Fish is the main source of food in the open sea. There are some poisonous and dangerous ocean fish but, in general, fish are safe to eat when not feeding near reefs. Nearer the shore, especially around coral reefs, there are fish that are both dangerous and poisonous to eat.
Do not handle fishing line with bare hands and never wrap the line around your hands or tie it to a life raft. The salt that adheres to it can make it a sharp cutting edge that is dangerous to both the raft and your hands. Wear gloves, if you have any, or use a cloth to handle fish and to avoid injury from sharp fins and gill covers. Gut and bleed fish immediately after catching them in warm regions. Cut fish that you do not eat immediately into thin, narrow strips and hang them to dry. Dried fish stays edible for several days and often fish that does not taste very good when sampled just after the fish is killed may be more palatable after a couple of days drying. Fish not cleaned and dried may spoil in half a day. The organ meat (especially the liver) is most nutritious and easily digested so eat it at once. Fish with dark meat are very prone to decomposition. If you do not eat them all immediately, do not eat any of the leftovers. Use the leftovers for bait.
Never eat fish that have pale, shiny gills, sunken eyes, flabby skin and flesh or an unpleasant odour. Good fish show the opposite characteristics. Sea fish have a saltwater or clean “fishy” odour. Do not confuse eels with sea snakes that have an obviously scaly body and strongly compressed, paddle–shaped tail. Both eels and sea snakes are edible, but you must handle the latter with care because their venom is fatal. The heart, blood, intestinal wall and liver of most fish are edible. Also edible are the partly digested smaller fish that you may find in the stomachs of large fish, wash these first with seawater and then fresh water.
Fishing line. Use pieces of tarpaulin or canvas. Unravel the threads and tie them together in short lengths in groups of three or more threads. Shoelaces and parachute suspension line also work well.
Fish hooks. No survivor in a life raft should be without fishing equipment, but if you are, improvise hooks from any workable metal. It is even possible to make a fish hook out of the plastic casing from a ballpoint pen. Necessity being the mother of invention.
Fish lures. You can fashion lures by attaching a double hook to any shiny piece of metal.
Grappling hooks. Use grapples to hook seaweed. You may shake crabs, shrimp or small fish out of the seaweed. These you may eat or use for bait. You may eat seaweed itself but only when you have plenty of drinking water. Improvise grapples from wood. Use a heavy piece of wood as the main shaft and lash three smaller pieces to the shaft as grapples.
Bait. You can use small fish as bait for larger ones. Scoop the small fish up with a net. If you don’t have a net, make one from cloth of some type (like the arm from a shirt). Hold the net under the water and scoop upward. Use all the guts from birds and fish for bait. When using bait, try to keep it moving in the water to give it the appearance of being alive. Do not throw bait into the water if there are sharks around.
Fish at night using a light. The light attracts fish. Even the luminous glow of a wristwatch is effective but be wary of placing a hand into the water at night because of the risk of attack by sharks, moray eels, etc.
Daytime shade attracts some fish. You may find them under your raft because it becomes an island. As barnacles and weed grow on the base of the raft, it will become habitat for marine life. Fish like trigger fish and dorados will thump the bottom of the raft as they feed on barnacles and smaller fish. You have to learn to put up with this constant intrusion.
Improvise a spear by tying a knife to an oar blade. This spear can help you catch larger fish but you must get them into the raft quickly or they will slip off the blade. Also, lash the knife very securely to the shaft or you will lose it. Fish will be attracted to the raft and the best way of spearing them is to hang over the entrance to the raft and get them as they swim directly below you. Spearing directly down reduces the problems of refraction but you need to have great patience waiting for the shot and you need to move very fast to spear a fish. If you get a large fish, reach down, hold onto the handle of your knife and the fish then haul the fish aboard. The speared fish will fight and you have to develop a good technique to deal with it. Have some cloth ready to wrap it in and you need something hard to put beneath it. Stab into its spine to break it and hold onto the fish until you see its eyes glaze.
Always take care of your fishing equipment. Dry your fishing lines, clean and sharpen the hooks and do not allow the hooks to stick into the fishing lines. If you have made a spear, check the lashing every time you use it and after every catch.