Selection of lactic acid bacteria as candidate probiotics and in vivo test on Artemia nauplii

Lactic acid bacteria (LAB) were isolated from rotifer cultures in a marine hatchery to search for potential probiotics for marine animals. Fifteen strains were first selected among a total of 55, according to antibacterial activity against Vibrio sp. Among eight strains identified as Lactobacillus casei, four were highly adhesive, suggesting some ability for surface colonization. The other strains were identified as Lactobacillus plantarum, Lactobacillus dextrinicus, and Leuconostoc sp. To validate probiotic potential, Artemia were challenged against pathogenic Vibrio alginolyticus, with or without one of six selected LAB strains. The six strains protected Artemia against the pathogen, to some extent on condition that nutrient enrichment was provided. La. casei BR51 and X2 were preferred, as they were efficient even in the absence of nutrient supply. La. casei X2 was finally selected as candidate probiotic, due to the best growth performances of Artemia, with or without the pathogen.     

Commercial single-cell proteins either as sole food source or in formulated diets for intensive and continuous production of rotifers (Brachionus plicatilis)

Commercial Spirulina, Chlorella, and a methanol-grown yeast were tested as sole food source for the rotifer Brachionus plicatilis. Some good results were obtained, but only with medium salinity (18%) and none with seawater (35‰). In comparison with a constant supply of food, different adjustments of the food level to the population density were tested: a proportional and continuous or stepwise adjustment and a less proportional one. The less than proportional adjustment was found to be more advisable for a continuous culture with a daily renewal of a quarter of the volume. The three single-cell proteins appeared to be suitable with 35–55 rotifers produced per ml per day. However, the food conversion was poor: in the best cases 4.2 g of food were required per 10⁶ rotifers produced. In practice, two formulated diets were preferred for mass culture trials in 60-l tanks: the first (P 72) included 40% Spirulina, 40% yeast and different additives; the second was composed of 67% of diet P72 and 33% of the freeze-dried alga Platymonas suecica. The production was 44 and 35 rotifers, respectively per ml per day, with 3.6 and 2.9 g of food, respectively per 10⁶ rotifers,produced. Freeze-dried algae did not appear to be necesary for rotifer production, but the nutritional quality of such rotifers should be investigated.