from glucose, fractose, salicin, sorbitol, xylose, trehalose, manitol or maltose. It did not hydrolysed starch or arginine. It grows on nutrient agar contained 0.0, 3, and 5% NaCl, and grow at 45ºC. It did not haemolyside blood. M. luteus was isolated from gonads of apparently healthy O. niloticus.
Psuedomonas sp was gram negative, bacilli, single, motile, oxidative, facultative anaerobe and oxidase-postive. It produced acid from glucose and did not produce acid from sucrose, salicin, arabinose, lactose, galactose, sorbitol, xylose or manitol. Arginine hydrolysis, ornithine and lycin decarboxylase were negative with it. It isolated from intestine of apparently healthy O. niloticus.
The in- vitro probiotic activity:
Two isolates, M. luteus and Psuedomonas sp were examined for a probiotic activity against the pathogenic A. hydrophila in vitro. It showed inhibitory effects against A. hydrophila. However, Psuedomonas sp gave larger inhibition zone (9 cm) than M. luteus (4 cm).
Safety of the isolated probiotics:
Two isolates of the probiotics were harmless to O. niloticus as no clinical signs or mortalities were noticed following challenge via I/P route. M. lutius and P. species were safe to fish in comparison to the control as show in table (1) which gives mortality rate 10%.
Results in Table (2) showed that the final weight, weight gain and specific growth rate of O. niloticus increased significantly when fed a diet containing M. luteus only (P<0.05., 10.16g/fish final weight, 7.773 g/fish weight gain and 1.61 %/day SGR). These values decreased significantly in the fish group which fed a diet containing Psuedomonas sp (8.02 g/fish final weight, 5.626 g/fish weight gain and 1.34 %/day SGR). The O. niloticus in the group which fed a diet containing mixed bacteria ( equal amounts of Psuedomonas sp and M. luteus) were slightly increased (8.976 g/fish final weight, 6.59 g/fish weight gain and 1.47 %/ day SGR) but less than control group (9.39 g/fish final weight, 6.99 g/fish weight gain and 1.536 %/day SGR).
Survival rate was decreased in O. niloticus fed with diet contained P. species (95%) then mixed diet (97.5%), while control group and fish fed with diet containing M. luteus were 100% (Table 2).
Feed intake was approximately similar and ranged from 11.14 to 11.68 g feed/fish except the fish group fed a diet containing M. luteus in which the feed intake was slightly increased (12.28 g feed/fish, Table 3). On the other hand, the least feed conversion ratio (FCR) was observed with fish group fed diet contained M. luteus (1.58), while the highest one was observed at control, the fish group that fed with Psuedomonas sp, and that fed mixed bacteria with insignificant difference (1.69, 1.74 and 1.98, respectively). Table (3) indicated that there was a significant increase in protein efficiency ratio (PER) with the diet containing M. luteus (2.156). Protein efficiency ratio with the diet containing Psuedomonas sp showed the least PER (1.72). The control and mixed groups had protein efficiency ratio of 2.026 and 1.96, respectively.
Concerning the proximate chemical analysis of whole fish body, table (4) showed that the moisture content was approximately similar (27.87-31.25%; P>0.05). Crude protein content in whole fish body was approximately similar (53.16-55.58%).