Another myth: You can't overfeed fish because of their instinct to survive.
And let's add to this the twin myth: that it is good for fish to be kept on permanent starvation levels because that is how they live in the while. No, it isn't: in the wild, food supplies fluctuate. If they stay permanently lower than a population needs, that population will stabilise itself, by fish ceasing to breed, and by fish dying off, and sometimes by fish growth being stunted. Which is not what the aquarist had in mind.
There's the third myth that its beneficial to starve your fish every now and then- this is only true for some fish species/types, like some predatory or large fish out there, but for small fish like guppys and platys its really not that great for them as they only have short little stomaches/guts and quickly go hungry. In the wild they are used to a small but relitavely constant supply of food, so small regular meals are best for them- many people think its only beneficial to give fry small regular meals, but for small adult fish out there in general its also beneficial for them to get small regular meals.
I find that small regular meals are more ideal for small fish, while relatively large not so regular meals are beneficial for larger fish who have long guts that can easily handle not going with food for a day or two(many large fish have simply evolved to be large so they can have long guts just for this situation). But you still have to take the fish's natural habitat into consideration as this does not always hold true.
Many large plecs out there live in hot climates in the wild, where throughout a part of the year their lake/river dries up and the plec has to dig itself a hole in a mud bank to hide in it while the lake/river dries up (sort of like a lung fish survival stategy), so it can wait out the lack of water and food in a wet or semi-floaded mud hole in a bank out of the glaring heat and killer sun.
This can last for months in some countries. I remember seeing all this on a wildlife documentory series called 'Survival"(looked quite old, maybe 80's or 70's or even earlier judging from the film quality and things), they also showed kribs in the same climate. Kribs live in a similar climate to the large plecs and catfish on this particular documentory, although the adult kribs do not have any survival stategy like the catfish- they breed/spawn just before the lake/river dries up and lay their eggs in the lake/river bed.
The kribs always die during the dry season as their lakes and rivers dry up but their eggs make it through surviving in damp areas of the river/lake bed- when the waters and rains return, the rivers and lakes are full of dried dead adult kribs and other fish that didn't make it through the dry season, causing an algae bloom when the waters return- this makes ideal food though for the newly hatched krib fry as they feast on their dead parents and algae, and also for other fish returning hungry to the lakes and rivers
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But is starvation always good for these types of catfish/plecs? No, because plecs like common and sailfin plecs grow a considerable amount in their first year (an 1inch+ a month usually), they do this because in the wild they would need to grow an aweful lot before the droubt/dry season sets in so they can be big enough to cope with the dry season- too small and they don't have the size or physical energy to make it through. But this is ok because during the wet season there is usually plenty of food to do this.
So starving young/growing plecs or ones under a year old is not a good idea because this is ideally not somthing that is supposed to happen, and in general young plecs that don't get a good diet or enough food in aquariums can fall short of their ideal max size, and would naturally not survive in the wild if this happened.
So with plecs its important to give them a varied good regular supply of food when they are young and growing, but to give starving/fasting day once a week or so and increase the protein in their diets if they are omnivorous (which most plecs and catfish are) after they have attained their max size and are designed/evolved to live with this way of life/diet- this is not a vital or particually important part of keeping some of teh larger catfish species out there, but many have evoled to live this way so it may be beneficial for them.
"Sigh"...theres so much to fish diet
! I don't think you can put any straightforward rules with fish and feeding, as there is so much to take into consideration
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