Experimental Streptococcus iniae infection of hybrid striped bass (Morone chrysops X Morone saxatilus) and tilapia (Oreochromis niloticus) by nares inoculation
Jj. Evans et al., Experimental Streptococcus iniae infection of hybrid striped bass (Morone chrysops X Morone saxatilus) and tilapia (Oreochromis niloticus) by nares inoculation, AQUACULTURE, 189(3-4), 2000, pp. 197-210
Streptococcus iniae infection was evaluated in hybrid striped bass and tila
pia following experimental, bilateral inoculation of a virulent isolate of
S. iniae onto their eyes or into their nares. Inoculation of eyes did not r
esult in mortality or disease signs in either species. In contrast, mortali
ty and disease signs were observed in both species following nares inoculat
ion Hybrid striped bass were susceptible to 4.8 x 10(3) S. iniae colony for
ming units (CEU), an inoculum 100 times lower than that affecting tilapia.
We observed decreased mortality of hybrid striped bass administrated 4.8 x
10(5) CFU dose of S. iniae. Following S. iniae infection, the disease signs
observed in hybrid striped bass and tilapia were erratic, serpentine, risi
ng and falling, and head-up swimming, slow acceptance or refusal of food, l
ethargy and darkened skin. We did not observe exophthalmia, eye opacity or
body curvature. We were able to recover S. iniae from either nares, eyes, b
rains, or head kidney of 87.5% and 66.7% of the morbid hybrid striped bass
and tilapia, respectively. Both hybrid striped bass and tilapia produced si
gnificant anti-streptococcal titers 14 days post nares inoculation with 4.8
x 10(3) CFU of S. iniae. Successful experimental S. inaie infection of fis
h following nares inoculation suggest that nares may be a potential route o
f S. iniae infection in cultured fish species. This route of experimental i
nfection for S. iniae has not been previously described in fish. (C) 2000 E
lsevier Science B.V. All rights reserved.