Taking Care Of Shrimp Welfare In Aquaculture

Shrimp aquaculture occurs around the world, yet little is known about their suffering and behavior in a farming setting. This report aims to assess the most important factors related to shrimp well-being, focusing on whiteleg shrimps (Litopenaeus vannamei). It’s estimated between 171 to 405 billion whiteleg shrimps are farmed globally per year.

Farming Practices And Conditions

A common harmful practice in shrimp farming is eyestalk ablation. This practice involves crushing or cutting off at least one of the eyestalks in female shrimps to increase maturation and reproduction speed. Ablation may lead to physical trauma, stress, and weight loss, and it may also make offspring more vulnerable to diseases. Research has found that shrimps demonstrate wound-tending behavior such as rubbing the wounded area after being ablated.

According to the report, disease is another factor that strongly affects shrimps’ well-being. Common diseases include viral pathogens, such as white spot syndrome virus, yellow head virus, and infectious myonecrosis virus. Viral outbreaks can cause high mortality rates, with some farms reporting as many as 100% of their shrimps dying. Shrimps could also suffer from bacterial and fungal infections. To reduce disease outbreaks, the authors suggest giving shrimps probiotics and supplements to support their immune systems.

Stunning and slaughter practices are also a serious welfare concern. Shrimps are typically slaughtered through suffocation or chilling in water with ice. However, one study found that while chilling whiteleg shrimps reduced their heart rate, the stunning effect went away after returning them to warm water. It is also possible that ice-cold water paralyzes shrimps without producing an anesthesia effect. Tight packing and insufficient ice may lead to some shrimps dying of suffocation rather than being stunned by chilling. Lastly, chilling may cause pain due to a reduction in salt content as ice melts. While the evidence is limited, the authors argue that electrical stunning might cause less suffering. 

Lowering stocking density is another way to improve shrimp welfare. Providing too little space for shrimps to turn around or crawl impacts their natural behavior and induces stress. Lowering stocking density can also improve water quality, reduce disease, and decrease mortality. However, extremely low stocking density could also trigger dominance behavior and poor feeding responses. According to the authors, an optimal stocking density is 6 to 15 shrimps per square meter in a semi-intensive farm. 

To reduce shrimp suffering, environmental enrichments such as feeding methods that encourage natural behavior, hiding spots, and tanks with different shapes and colors should be considered. Substrates and sediments can also help enrich shrimps’ environment and improve survival rates. Sediments like sand combined with an artificial substrate can provide a burrow and serve as a source of nutrients. Tanks with a dark background and a round shape are recommended for whiteleg shrimps.

Improper transport and handling are likely to cause stress and injury, although data specific to shrimps is limited. Trawling shrimps can cause physical injury and packing them heavily for transport may lead to crushing and suffocation. The report argues that a maximum packing weight should be imposed to avoid injury.

Like other decapods, shrimps may be resilient when given insufficient amounts of food. However, when their nutritional needs aren’t met, shrimps may suffer from non-infectious diseases such as soft-shell syndrome and behavioral abnormalities such as aggression and cannibalism. In contrast, overfeeding can cause problems with water quality.

Water Quality

Another important concern in shrimp welfare is water quality. Factors affecting water quality include dissolved oxygen level, temperature, un-ionized ammonia level, pH (acidity), and salt concentration (salinity). The authors are highly confident that putting shrimps in water with low levels of dissolved oxygen is harmful and increases mortality. It is important to maintain dissolved oxygen levels between 5 and 8 mg/L to reduce susceptibility to disease and the build-up of toxic ammonia.

There is very strong evidence that a high un-ionized ammonia concentration is toxic for shrimps. It reduces their immunity, can damage their organs, and increases mortality. The recommended amount of un-ionized ammonia is below < 0.05 mg/L. Water acidity is another factor that should be considered. The pH level should be between 7.8 to 8.2. Higher pH levels could increase toxic ammonia. Sudden changes in pH levels can also be damaging.

Non-optimal water temperature, particularly high temperature, also negatively impacts shrimp health. High temperatures reduce the amount of dissolved oxygen and increase toxic ammonia, while very low temperatures or contact with icy water can be stressful and fatal. The report states that optimal water temperature should be between 28 to 30 degrees Celsius.

Furthermore, water salinity could impact shrimps’ health. However, experimental evidence regarding the effect of water salinity on shrimp welfare is inconsistent. Salinity can influence dissolved oxygen and toxic ammonia levels. Higher salinity seems to be better for shrimp survival but could also increase bacterial growth. Overall, a salinity range between 10% to 20% is recommended for whiteleg shrimps.

Shrimp Advocacy Takeaways

More research is required to better understand the effect of these farming practices and environmental factors on shrimps’ mental and physical health, as well as to come up with better measures of shrimps’ well-being. Because so little is known about shrimps and what can make their lives better in aquaculture, animal advocates can help by calling for more research. Meanwhile, for issues such as eyestalk ablation, disease, stunning, and slaughter where there’s evidence that existing practices are harmful, advocates can work with shrimp producers to adopt higher welfare standards.