That food, the Xtreme Aquatic Foods
Beef Heart Flakes, is 46% protein, if it's
Neon Tetras or Cardinals lets say for instance, you'll wind up with fat fishwith a diet like this as a staple food. neons or Cardinals will have a better conversion ratio, of of a 25-35% protein. something as high as 40% for conditioning to spawn.
The Xtreme Aquatic Foods Beef Heart Flakes, also has about 10% fat. it's not necessarily a bad thing, but again it's a weight gainer.
this kind of food would be more suited for like
Cichlids,
Barbs. wider bodied more robust fish. For tetras an example would be like exodons where they are all "go go go" and you dont' want them nipping on everyone else and each other all the time but do want them wide bodied and robust and never hungry.
A lot of the tetras are omnivores, or insectivores, kind of small or slender, not much girth to them. for most tetras, something with 25-35% protein, 5-10% fat, low to no carbohydrates (0-5%), for fillers, spinach,
spirulina, algae.
If it has insect proteins, or plant proteins in the composition it's so much better than fish proteins, or mammal proteins. nutrient composition, the
vitamins and minerals and fatty acids are important too, what you'd want to avoid is flours, and meals in the ingredients, this is all just fillers and low quality fish or shrimp scraps. Size of mouth can aid in figuring out what they would or wouldn't eat really, many tetras, it's small things. algae, daphina,
brine shrimp, scuds, copepods, the little guys that are eating algaes also, so it's sort of a "gut load" for the greens/plant matter.
BUT, there are reasons to feed the kind of food that's high in protein and fats. lets say you have a lot of neon tetras, a big school. Maybe not everyone gets to eat on every feeding, some are getting out competed at times, this higher protein and fat content tends to keep everyone heavier and more robust and when missing meals, they aren't dropping like flies. the "extra" that they carry in body mass supports their immune system, and gets them over "dry spells" of food where they could be out competed at times and declining in health from poor nutrition.
That food would also have it's uses for like conditioning females for spawning, where you'd want to get them plumped up for spawning.
It's not "Horrible", just if used regularly as a staple food, it's going to create fat fish especially out of the males.
And yes, the BSFL would be a good source of protein for all your fish, however I think you'd need to grind them up for the fish if they are
betta and tetras, maybe working it into a home made
fish food with a gel product. I mean, you can do crickets, grasshoppers, nightcrawlers, mayflies. there a whole bunch of insects you can buy or collect up and grind up and freeze in cubes (with tank water) or go the gel route. the limitation on the insects is size of them and the fishes mouths really, but you can do quite a lot with a food processor or blender to break whatever insects you have down into bite sized bits. Collecting insects has it's risk of contaminants like pollution or poisons,from the environment, so just use your discretion on that. if you have pest control outside, it's a no, if the area doesn't look healthy, it's a no. but there's a lot of free bugs out there for fish to eat was the point, and bugs are generally cheap feeders at the pet stores also.
I know lightning bugs are toxic to fish, not sure what else might be, but for sure they are a no-no, there's also some that just don't taste good also.
Some indoor bugs, people feed to fish or the fish just encounter them depending on how bad the problem is, I'd avoid the indoor bugs, unless you know you don't have poisons down and around, and haven't had any used int he nooks and crannies around the house in a really long time. otherwise yeah, fish eat bugs in the wild, bigger bugs get eaten by bigger fish, parts come off in that, that smaller fish can eat and they get the scraps from it foraging.. natural process.
Anyways, there's some info on here about feeding all kinds of things to fish, how to farm them also, how to make your own fish foods, plus the internet is full of information outside of this website. that food you got isn't a bad thing necessarily, I'm sure the store was thinking how hard it is to keep tetras alive in numbers, and how much to feed, and figured fat fish is better than starving fish.