Background: Binding of serum components by surface M-related proteins, encoded by the emm genes, in streptococci constitutes a major virulence factor in this important group of organisms. The present study demonstrates fibrinogen binding by S. iniae, a Lancefield non-typeable pathogen causing devastating fish losses in the aquaculture industry and an opportunistic pathogen of humans, and identifies the proteins involved and their encoding genes.

Ichthyophthiriasis is a common parasitic disease of freshwater food and ornamental fish. This study examined the ionic effects of an induced infection of ichthyophthiriasis in goldfish Carassius auratus. The whole‐animal net Na+ and Cl– fluxes were measured from 12 goldfish each day for 5 d. The numbers of branchial mucous and chloride cells were also determined histologically. Two days of postexposure to 200 theronts/mL resulted in significant net losses of Na+ and Cl–. Whole‐body ionic effluxes were then reduced over the subsequent duration of the experiment. There was a general increase in the numbers of branchial mucous cells as reinfection progressed. Branchial chloride cells were elevated in infected fish, indicating some degree of compensation in response to infection. This suggested that acute ionic disturbances occurred in the host fish as a consequence of different stages of the life cycle of the parasite; the host exhibited a suite of physiological and morphological changes to compensate for parasitic infection.

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This study aimed to evaluate the effect of probiotic on growth and survival of tilapia (Oreochromis niloticus) against Streptococcus agalactiae infection. The test materials used were commercial probiotic bacteria and Streptococcus agalactiae. The probiotic bacteria were administered by mixing into the feed with a dose of 0 mL (without probiotics), 10 mL / kg of feed, 15 mL / kg of feed and 20 mL / kg of feed.  Feed was given 3 times a day at 08.00, 12.00 and 16.00 for 21 days. After that, the challenge test was done with Streptococcus  agalactiae bacteria by cohabitation. Bacteria with a density of 107 cells / mL were mixed into the water and allowed for 2 hours. The result showed that B treatment (10 mL / kg of feed) gave the best result with 93,33 percent of  survival rate. Statistical analysis showed that the survival of fish in treatments B, C and D was significantly different from treatment A (P <0.1). However, there was no significant difference between treatments B, C, and D. It was also found that the addition of probiotic in feed did not affect the growth of Nile tilapia (Orechromis niloticus). Keywords : Probiotic bacteria,  nile tilapia,  Streptococcus  agalactiae, growth,  infection

The purpose of this study was to detect the presence of bacteria Aeromonas sp in tilapia (Oreochromis niloticus). Nine fish with an average body weight of 150-200 g were used in this study as samples. Sampling was conducted at three different locations which were representative of fish culture sites located on Lake Tondano. The number of sample gathered from each location was and 3 fish which were taken randomly. Fish samples were taken by using a scoop, then the samples were taken alive by placing in an oxygen-filled plastic separately and taken direcly to lab Fish Disease Control and Environmental Center, Tateli, Department of Marine and Fisheries of North Sulawesi province, for examination the presence of bacteria. Isolation of bacteria were conducted by taking samples from gill and kidney. This study was carried out from April - July 2013. Identification of the presence of bacteria was done through a series of observations of colony morphology and gram staining of bacteria, followed by a series of biochemical tests: oxidase test , catalase test , test TSIA , H2S production test , indole test , motility test , citrate test, and test O/F. It could be concluded that 22.22 % of farmed nile tilapia in Lake Tondano were infected with the Aeromonas sp with the following percentage from each site: Paleloan village 7.40% , 7.40% Toulimembet village, and 7.40% Eris village. Keywords: Aeromonas sp, isolation, nile tilapia, floating net cage, Lake Tondano