Overfishing is catching too many fish at once, so the breeding population becomes too depleted to recover. Overfishing often goes hand in hand with wasteful types of commercial fishing that haul in massive amounts of unwanted fish or other animals, which are then discarded. Overfishing endangers ocean ecosystems. Secondly, unregulated fishing practices that result in grave harm include by-catch (as explained in the previous point) and Trawling. Trawling involves scraping along the bottom of the sea to gather fish. This practice is one of the major causes of destruction to marine habitats. Third, overfishing has led to a decrease in the population of productive fish, resulting in lesser stocking of the fish. Forth, bycatch leads to the capturing of marine animals that are not used or required. The animals may include protected or endangered species or species that are of little or no economic value. If caught, they are normally destroyed and discarded either in the water or ashore. Lastly, fish farming requires feed for reared fish. For example, you will need between four and eleven pounds of prey fish to raise just one pound of farmed salmon. With the rapid expansion of the aquaculture industry, prey fish population is reducing at alarming and untenable rates. According to some researchers, if this trend continues, fish farming will have outstripped the supply of fishmeal by 2020.