Diminishing Species Life on Earth is largely possible thanks to the oceans. They produce most of the world’s oxygen, for example, and they remove carbon dioxide from the atmosphere. However, we are making life increasingly difficult for aquatic animals. Marine species populations are half of what they were in 1970, largely due to overfishing, pollution, and global warming , while freshwater species populations have declined an average of 83%!  Freshwater fishes have had the highest extinction rate worldwide among vertebrates, during the 20th century. 
Fishing Fishing is the cause of much of the harm. In addition to being horrifically cruel, fishing is recklessly indiscriminate. Along with the trillions of intended victims, estimates indicate that up to 40% of the global catch is non-targeted animals who are discarded overboard, many dead or dying.  Shrimp trawling is especially notorious for it. Trawling is a common fishing method whereby huge, heavy nets are dragged across the ocean floor, catching whoever is there and destroying fragile habitat.
Fish Farming Fish farming is viewed as a solution to diminishing wild fish populations but it is actually a huge part of the problem. Much of the global catch is used as feed for farmed fishes and shrimps (and chickens and pigs). Farmed fishes are kept in crowded pens and are often heavily infested with sea lice. The parasites can be transmitted to wild fishes, along with diseases. The farms pollute surrounding waters with feces, decomposing feed, antibiotics, and other harmful chemicals. Fishes who escape farms can outcompete wild fishes for food and other resources, and if they interbreed with them they may weaken their genetics. 
Pollution Other pollution includes nutrient runoff, largely in the form of manure generated by animal agriculture and used as fertilizer. Plastic pollution is another major problem, much of it consisting of abandoned or lost fishing gear. Plastic breaks down to microplastics, which aquatic animals often mistake for food or breathe in through their gills. These may become incorporated in their tissues and be ingested by predators, including humans.
“Trillions of pieces of plastic are choking the very lifeblood of our earth, and every marine animal, from the smallest plankton to the largest mammals, is being affected.” – BBC, October 1, 2018 
Global Warming, Acidification, & Deoxygenation Global warming is a grave problem, and recent research found local populations of marine animals are disappearing at double the rate of landbased species as a result of it.  Increasing carbon dioxide levels are increasing water acidification, interfering with skeletal and shell formation and coral reef creation. Warmer water also holds less oxygen, impairing the metabolism of fishes and other animals and reducing their ability to reproduce. “Oxygen levels in some tropical regions have dropped by a startling 40 percent in the last 50 years…with an average loss of 2 percent globally.” 
Noise pollution caused by sonic blasts from seismic surveys is another lethal assault to marine life, along with the hazards of ocean drilling and mining.
 Global Marine Populations Halved Since 1970, WWF Warns https://www.dw.com/cda/en/global-marine-populations-halved-since-1970-wwf-warns/a-18716798
 Living Planet Index http://livingplanetindex.org/projects?main_page_project=LivingPlanetReport&home_fla g=1
 Living Planet Report 2018: Aiming Higher https://wwf.panda.org/knowledge_hub/all_publications/living_planet_report_2018/
 Wasted Catch: Unsolved Problems in US Fisheries http://oceana.org/sites/default/files/reports/Bycatch_Report_FINAL.pdf
 Hatchery Fish are Less Successful at Reproducing in the Wild https://www.hakaimagazine.com/news/hatchery-fish-are-less-successful-at-reproducingin-the-wild
 Drowning In Plastic https://bbc.in/2IaJ7OF
 Global Warming is Hitting Ocean Species Hardest, Including Fish Relied On for Food https://insideclimatenews.org/news/24042019/climate-change-fish-local-extinctionmarine-species-hit-harder-land-animals-study-nature
 The Ocean is Running Out of Breath, Scientists Warn https://www.scientificamerican.com/article/the-ocean-is-running-out-of-breath-scientistswarn/
Fish Feel is the first organization devoted exclusively to promoting the recognition of fish as sentient beings deserving of respect and protection.