Fishing methods will influence the quality and therefore usefulness of fish which is discarded. Gillnets, for instance which may be set at sun-down and lifted again at sun-up may have fish in them which has been dead for a number of hours. In tropical waters where sea temperatures can be in the mid 20s Celsius fish can be partially spoilt and may also be attacked by predatory species such as shark. This applies not only to any potential discards, of course, but also to target fish species. Indeed one of the reasons for discards at sea can be that target species are already spoilt before lifting the net.
The quality of trawled fish similarly will depend on time of soaking as well as such factors as the amount of fish in the cod end, the water temperature, the type of substrate etc. Kungsawan (1996) asserts that in Thailand, the quality of bycatch from otter trawl vessels catching shrimp as their main target is worse than that from pair trawlers or gill netters. This results in most otter trawl bycatch being used for fish meal, whereas bycatch from other shrimp fishing methods is more likely to be used for human foods.
The best quality fish at capture will be associated with fishing methods that remove fish from the water immediately they are caught and where fish are usually alive at this stage. These would include the various surrounding and lifting nets and some hook and line fisheries such as pole and line and hand lines. It is usually the case, for instance, that trawl caught fish will be less valuable than fish of the same species caught by hand line. Where fish are discarded from this type of fishery there is also a higher likelihood that they will be discarded alive, that is released, and that they may survive. The fact that they are released alive does not, of course mean that they will survive. Damage inflicted by the catching method may mean they will die later or fall victim to predators or disease because they are in a weakened state. The fact that that they may be released back into a different location and habitat may also mean that they have less chance of survival.
Fish caught and likely to be discarded are usually going to be treated badly so that their quality is not preserved. The possibility of using the fish for human consumption will normally only be possible if some sort of onboard preservation is used or the fish is unloaded onto carrier vessels, for instance, for swift movement to shore base facilities for preservation and processing.