There is a wealth of gear and techniques, both ancient and modern, for collecting freshwater fishes. Methods commonly used by ichthyologists to collect specimens for study are:

1. Straight seines

The net is often 5-15 feet long (but sometimes much longer), 5-6 feet deep, with a 1/16 to 1/8 mesh size. Heavy lead weights along the bottom (lead line) keep the net close to the substrate and bouyant floats along the top (float line) help keep the net extended. The straight seine may be stretched between two poles (brailles) or simply maneuvered by two people whereby each person loops the end of the lead line around his/her foot and holding the float line up with one hand. Seining typically involves one or two people setting the net downstream of a particular habitat (e.g., rocky riffle, submerged snag of woody debris). One or more people then violently disturb the habitat to scare the fishes into the net which is then lifted out of the water to catch the fish. Alternatively, two people may pull the next through the water (either with or perpendicular to the current) towards shore to trap fish in the water column. Seining is an incredibly enjoyable way to catch fish.

2. Bag seines

The bag seine is longer than the straight seine (typically 30-35 feet) and has a large bag (typically 6 x 6 x 6 feet) sewn into the center. Bag seines are most effective for pulling over large sandy beaches, particularly at night in the tropics. They also may be used to sample large shallow slackwater habitats with relatively smooth bottoms. The fishes get trapped in the bag as the net is pulled onto shore. Alternatively, a bag seine (or long straight seine) may be stretched between two boats, dragged through the water and pursed to trap fishes living in the water column or disrupted from the substrate.

3. Gill/Trammel nets

Gill and trammel nets are long nets (>50 feet, usually much longer) made of multifilament (usually multiple strands of nylon filament twisted into a single strand) or monofilament (single clear strand similar to fishing line) and . The net has float (top) and lead (bottom) lines and the mesh may be of a single size (e.g., 1 inch square) or of different sizes (i.e., experimental gill net). A gill net is a single net and a trammel net consists of 2-3 layers of netting (e.g., slack small mesh inner netting between two layers of large mesh netting). The nets are usually set in deep slack water and remain stationary, allowing fishes become entangled in the mesh as they try to swim through.

4. Dip nets

Dip nets are often used to sample shallow waters with dense aquatic vegetation. The net is thrust into the vegetation to scare out hiding fishes into the net. Alternatively, dip nets are useful for collecting small fishes that hide or nest in or under rocks in shallow water. The net is simply placed downstream of the rock, the rock is lifted, and the fish usually scares downstream into the net. Or, if the fish is hiding in the rock, the rock may be lifted from the water which usually prompts the fish to exit into the net below. Dip nets also are used with backpack electroshockers - but, only ones with wooden handles (or else the user may be shocked).

5. Cast nets

Cast nets are an effective way to catch fast-swimming fishes that easily scare and are too swift for seining. The net is circular with a 3-12 foot diameter, small mesh (1/4-5/8 inch) and a series of lead weights around the perimeter. The center of the net is attached to a rope held by the thrower. When properly thrown the cast net opens up into a perfect circle before hitting the surface of the water, then quickly sinks to trap the fish beneath. As the net is pulled out of the water the fish get entangled in the mesh. There are many techniques for acheiving the "perfect circle" that require time and practice to master, especially for the larger cast nets.

6. Trawl nets

Trawling is the best method for catching fishes that live in the deep channels of large rivers. A small to large net is suspended between two trawl doors or "otter boards", each separately tied to a long tow rope. The top of the net is suspended by floats and along the bottom is a weighted footrope. The center of the net has a long funnel-shaped sock in which the fish become trapped. The sock, or cod-end, usually has a finer mesh size to retain the fish. The entire trawling rig is carefully thrown overboard and may be pulled by a large boat or a sturdy canoe with a good outboard motor. As the trawl is pulled in the water, the hydrodynamic otter boards act as wings to spread the net horizontally as the float line and footrope maintain the net's vertical spread. Trawling in large rivers, particularly those in South America, has resulted in the discovery of many new species of deepwater fishes.

7. Trot lines

A trot line is simply a long stretch of rope/cord onto which shorter lines with baited hooks are spaced. The trot line can be floating (leaving the hooks dangling in the water) or sinking (hooks sit on the bottom) and set in slack or running water. They are best left overnight to catch fishes that feed after sunset and in the early morning hours.

8. Traps

There is a wide variety of "fish traps" (hoop nets, wooden catfish traps, steel or collapsible minnow traps), some of which are examples of the earliest gear used to catch fishes. The premise is relatively constant and involves submerging a baited enclosure of wood, netting or wiry mesh that has one or two small funnel-like entrances (throats). Fishes swim into the enclosure, but usually cannot find their way out.

9. Electrofishing

Considered cheating by anglers, electrofishing is a particularly effective and efficient way to catch swift or large fishes that live in habitats difficult to sample with more "traditional" methods (e.g., large cataracts with strong currents and boulder-rubble substrates, or open waters with abundant submerged aquatic vegetation). Electrofishing involves passing electric (usually DC) current through the water to stun or draw fish to the surface where they can be netted (usually with a dipnet). A variety of gear may be used to generate the electricity including electric seines and dipnets, backpack electroshockers (battery and gas powered), larger boat-mounted electroshockers, and even old crank telephones.

10. Bow and spearfishing

Some fishes are best caught using traditional techniques commonly used by indigenous cultures (e.g., Native-Americans). Bow and spear fishing is often used to catch deep-bodied fish that move into shallow riffles to feed or large fishes that "sleep" in shallows near shore at night.

11. Dam and dewater/Fish poisons

This is probably the most labor intensive technique pioneered by early fishermen/women. It involves carefully selecting a braid or side channel of a larger river. A dam is built across the upstream end of the side channel to divert the water into the main channel and sometimes a net or trap is placed at the downstream end of the side channel. The water in the side channel quickly recedes because of the diversion and the remaining water is bailed out by hand. In cases, however, where the side channel is very large, the fishermen/women simply rely on the diversion to partially dewater the dammed channel. Once the dammed channel is dewatered, the fishes are easily grabbed either by hand or with dip nets. Sometimes indigenous cultures will introduce a natural poison (rotenone) to the water to "slow down" the trapped fishes. Rotenone is derived from several different tropical leguminous plants that are pulverized or "beaten" to release the poison into the water.

12. Hook and line

This is pretty much speaks for itself. In the hands of the skilled fisherman/woman, any pole, some line and a hook with the right bait, coupled with patience and luck, will yield fish (a reel is optional). For most ichthyologist anglers, size does not matter (but species does).

13. Handfishing or "Hogging"

This is probably the most enjoyable and challenging method for catching fish. Many fishes, particularly catfishes, hide in cavities in submerged rocks or hollow logs often during the day. The handfisherman/woman carefully prods such cavities with their hands to find the secretive fish and then slowly trys to "extract" the fish from its hiding place, sometimes by inserting a finger or hand into the fishes mouth. Sometimes you can simply lift the wood or rock out of the water onto the bank, then carefully inspect it for any residents. In a modified version of "hogging" one may use a snorkel and mask to view fishes underwater in swift currents and then try to pin resident fishes beneath rocks with one's hands.

14. Commerical/ornamental fishers
Local aquarist shops and fish markets

Wholesale fish markets and aquarist shops, the kinds found near rivers or ports that receive catches directly from the commercial/ornamental fishers, are great places to find interesting specimens particularly of large commercial species and rare aquarium species. Locals know best how to fish such species and the ichthyologist can benefit from their experience and work, usually at a nominal cost.