VOICE OF PROFESSIONALS

HEALTH AND WELFARE IN AQUACULTURE

Aquaculture production is in a process of expansion as demand increases globally. Nevertheless, the intensive production of fish requires carefully monitored and controlled environments that, if not adhered to, may lead to stressed animals, compromising their health and survival. Animal health and welfare is a vital component of aquaculture, and is greatly impacted by environmental conditions and the basics of aquaculture.

Throughout history, producers have learned about animal husbandry through direct observation, as with cows and poultry, etc. However, as aquatic animals live underwater, direct observation has not been possible until recently. New technology has allowed producers to get a better look into their animals’ well being, and in turn, take better care of them. Improving the welfare of farmed fish (e.g., by reducing stress) can result in enhanced productivity. Therefore, applying correct management protocols is important for the economic success of this industry.

Intensive production may involve decreased environmental quality, including increased fish density and the appearance of production-related diseases, which are challenges faced by aquaculture. Domestication could lead to lower stress levels of the fish population for certain aquaculture environment. However, domestication may impair stress coping when fish experience a change in that environment. Therefore, the effects of multiple concurrent stressors, the process of domestication and the mechanisms associated with stress responsiveness are aspects that still need to be investigated in cultured fish. This article aimed at expanding general knowledge on the physiological responses of cultured aquatic animals to current practices and showcase latest technologies to improve conditions, fish health and welfare.

Fish health is strongly influenced by water quality, quality and amount of feed provided, husbandry and management practices. Disease outbreaks occurs as a result when fish experiences more than on stressors like reduced DO levels, poor water quality  and suboptimal densities, creating an imbalance between host, pathogen and environment. Cortisol is believed to be the main hormone mediating the physiological stress response in vertebrates. Sustained swimming activity at optimal speeds is associated with improved growth and lower secreted cortisol levels in various fish species.

Water quality

In addition to swimming, other factors impact fish homeostasis and may act as stressors. Among them water dissolved oxygen levels, temperature and stocking density are relevant factors under intensive aquaculture production. Water quality is considered to be one of the most important factors contributing to fish health. Fish have an intimate relationship with their environment. They are in close contact with their surroundings, making them sensitive to pollution and poor water quality.

Stocking density

Fish naturally exist and flourish within schools, they are different from terrestrial animals. They gravitate toward living in conditions in close quarters. However, with that being said, every system has a carrying capacity and should not be overstocked. Overly dense areas of production can have a negative impact on the farmed animal’s health and welfare. Every species is different in this respect, no one density ratio works for all. Hernández-Perez et al. showed that high stocking density in rainbow trout alters liver metabolism, a response also modulated by circadian rhythms. This study confirmed that high stocking density induces a stress response that is finely, differently and time-dependently regulated by glucocorticoid pathways. The circadian oscillator located in the liver was affected by the stressor, modulating the energy partitioning. Likewise, Martos-Sitcha, Simó-Mirabet et al. demonstrated by using metabolic and transcriptomic approaches that moderate hypoxia in gilthead seabream (Sparus aurata) produces a hypometabolic state with a negative impact on feed intake and growth rate, effects that were intensified with high stocking density.

Skin, gills and gut – A health indicator

The fish skin is a multifunctional organ with highly relevant physiological roles. Skin, gills and gut  have different structure and functions, they exhibit defense mechanism appropriate to the challenge posed by the environment so that animal  maintain an optimal health status. Kulczykowska summarizes the current knowledge of the skin function as a cutaneous stress response system, where cortisol, melatonin, and derived peptides act together to protect the organism against unfavorable conditions. The study of the various skin functions along with the impact of environmental and biotic factors is an exciting research area rapidly expanding due to its relevance in cultured fish. Sanahuja et al. investigated the response of the skin mucus proteome in the gilthead seabream exposed to changes in water temperature. Authors found that proteins associated with a stress response were up-regulated in fish exposed to low temperatures. However, proteins related to metabolic activity were down-regulated in response to cold, evidencing depressed skin metabolism. Results show a partial loss of mucus functionality under chronic cold exposure, which may affect fish welfare under farming conditions. Interestingly, parameters measured in the skin mucus can be used in a non-invasive approach to assess fish welfare.

