There could be protozoan parasites involved here, like Spironucleus. Internal metazoan (worm) parasites come in two flavors: direct development and those that require additional hosts in order to complete their life cycle. The latter are rarely a long term issue with marine fish as the hosts aren't present for them to spread. The direct development parasites like nematodes can cause mortality over long terms. I recently saw some really nasty nematodes that migrated out of the fish's gut and entered the liver. Here is one issue though: if you are successful in killing off a large number of these worms, they can decompose and the fish dies of toxic shock.
I worry about just mixing general cure in food - you don't know the weight of the fish, nor the amount of medication being delivered, so the dose is therefore unknown I'm working on a medicated food paper for R2R, but it won't be ready in time for you to use it (sorry!). Here is what I have so far:
Medicated foods
Oral medications are an excellent way to target internal diseases of fishes. Marine fish absorb aquarium water, so in certain cases, they “drink” enough medication from the water to effect a cure. However, freshwater fish actively export water from their tissues and do not take in aquarium water, so injectable or oral medications are really the only delivery system that works for them.
Years ago, there were a variety of commercially available medicated flake and pellet foods. Currently, there seems to be only one product on the market, so aquarists are faced with either forgoing medicated foods, or making their own.
Presently, many aquarists try to soak their fish food in medication and then feed that to their fish. The trouble is that this can never really work. Oral fish medications are always dosed on an “as fed basis”, usually milligrams of medication per kilogram of fish biomass. In the case of soaking food in medication; the amount of medication per gram of food is unknown, as is the weight of the fish, and so is the amount of food being fed. With that many variables, a proper dose simply cannot be formulated.
Case history: (Just an example of the math involved)
An aquarium housing 13 rather small fish needed to be treated with oral antibiotics. The veterinary recommendation was to use erythromycin, dosed at 100 mg/kg fish body weight in the diet for 14-21 days.
The first step was to estimate the fish mass in the aquarium (in this case, but comparing to a known weight data set). 10 platies (about 5 g total) 1 goldfish at around 40 g, one or 2 danios at 2 g and one large tetra and 10 g, for a total mass of around 57 grams.
For the erythromycin dose, that works out to be 5.7 mg of erythromycin fed to the whole tank each day.
One usually assumes that the fish will eat around 3% of their body mass each day, so for this system, that works out to be 1.7 grams of food per day. Therefore, we need 5.7 mg in 1.7 grams of food, or 670 mg in 200 grams of medicated food.
Erythromycin is soluble in ethanol. Dissolving 670 mg of erythromycin in the smallest amount of ethanol possible and then spray it on to 200 grams of flake food and allow it to evaporate. The fish were then fed 1.7 grams of food daily (spread over three feedings).
Jay
