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Fishes are some the most interesting animals on the planet. They thoroughly dominate the diverse rivers, lakes and oceans that cover over 70% of the Earth’s surface. The term fishes is very generic- referring to five classes of animals who are more distantly related than they appear. All have mastered the skills of survival and evolved to a point of near perfection. In the process, fishes have morphed into a myriad of shapes, colors and patterns.
Anatomy and Physiology
Over 25,000 species of fish are alive today. They inhabit every aquatic environment on the planet-from the near freezing Polar Regions to sweltering hot springs; from shallow ponds to the mysterious pitch-black depths of the oceans. A life in water requires adaptations unlike any seen on land. Some of the most elementary adaptations are those associated with efficient movement through water. Most fish have a fundamentally streamlined body structure that is laterally compressed to reduce resistance. In addition, they have numerous mucous glands that secrete a slick film over their scales-acting to reduce friction and deter external parasites.
Watching fish swim can be mesmerizing. A wave of muscle contractions provides the thrust while a series of several fins enable them to maneuver through the water with extreme precision. By strategically displacing the surrounding water, the fins create a lift force that is equal to the fish’s overall mass.
Fishes senses are highly attuned to the physical properties of water. To successfully find prey and avoid predators, they must use all of their senses simultaneously. Their sense of smell is more accurately described as chemoreception-the ability to distinguish between a large variety of chemical compounds. This sense is integral to their survival as it aids in finding food, detecting predators and seeking mates.
Fishes have also been shown to have good memories, which can play a part in their survival as well. According to Kevin Warburton, a Charles Sturt University researcher in Australia, “Fish can remember prey types for months. They can learn to avoid predators after being attacked once and they retain this memory for several months. And carp that have been caught by fishers avoid hooks for at least a year…” 
One of the most unique traits that fishes possess is a sensitive lateral line system. A series of pores along the side of the body connect to canals that run through the bones of their skull. In the bones, an abundance of neurons process the faint vibrations of the surrounding water, and help them detect slight variations in pressure and depth. This system allows fish to swim in extremely large groups while appearing to move as a single mass.
The more ancient fishes are part of the class Condrichthyes. The skeletons of these fish are composed exclusively of cartilage-no bone. Included in this class are the sharks, skates and rays. Due to their dense tissues, buoyancy is a great challenge for these species. A large volume of liver oil, which is less dense than water, helps to compensate for their overall mass. These species also have a highly acute sense of electro-reception. Specialized nerve cells in the pores of the skin are able to detect weak electrical signals given off by other animals.
For a variety of reasons, Osteichthyes (bony fish) are considered more advanced than the cartilaginous fish. Their most notable advantage is the presence of a swim bladder. This air filled sac in their abdomen allows them to stay suspended in one place without using their fins. As they move vertically through the water, oxygen is added or removed to keep the body neutrally buoyant. This organ greatly reduces the fish’s energy requirements.
Stress, Pain and Fear Perception
In the scientific community, the question of whether fish are capable of experiencing stress, pain and fear is nearly undisputed. Over millions of years, fish have evolved complex adaptations for sensing and avoiding sources of adverse stimuli. The main scientific question has been whether fish experience any form of emotional state as a result of adverse stimuli. Increasingly, research is suggesting that emotional states may be more closely tied to primitive parts of the brain.
In an effort to further understand the animal welfare implications of modern fish farming, the European Union’s Food Safety Authority commissioned a review from the Animal Health and Welfare panel. The following paragraphs are a summary of their conclusions.
While stress is a normal part of life, animals must be able to sense the source and react accordingly in order to maintain homeostasis and survive. Fish have evolved many behavioral and physiological adaptations for coping with stress. Most of the adaptations are similar to those seen in other vertebrates, such as rapid and erratic movements, seeking shelter and chemical secretion.
Pain perception is a fundamental aspect of an individual’s short-term survival, as well as long-term survival of the species. Without the ability to perceive pain, an animal would have no interest in avoiding predation. In nature, fish exhibit a variety of defense and escape behaviors in their effort to avoid the source of pain. 
Fundamentally, fear is a cognitive process with many physiological consequences, such as increased heart rate and disruption of pain receptors. Like other animals, fish likely experience fear in anticipation of severe stress or pain.  While pain perception may be easy to recognize, fear of pain and the emotional states that result are far more complicated. Some animals, such as dogs, are rather overt in their emotional displays. However, most animals do not show their emotional state in ways that we can easily understand. Rather than assume that they are incapable of experiencing emotional states, many neurobiologists predict that their emotional states are simply more subtle.
Fish Transport and Slaughter
Currently, there are no state or federal laws to protect fish from chronic stress, pain and suffering during rearing, transport and slaughter. In 2004, the European Animal Health and Welfare panel reviewed and analyzed the most common methods of fish transport and slaughter. The following quotes were taken from the panel’s conclusions:
“Many existing commercial killing methods expose fish to substantial suffering over a prolonged period of time.”
“Many fish killing processes are designed for commercial efficiency rather than welfare priorities.”
“For many species, there is not a commercially acceptable method that can kill fish humanely.”
“Evidence indicates that electrical stunning systems do not induce a sufficiently long period of insensibility to ensure the fish dies before recovery of consciousness.”
“Shooting and electric harpoon for farmed tuna, hydraulic shock and hypoxic stunning have poor welfare implications.
The panel also noted that anesthetics are not allowed for any fish who may enter the food system.
As with other industrially farmed animals, fish that are hunted and raised for meat experience unnecessary pain, fear and suffering. Wild caught fish suffer slow, painful deaths after becoming entangled or impaled in netting and hooks. Commercial fishermen continue to hunt most species at a highly unsustainable rate; in some cases, compromising the future survival of the species. Fish raised in aquaculture are unable to swim in open waters and eat natural foods. The cramped conditions cause severe stress and weaken immune function.
While we may have very little in common with fish, the commonalities we do share are vital. Like us, fish have an interest in avoiding pain and are strongly motivated to find low stress environments. Both commercial fishing and Aquaculture are inherently stressful and unsustainable practices that cause unnecessary suffering.
Food Empowerment Project encourages everyone to appreciate the beauty and complexities of all fish as well as choose a diet free of animal products, which is one of the easiest ways to bring this suffering to an end.
 Retrieved 2/4/10 from http://economictimes.indiatimes.com/environment/wild-wacky/Fish-can-remember-things-for-months-Scientists-/articleshow/5453230.cms
 Scientific Opinion of the Panel on Animal Health and Welfare on a request from European Commission on General approach to fish welfare and to the concept of sentience in fish. The EFSA Journal (2009) 954, 1-26 Retrieved 1/2/2010 fromhttp://www.efsa.europa.eu/en/scdocs/doc/ahaw_op_ej954_generalfishwelfare_en.pdf
 The EFSA Journal (2004), 45, 1-29, Welfare aspects of the main systems of stunning and killing the main commercial species of animals. Retrieved 2/9/13 from http://www.efsa.europa.eu/de/scdocs/doc/45.pdf