Aquaculture refers to the farming of aquatic organisms, including finfish, crustaceans, mollusks, plants, and algae for human use. It has been practiced by cultures around the globe for millennia. However, as global fish stocks decline, and the negative consequences of land-based animal agriculture become increasingly obvious, aquaculture has been touted as a sustainable solution to meet the dietary needs of a growing global population. Its proponents argue that the “blue economy” will revolutionize the global food system. Indeed, the farming of aquatic animals is the fastest-growing sector in agriculture in the United States and worldwide, with global production of aquatic species tripling over the past two decades. Amid such rapid growth, the significant animal welfare and environmental ramifications of an increasingly industrialized aquaculture sector have largely been ignored.
Aquaculture in the United States and globally
According to the most recent US Department of Agriculture census, the most farmed fish by weight are, in descending order, catfish, trout, and tilapia. Other commonly produced species in the United States are bass, carp, flounder, perch, red drum, sturgeon, and Atlantic and Pacific salmon (the census does not report weight for salmonid species, however). The states producing the most fish by value are Mississippi, Alabama, Texas, Idaho, and California. Asia is the largest producer and consumer of farmed aquatic species globally. China—considered the birthplace of fish farming—is particularly noteworthy in the diversity of production methods and species it farms.
The Food and Agriculture Organization of the United Nations (FAO) reported as of 2020 that farmed finfish totaled 57.5 million tons—49.1 million from inland aquaculture and the remaining 8.3 million from marine aquaculture and on-shore coastal aquaculture. The number of individual fish this represents is unknown, but a recent study concluded that between 78 and 171 billion farmed fish were killed in 2019. The majority of these (70–72%) have no protection under national animal welfare laws, and less than 1% have fish-specific legal protection at slaughter.
Fish Sentience
The scientific consensus surrounding the sentience of fish has evolved significantly in recent decades, with the best available evidence showing that fish are considerably more cognitively and emotionally complex than previously thought. Fish have specialized nerve endings called nociceptors that respond to harmful stimuli, indicating that they can perceive and respond to pain. Studies have demonstrated behaviors that show pain avoidance, such as reduced feeding, altered swimming patterns, and avoidance of painful stimuli.
While a fish’s brain is structurally different from a mammal’s in many ways, fish have analogous structures responsible for higher cognitive functions such as spatial learning, memory, decision-making, and emotional processing. Observations of fish behavior reveal that they can experience fear, stress, and even pleasure. They display complex social behaviors and form social bonds. Studies have revealed complex cognitive abilities in various fish species, including long-term memory, learning, and problem-solving. For example, fish in the wrasse family use anvil shaped rocks to crack open bivalves; other fish can learn to navigate mazes and recognize individuals.
The World Organization for Animal Health has established welfare codes for farmed fish in recognition of their sentience and the attendant risk of compromised welfare inherent in most modern animal farming operations. Yet, this recognition of sentience has not necessarily translated into consideration for fish on an individual level. In fact, the statistics of fish production have always been and continue to be reported in tons, rather than individuals, as farmed land animals are. Farmed fish have no legal protection under state or federal law in the United States.
Octopus farming is another significant animal welfare concern in aquaculture. Decapod crustaceans (lobsters, shrimp) are discussed below.
Welfare Implications of Fish Farming
Both raising conditions and methods of slaughter raise serious issues regarding the welfare of farmed aquatic species.
Water Quality
Unsurprisingly, water quality has a significant effect on morbidity, mortality, and welfare of fish. Health and welfare are compromised if their aquatic environment lacks an adequate amount of dissolved oxygen (allowing fish to breathe), contains excess ammonia from waste buildup, or is too acidic or too alkaline. Ideal water quality parameters vary between species.
Stocking Density
As with farmed terrestrial species, the amount of space available to each animal (stocking density) impacts welfare. High stocking densities have been shown to cause water quality deterioration, higher rates of injuries, increased inter-fish aggression, changes in behavior (e.g., reduced feed intake), and greater vulnerability to disease and parasites. In farmed salmon, for example, one of the largest welfare challenges is the control of sea lice, which proliferate in crowded net pens and feed on the fish’s living skin.
Stunning and Slaughter
Suffering and pain can be most acute at slaughter and during associated handling and transport. To ensure the least amount of suffering at slaughter, a stunning method that renders the animal immediately and painlessly unconscious (not merely immobilized) should be used before the killing cut.
Frequently employed methods of slaughtering fish, however, include conscious decapitation, evisceration or exsanguination by gill cutting; live chilling in ice slurry (leading to a slow death either by hypothermia or asphyxiation), immersion in water containing high concentrations of dissolved gas (CO2, N2, or CO), or asphyxiation via removal from water. None of the methods result in the animal being rapidly rendered insensible before death.
Although appropriate stunning methods vary between species, more well-studied methods include percussive (via a blow to the head if properly performed) and electrical stunning before cutting or decapitation. Percussive stunning, however, is subject to greater human error and can often fail. Thus, the preferred humane method is electricity, as it is more reliable and, if the voltage is high enough, can serve as the method of slaughter as well. The vast majority of fish are not stunned before slaughter, and while research has been undertaken for the development of humane slaughter methods for salmonids and trout, there is a gap in such research regarding humane slaughter of other aquatic species.
Environmental Enrichment
The most overlooked aspect of welfare in aquaculture is environmental enrichment—providing animals with sensory and motor stimulation to enhance their well-being, which also affects productivity. Enrichment allows animals to engage in biologically driven behaviors and promotes psychological wellness through physical exercise and cognitive stimulation and challenges. Enrichment can be divided into these general categories:
- Social – Allowing interactions with others of their species or with other species in a manner appropriate for the species and life stage. This could require the inclusion of material or structures for shelter/hiding and/or adequate space for schooling.
- Physical – Providing an environment that mimics the natural habitat in its complexity—for example, through shelter, plants, and substrate for nesting or burrowing.
- Sensory – Providing various visual, auditory, olfactory, and taste stimuli.
- Occupational – Providing mental and physical stimulation via the opportunity to confront challenges or puzzles, anticipate routine events, and control or manipulate their environment.
- Dietary – Providing variety in food type or delivery method.
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