Numerous trials were conducted with microorganisms known as probiotics to improve culturability of food species and to improve human health and welfare. Appropriate probiotic applications were shown to improve intestinal microbial balance, thus leading to improve food absorption (Parker, 1974; Fuller, 1989), and reduced pathgogenic problems in the gastrointestinal tract (Lloyd et al., 1977; Goren et al., 1984).
The final weight, weight gain, specific growth rate, survival rate feed intake and protein efficiency ratio were increased among O. niloticus fed a diet containing M. luteus, so it may be considered as a growth promoter in fish aquaculture. These results agree with Rengpipat et al. (1998) and Prabhu et al. (1999) were reported that the probiotic treated group enhancing growth rate of shrimps and maintaining water quality parameters. Survival of shrimps was significantly greater in treated group compared with the control group. Lactic acid bacteria had an effect as growth promotor on the growth rate in juvenile carp but not in sea bass (Noh et al., 1994). Also, Emterococcus. faecium had also been used to improve growth when fed to sheat fish, Silurtes glanis L (Bogut et al., 2000).
Probiotics may stimulate appetite and improve nutrition by the production of vitamins, detoxification of compounds in the diet, and by the breakdown of indigestible components(Irianto and Austin, 2002a). Streptococcus faecium improved the growth and feed efficiency of Israeli carp (Noh et al., 1994 and Bogut et al., 1998). A several probiotic species were used including Lactobacillus sp. (Jonsoon, 1986) and mixes cultures (Lessard and Brisson 1987).
The use of probiotics can improve the nutrition level of aquacultural animals and improve immunity of cultured animals to pathogenic microorganisms. In addition, the use of antibiotics can be reduced and frequent outbreaks of diseases can be prevented. Riquelme et al. (1997) studied the naturally occurring bacteria which are able to promote the growth and survival of Argopecten purpuratus larvae by inhibiting the activity of other bacteria that flourish in hatchery cultures.
Tovar-Ramírez et al. (2004) notced that the growth of larvae of sea bass fed 1.1% live yeast as a probiotic was increased than control group. Also, survival of larvae was significantly higher than the control. Kennedy et al. (1998) showed that the addition of a gram-positive probiotic bacterium increased survival, size uniformity, and growth rate of marine fish larvae (snook, red drum, spotted seatrout and stripped mullet).
Much less work has been directed at the immunological enhancement of defence mechanisms of fish by probiotic bacteria or the protective mechanisms of probiotic bacteria in fish (Nikoskelainen et al., 2003). Also less work has been directed at the blood parameters.
Results of the present investigation showed that Psuedomonas sp in diet of O. niloticus caused a decrease of blood parameters (RBSC, HB and Hct). These results are in agreement with those of Palikova et al (2004) who observed pathmorphological findings (haemorrhages in the skin, eyes, hepatopancreas and in swim bladder) in the common carp after exposure to Cyanobacteria extract. Ishikawa (1998) showed that the spleen, liver and kidney of unhealthy fish held fairly severe infection , suggesting that haematopoiesis was also severely affected and this affected the peripheral blood by decreasing erythrocyte volume. Also Ranzani-Paiva et al (2004) showed that the decrease in erythrocytes count and haematocrit of Nile tilapia inoculated with Mycobacterium marinum may lead to a