Growing lactobacilli in fish with varying diet.

I'm still focusing in on a specific research question, however, I have come up with a general idea. I'll be using at least two fish (probably goldfish) in the same tank. I'll either use some sort of dividing structure to keep them separated but keep the environments basically the same (water flow between). I won't have to do this if I can obtain fish which are uniquely identifiable; we'll see. I'll have two food sources, both of which will be inoculated with lactobacilli (need to choose species - there's quite a few). One food source will be mixed/enriched with a nutrient like fructooligosaccharide. Basically something that should encourage lactobacilli growth. One fish will get the food with the nutrient/bacteria and the other will get food with no nutrient and the same amount of bacteria.

Why would anyone do this? Just like as in the human gut, fish have a wide variety of bacteria. Some are beneficial, some not. The idea is to encourage dominance of beneficial bacteria in the fish so that when consumed by humans, the risk of food-borne illness is reduced. There's still going to be bacteria on the outside of the fish, but I believe (have to research more) the gut bacteria in the fish pose a larger problem. I'll be testing to see whether the nutrient enriched food yields more growth.

I inoculated a TSA plate with store bought yogurt containing probiotics and after two days this grew:

 I didn't see any other colonies other than this one. Gram Positive, catalase-negative rods. No glucose fermentation or motility results yet. But, most likely Lactobacillus casei.

On related note, supposedly goldfish aren't picky eaters. I might see if they will eat Labneh. I do, and I seem to stay healthy!