Disease control

Unfortunately, when any type of animal is surrounded by other animals, disease outbreaks can occasionally happen. One of the main issues consumers hear about farmed fish is that they contain antibiotics, and therefore are unhealthy for humans to eat. Naturally, if their animals contact diseases, producers want to mitigate it as efficiently as possible. In some cases, the most humane way to do so is with antibiotics. The judicious usage of antibiotics is the best route for certain cases. It can be what is best for the animal and will help them recover. Judicious use of antibiotics, best management practices, and regulations include a withdrawal period  in which the fish cannot be harvested while medicine is still in their system.  Withdrawal periods are set by governing agencies such as the US Food and Drug Administration (FDA).

Functional Nutrition

Fish under stress releases cortisol that induces cascade of biochemical events to protect animal and draws tissue reserves of minerals and vitamins. The depleted trace mineral and vitamin reserves hampers the enzyme function during stress. Applying targeted nutrition is often used to provide additional defense strategy to limit and prevent particular disease. It can also be effective in limiting the negative secondary impact of disease without the need to resort to therapeutic interventions. These strategies are known as functional feeds. It strengthen and support natural immunological defenses of animal. As mentioned above it manages secondary effects and limits the impact of disease and reduce mortality. While it was not practical to treat whole population of anemic seabream affected by Microcotyle sp. in the Mediterranean with chemotherapeutic, the fish were when fed chelated iron diet which boost the hematocrit level sufficiently and enabled adequate respiration and restore blood oxygen levels, reducing mortality and achieving growth recovery.

Certification programs

The best avenue the aquaculture industry has come up with to monitor these variables is through certification programs. Certification programs like Best Aquaculture Practices (BAP) and Aquaculture Stewardship Council have created strict standards that producers must meet across the production cycle. The BAP certification program holds annual audits for facilities. Auditors hold the companies’ practices up against the standards on animal health and welfare, in addition to the other three pillars of sustainability. Companies do not receive their certification unless each of the standards are met. As mentioned previously, blanket sets of standards for all species will not produce meaningful results. This is why BAP has different standards for individual farmed species. Certification programs have become the policing system within the industry. Certifications allow consumers to feel confident in their seafood purchases.

Technology

As the industry continues to progress, new technologies continue to develop, making seafood farming more efficient and ensuring animals’ welfare along the production chain. Three primary types of technology have moved the industry along. Drones can be utilized for monitoring offshore fish farms or inspecting cages for damage. Sensors monitor underwater data such as water pH, salinity, oxygen levels, turbidity and pollutants (examples: Osmobot, eFishery, Sense-T, BiOceanOr). Finally, blockchain, which is a series of records of transactions across the supply chain, has enabled consumers to have access to transparency into where their seafood comes from. Technical solutions aiming to monitor fish welfare using less-invasive and non-lethal procedures by employing sentinel organisms are novel tools to be implemented in aquaculture. Martos-Sitcha, Sosa et al. described the design and validation of a reprogrammable and miniaturized device that can be attached to the operculum of gilthead seabream and European seabass (Dicentrarchus labrax). The authors reported how this device recorded and quantified the activity and respiratory frequency in fish kept in rearing tanks after its corresponding validation with swimming respirometry. Tagging the fish with this device was shown to have a minimal and transient impact, demonstrating that this miniaturized device could be a suitable tool when characterizing the physiological and behavioral responses of fish leading to improved performance and welfare in farmed species.

Conclusion

Successful fish farmers understand the signs of stress in their fish and work to understand and minimize them. Animals’ stress can lead to disease outbreaks and losses of animals, which not only financially hurts the producer, but it is also harmful to the animals. As these results are bad for the animal and producer, it is in the producer’s best interest to ensure that their animals are happy and healthy.

Animal health and welfare policies may seem overwhelming at first glance. There are so many species involved in the seafood industry that no one solution can help every single species. A positive development for finfish might end up harming shrimp. What’s best for one species is not necessarily best for all. For this reason, aquaculture includes a huge variety of species farmed in varying production systems (cages, ponds, RAS, etc.). Meaningful progress to improve animal health and welfare must come from a place of extreme understanding of the species at hand. Moreover, identifying and taking steps to mitigate the risk factor of an individual site play a vital role in the success of the operation.