February 15-18, 2009 Washington State Convention Center Seattle ...

GROTH PERFORMANCE AND RESISTANCE TO Strptococcus iniae OF NILE TILAPIA
Oreochromis niloticus FED VARIOUS DIETARY LEVELS OF THIAMIN
Chhorn Lim * , Mediha Yildirim-Aksoy and Phillip Klesius
Aquatic Animal Health Research Laboratory
USDA-ARS, MSA
Auburn, AL USA
Chhorn.lim@ars.usda.gov
Thiamin or vitamin B 1 functions in all cells as the coenzyme thiamin pyrophosphate that involves in the oxidative decarboxylation
of α-keto acids and the transketolase reactions in the pentose phosphate pathway. Thiamin has been demonstrated to be
essential in diets of fish, and quantitative requirements have been determined for several fish species including rainbow trout,
Pacific salmon, common carp, channel catfish, turbot, yellowtail and tilapia. Results of the few studies with homeotherms on
the effect of thiamin on immune function and disease resistance are contradictory. However, to our knowledge, no studies have
been conducted on the effect of dietary levels of thiamin on disease resistance in fish. Therefore, this study was conducted
to evaluate the effect of dietary levels of thiamine on growth performance, immune response and resistance of Nile tilapia
(Oreochromis niloticus) to Streptococcus iniae challenge.
An 8-week feeding study was conducted in flow-through 57-L aquaria with juvenile Nile tilapia (3.6 ± 0.2 g) stocked at a rate
of 35 fish/aquarium. Casein (vitamin-free)-gelatin based diets supplemented with 0, 2, 4, 8, 16 and 32 mg thiamin/kg were each
fed to fish in four replicate aquaria twice daily to apparent satiation. All fish in each aquarium were counted and weighed at 4
week intervals. At the end of 4, 6 and 8 weeks, 2, 2 and 3 fish/aquarium, respectively, were sampled and bled for determination
of serum pyruvate and lactate. At the end of week 8, another 3 and 4 fish/aquarium were bled for hematological and serum
immunological assays, respectively. Eighteen fish/aquarium (17 only for fish fed the diet without supplemental thiamin) were
intraperitoneally injected (IP) challenged with 100 µL of 1 x 10 4 CFU/mL of S. iniae and mortality was recorded daily for
14 days. At the end of the challenge period, four surviving fish/aquarium were bled for measurement of serum agglutinating
antibody titers against S. iniae.
Results showed that Nile tilapia fed the thiamin-unsupplemented diet had significantly (P < 0.05) reduced weight gain, feed
intake, feed efficiency and survival relative to fish in other treatments. These parameters did not differ among fish fed diets
supplemented with 2 mg thiamin/kg or more. Body protein did not differ among treatments, but lower body lipid and higher
moisture and ash were obtained in fish fed the diet without thiamin supplementation. Fish fed this diet also had significantly
lower hematocrit than those fed thiamin supplemented diets, but other hematological variables were not influenced by dietary
levels of thiamin. Serum pyruvate at weeks 4, 6 and 8 significantly increased in fish fed the thiamin-unsupplemented diet but
did not differ for fish fed other diets. Serum lactate, however, was not affected by dietary levels of thiamin. Serum protein, total
immunoglobulin, lysozyme and alternative complement activity, and post-challenge antibody titer were not affected by dietary
treatments. Cumulative mortality 14 days post-challenge was significantly higher in fish fed the thiamin-unsupplemented diet
but did not differ among fish in other treatments.
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