Live food for feeding aquarium fish.
Live foods are traditionally defined by aquarists as living organisms harvested in natural water bodies, quarries, ponds, temporary puddles, rivers, as well as in drainage ditches and settling tanks in filtration fields. These are mainly ciliates and oligochaetes, insect larvae, and mollusks, which feed on the organic matter of silt and decaying animal and plant remains—animal organisms dwelling at the bottom of water bodies, living in the upper layer of sediments and silt, known as zoobenthos.
Another group of animals serving as food for aquarium fish includes organisms that form part of zooplankton, inhabiting the water column. Due to their small size, they appear sluggish, as if hovering in the water. Zooplankton includes cladocerans and copepods, certain groups of worms and tunicates, and larvae of invertebrates, amphibians, and fish. Planktonic organisms either completely lack organs of locomotion (passively floating) or have weak locomotion organs that cannot withstand water currents.
Zooplankton and benthos are the main invertebrate communities that ensure the normal functioning of aquatic ecosystems, their self-purification, and serve as a food base for many fish species. Zooplankton usually consists of three systematic invertebrate groups: rotifers (Rotatoria), cladocerans (Cladocera), and copepods (Copepoda). Plankton (from Greek planktos – wandering) is the aggregate of organisms inhabiting the water column of continental and marine water bodies, incapable of resisting current transport. Plankton includes both plants—phytoplankton (including bacterioplankton)—and animals—zooplankton. Plankton is contrasted with bottom-dwelling organisms—benthos—and actively swimming animals—nekton. Unlike the latter, plankton organisms are incapable of independent movement or their mobility is limited. In freshwaters, a distinction is made between lake plankton—limnoplankton—and river plankton—potamoplankton. Nauplius (from Greek nauplios – an animal with a shell) is the planktonic larva of many crustaceans.
Planktonic organisms are generally small in size and have a large specific surface area. In addition, special adaptations help them hover in the water: the presence of various bristles, spines, and outgrowths that slow down sinking and increase the specific surface area; a reduction in heavy substances in skeletal structures and shells; the presence of gas inclusions (blue-green algae, larvae of certain mosquitoes, etc.); an abundance of water (some rotifers). Freshwater plankton consists mainly of protozoa, rotifers, cladocerans, and copepods, etc. Zooplankton possesses high nutritional qualities.
Live foods have many advantages. For the most part, they have a high nutritional value, and the essential vitamins and other nutrients they contain remain intact and are not destroyed during processing, unlike what happens during the preparation of some dry foods. They are rich in beneficial fibers and nutrients necessary for breeding fish. Live foods such as bloodworms, tubifex, phantom midge larvae (coretra), daphnia, and Artemia nauplii are extremely favored by fish.
Representatives of the crustacean class make excellent food. Usually, species from two orders are fed: Cladocera and Copepoda. Cladocerans are more commonly called daphnia. Their size is often less than a millimeter, making them indispensable for feeding fry. For instance, dry matter of daphnia (Cladocera) contains 58% fat, while cyclops (Copepoda) contain 66.8% protein and 19.8% fat. Furthermore, live foods are rich in vitamins, allowing fish fed on them to grow rapidly and develop vibrant coloration. Fish possess natural feeding instincts. Therefore, they generally react more lively to moving prey than to stationary food.
The main negative aspect of feeding fish with live foods is the risk of introducing diseases and parasites. Pathogenic microorganisms (bacteria, viruses) and parasites may be present in the internal organs or body tissues of organisms used as live food. Additionally, the natural water in which such live foods are harvested can itself become a source of diseases or parasites.
Along with live food, fish disease pathogens will inevitably enter the aquarium. After all, these foods are harvested from natural water bodies, most of which have their own fish populations, and in nature, rare fish are free of parasites. In aquarium conditions, fish usually fall ill very severely and, as a rule, die without qualified treatment. Therefore, unless you are an expert in treating fish ailments, refrain from using live foods. It is relatively safe to feed fish only with Artemia nauplii (young, newly hatched brine shrimp). However, they are very small and suitable only for fry and small fish, and creating conditions at home to hatch crustaceans from eggs is a troublesome task.
Special water treatment or cleansing of live foods can rid them of certain parasites and pathogens, but these procedures cannot be entirely relied upon, as they cannot eliminate all potential disease agents found in feeds. Freshwater crustaceans such as cyclops (Cyclops) may harbor parasitic worm larvae (helminths), and tubifex worms (Tubifex) are known to carry pathogenic viruses, bacteria, and even some protozoan parasites. Thus, the risk of introducing diseases into the aquarium along with live food is quite significant, and aquarists must always keep this in mind.
Aquarists should pay special attention to observing fish during the spring and summer periods when disease pathogens reproduce most intensively in natural water bodies where live food is harvested, thereby increasing the likelihood of introducing them into aquariums. Perform mandatory sorting of live food to remove ichthyophagous predators: leeches, dragonfly larvae, water beetles, bugs, mollusks, and other animals. When feeding fish with live hydrobionts, avoid introducing the water containing the live food into the aquarium. Feed the fish using tweezers (tubifex, bloodworms, etc.) and separate nets, without submerging them into the aquarium water. Daphnia, bloodworms, and tubifex are frequently available for sale; tubifex is best purchased frozen or freeze-dried, as live tubifex can spread fish diseases.
The risk of infection will be greatly reduced if the acquired live food is immediately frozen. Freezing for a few days will kill most fish ectoparasites. However, you are not insured against bacterial infections. Quick-frozen bloodworms, if stored at -12°C or lower, retain their color, shape, and—judging by the enthusiasm with which fish eat them—palatability.
You can catch invertebrates with a fine-mesh net, but be careful not to introduce predators like dragonfly larvae into the aquarium, which could eat your fish. To increase shelf life, any live foods should be stored in the refrigerator, on a balcony, or in a dark, cool place. Admittedly, storage time can thus be extended only slightly, up to 7–10 days. For long-term storage (up to 1 year) of bloodworms, deep freezing is applied.
Artemia. Branchiopod crustaceans (Artemia salina). Decapsulation of Artemia cysts.
Main types of food for aquarium fish. 
