Hello, I am Dr. B, a licensed veterinarian and I would like to help you with your very interesting question.
Now the viability of feeding a non-traditional foodstuff (like cat food) is a bit questionable here. As I am sure you can appreciate, there has been no studies or research looking into the success of this type of diet on this species of fish (or any fish as far as I am aware) nor economical viability of doing so.
One of the first issues that comes to the forefront when considering this situation is that this is likely to be a food source who's cost would outstrip the value of the fish and profitability of resulting carcass. Therefore, if this were to be an economical venture, then it is quite likely that it would not be a profit making one.
If they are to be 'pets' or a hobby, then profit may not be a concern. In that case, we can focus on the nutrition practicalities of this diet for them. Tilapia are omnivorous fish, therefore this non-traditional diet could be a consideration here.
Now not all dietary components have been studied in these fish. For example, the level of carbohydrates required for their diet is not known. But as omnivores, they could likely tolerate the moderate levels of carbohydrates found in cat food. As well, taurine (an amino acid in all cat diets) supplementation has not been studies in these fish, since they do not require a dietary source due to making their own. So, we'd be unable to appreciate the effects of supplementing a non-essential amino acid may be. Though in regards XXXXX XXXXX required amino acids, most cat food diets will provide a degree of these (though how much will depend on the individual diet's make-up).
Turning to protein levels, one of the key elements of diets, this is a fish that does require different levels of protein at different life stages. That means that you will need to have established diets with appropriate levels of protein for each life stage that you are rearing. Therefore, if you were raising them from fry, they'd need ~45% (30-56%) protein, where juveniles require ~35% (30-40%) and adults require around 30% protein. So this could mean having to use multiple diets throughout the life of a fish.
That all said, I do have to point out one wee complication that you may experience with this particular species of fish. Where many of the aquaculture species require special requirements to reproduce, the tilapia is quite a prolific fish that do not require such special conditions. To the extent that in intensively reared farms, they have to either pre-sex the fish (to make sure the sexes are not mixed) or sterilize them with UV light to avoid being overrun with fish (partly because they want a uniform product but also because its not practical to try to feed multiple diets to a mixed population). So, while they do have the mixed blessing of being tolerant of high stocking density, do be warned that you could end up with more fish then you started unless these fish were UV sterilized already (which may be an issue if you are looking to do this for profit or have limited space).
Finally, I want to provide some further reading for you on Tilapia nutrition to aid you in deciding the best approach to feeding these fish with the resources you have access to:
South Dakota University's Tilapia:Environmental Biology and nutritional requirements (LINK)
University of Arizona's Introduction to Tilapia Nutrition (LINK)
Food & Agriculture Association of the UN's Tilapia Nutrition Article (LINK)
El Sayed's paper on -- PROTEIN NUTRITION OF FARMED TILAPIA: SEARCHING FOR UNCONVENTIONAL SOURCES (LINK)
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
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