Before you try your hand at speargun fishing it is important to understand the law. Some states like Hawaii, prohibit the use of most types of spearguns. However Hawaii does allow for one type of speargun to be used. That device is called an Hawaiian Sling and it operates much like a bow and arrow does on land. The device resembles a slingshot more than a speargun and its use is allowed because the energy of the device is stored in rubber tubing as opposed to a wooden or fiberglass shaft. Other states like Florida limit the use of certain types of spearguns. In Florida the use of powerheads or bangsticks, which are firearms adapted for underwater firing is strictly prohibited.
Most states allow for spear fishing but restrict the types of fish that can be caught to non game fish. Some examples of non-game fish are bluegill, buffalo, carp, drum, gar, green sunfish, and suckers. These fish are also referred to as coarse fish. For example, a state with fairly run of the mill rules on this is the state of Iowa. Iowa allows speargun fishing of all year round in large streams and non-flowing waters like lakes and ponds There is some controversy surround using these for catfish. Using spears to fish catfish is prohibited in some states but is allowable in others. Sport fish like bass, walleye and pike are generally considered to be off limits to speargun fishing in most states.
States also regulate the number of points or barbs that can be used on a single spear. Most states have adopted a three point and two barb rule, and for this reason most spears used for fishing resemble a small trident. While speargun fishing is generally acceptable in most areas, it's a good idea to check with your local DNR to find laws specific to your area before you go out and start fishing.