different letters indicate significant differences (P < 0.05) between doses (TSB control, 105, 106, 107, 108, or 109 CFU/mL) within each column, and asterisks and P values indicate significant differences between treatment rows (without or with Trichodina sp. infection) within each isolate grouping.