The subtleties of the loricariidae diet is not an easy concept to grasp—in the wild, multiple species can live in the same vicinity which would all be described by the casual aquarist as “suckermouthed”, yet each, even those of the same genus, are completely enclosed within their own niche, with a feeding regime all to their own. This, of course, must be the case, lest their only be one species of pleco per river. A well outlined piece of literature documenting this delicate balance (and, I might add, an interesting read for any catfish enthusiast), is Mary E. Power’s work on algae grazing catfish of Panama. Here, she talks about Panama’s Rio Frijoles, which houses four species of loricariidae-Chaetostoma fischeri, Hypostomus plecostomus, Ancistrus spinosus, and Rineloricaria uracantha. Very minor intricacies in feeding habits, such as the inclusion of insect larvae in the diets of one species, and night time versus daytime foraging allows for a hefty population of each without sacrificing resource consumption. Alas, I digress.
Fortunately, in the home aquarium, many species can be appropriately acclimated to human offered fare without much hassle, and most will even share the same foods (though this is to be taken in to consideration when dealing with animals of vastly different feeding types). As a general rule, therefore, most loricariids can be dealt with on a genus by genus basis when considering diet regimens, thus, without further ado;
Ancistrus group/chaetostoma group/pseudancistrus group and derivatives (hopliancistrus, dekeyseria, lixothus) -periphytonic grazers inhabiting consistently shallower waters, where the natural awfuchs makeup is represented largely by algal growth and decaying vegetation. Thus, a diet rich in fiber and other vegetable products is preferred, although, as with other grazers, microrganisms are consumed in the process of grazing, and so, protein may be offered, though with some care. An old fry feeding trick that may be an interesting way of stimulating natural foraging behavior is to paint egg whites mixed with vegetable flake onto aquarium safe tiles, let them dry, and place them in the tank. This makes a great substitute for biofilm.
Leporacanthicus group (megalancistrus, pseudacanthicus, acanthicus, and arguably spectracanthicus)-these closely related genera are almost exclusively invertebrate-feeders, specializing in feeding on snails, small to medium sized crustaceans such as river prawns, predatory insect larvae, worms, etc, and sponges. In accordance, these fish prefer high protein, low fat fare; mollusks and crustacea commonly available in the fish markets are fine, though I personally prefer farmed white fish (freshwater). Many genera in this group, as previously stated, feed heavily off of freshwater porifera, and in the process, shave off a fair amount of wood, also found in gut analysis. This may explain why some of these animals seem to be more prone to intestinal blockages than other carnivorous species. To remedy this, vegetables should be provided either fresh or prepared alongside other staple foods.
Hypostomus/pterygoplichthys/psuedorinelepis/peckoltia -nondescript feeders inthe home aquariua that will take anything and everything. With unspecialized villiform teeth, these fish are suited to rasp, sift, and even, at times, gouge. From the sand sifting aphanotolurus and squalliforma, to the wood-grazing hypostomus cochliodon, all of these fish, regardless of habitat, are dietary generalists in the home aquaria and feed on both vegetation and protein. Both should be fed heartily to ensure that specimens grow while staying bloat-free.
Scobinancistrus/hypancistrus/oligancistrus/psuedacanthicus-these are the generalized carnivores, so to speak. Some are adept scavengers, others, skilled predators (large scobinancistrus, for example, have been referenced to have plucked small, free swimming fishes from the water column above them), and all can tolerate relatively high levels of fat and crude protein. However, in optimal conditions, they should still be fed relatively high quality, lean foods, akin to the dietary recommendations given to the aforementioned leporacanthicus. Similarly, fiber should still be provided, as their natural diet still allows for more fibrous victuals, including beans, seeds, and nuts, which are commonly consumed by all three.
Panaque/lasiancistrus/certain hypostomini and pterygoplichthyini-wood. Softer hardwoods such as many of the Malaysian bogwood imports, as well as common softwoods such as birch (sap free, of course), are preferred by these fish. Needless to say, other foodstuffs should be offered as well, perhaps even mixed in with said wood in a creative fashion. I have heard of individuals making their own pelleted foods by binding shaved wood and dried foods with gelatin to good success.
various peckoltia/baryancistrus/parancistrus-these limnivores feed on organic material deposited onto various aquatic surfaces by decaying vegetation and animal matter, along with the an assortment of macro and microorganisms found alongside this debris. These animals seem to have developed a meatier diet. Henceforth, high-protein foods should be fed at least once a day, in addition to a heavy feeding of vegetable matter, corresponding with the dietary mixture found in the awfuchs consume by these fish. Like their shallower water, more herbivorously inclined relatives, they should be fed frequently, corresponding with their grazing lifestyle.
In addition, keep in mind that many loricariids are highly secretive fishes that require a certain secure sensibility before willing to venture out and search for food--even if this means starving to death before an appropriate dining environment comes their way. Thus, newly acclimated fish need to be fed at night, or, at the very least far away from the prying eyes of the concerned (and rightfully so), but oftentimes meddling aquarist. Toss the food in and just walk away. This is best done in a hospital quarantine type environment that allows one to monitor the presence of food after a suitable amount of time, and to reduce tankmate competition until the fish is suitably adjusted. Needless to say, specimens should only be purchased that are in the prime of health, with full bellies and skittish behavior.
This is a more or less comprehensive list to the dietary needs of subfamily hypostominae, disregarding the rarer fish (cordylancistrus, neblinichthys, etc.) or the veritable scientific trash heaps (ancisti, hemiancistrus, etc.). Hypoptopominae and loricariine require more specialized care than what this article can possibly offer, so someone will probably have to write such an article another time. Enjoy.