Aquaculture is one of the fastest-growing food production sectors globally and provides about half of the global fish supply meeting the needs for high-quality protein and essential nutrients. However, challenges such as changing climate, disease emergence and poor water quality affect health, growth and welfare. These challenges can be exacerbated by multiple stressors affecting the organisms’ physiological and behavioural responses and their interactions with the environment. But how can we ensure that aquaculture is sustainable in facing many challenges? How can we cope with the multiple stressors that threaten the health and productivity of aquatic farmed species? Minimizing stress and optimizing stress resilience would be the best option to ensure aquaculture sustainability and profitability in the face of multiple stressors.
Stress: a constant challenge
Aquatic farmed species (fish and shrimp) inhabit a pathogen-rich environment they must navigate daily. As a result, they are exposed to a wide range of pathogenic organisms, including bacteria, viruses, protozoa, etc., which induce stress. Besides, other factors alter the self-regulating process by which biological systems tend to maintain stability while adjusting to conditions optimal for survival in aquaculture species. Fighting against stress is a continuous challenge for aquaculture species causing an imbalance in the intestinal ecosystem, a risk factor for pathogen infections (Fig 1). Climatic factors also aggravate the impact of stressors depending on the production system’s type, location and intensity. Stressors in aquaculture can emanate from aquaculture practices and environmental conditions. Environmental stressors are either abiotic (salinity, rising temperature, oxygen depletion) or biotic (predators, pathogens, invasive species), whereas common aquaculture practices that induce stress include handling, transport, crowding and sorting.
Fig 1. Stressors and the impact on aquaculture
Mechanism of stress response
Stress elicits behavioural and physiological responses, one of the primary and essential mechanisms organisms require to maintain homeostasis. However, pushing stress response mechanisms too far can harm fish and shrimp’s health or be maladaptive, culminating in pathological conditions development. Many factors modulate stress response, such as the stressor’s type, magnitude and frequency. The individual characteristics of the organism, such as age, sex, size, genetic background and previous experience, also modulate stress response. From recognising a threat to homeostasis to the stress response and the consequences of stress, each category is initiated by the central nervous system. The current model of integrated stress response in all animals comprises adaptation and a fight-or-flight response to stress. While the adaptive response emphasizes the non-specific nature of the many reactive processes evoked by stressors, the fight-or-flight response involves activating the neuroendocrine system. Either way, plasma glucose is increased, representing an energetic cost in the case of farmed fish. A further extension of stress response elevates circulating cortisol, inhibiting growth and increased disease susceptibility by suppressing immune function. In most cases, a combination of stressors has additive, more than additive and antagonistic effects. For instance, high temperatures may increase the toxicity of ammonia or lower the resistance to pathogens which inhibit fish growth. At the same time, fluctuations in temperature and salinity have an antagonistic effect on shrimp growth, and their optimal combination depends on their interaction. Depending on the stressor’s type, intensity, duration, and frequency, aquaculture organisms may exhibit different responses: reduced feed intake and growth, changes in blood chemistry and hormone levels, behavioural changes and reduced social interaction. The optimal response for fish and shrimps depends on their species-specific characteristics and environmental conditions. The immune system of fish and shrimps must be able to react to a wide range of pathogens and function under a broad spectrum of environmental conditions.
Optimizing stress resilience
Nutrition plays a vital role in modulating the stress response and enhancing the stress resistance of aquaculture species. Therefore, the role of feed additives in achieving this cannot be overemphasized. Anta®Ox Aqua is a phytogenic feed additive that protects aquaculture species against stress and inflammation. Plant flavonoids in the diet can help fish cells to adapt to stress, by reducing inflammatory reactions. In accordance with this, the flavonoid-rich feed additive Anta®Ox Aqua enhances anti-oxidative capacity by reducing inflammation in farm animals and helps to mitigate the effects of inevitable stress in intensive aquaculture production. Besides, due to its antimicrobial properties, Anta®Ox Aqua has a far-reaching effect on a wide range of pathogens and function under a broad spectrum of environmental conditions. Numerous trials have shown how Anta®Ox Aqua positively influences aquaculture species’ stress resilience by having a beneficial effect on their immune and metabolic systems.
One indicator of stress is, for instance, an organism’s immune reaction to pathogens. The better the defence system functions, the greater the resistance to potential infections and pathogen-related stress. In an experiment with shrimp challenged with Vibrio parahaemolyticus for 30 days, the shrimps in the group receiving Anta®Ox Aqua showed a more marked response to the challenge than the control group. The higher the dosage of Anta®Ox Aqua, the more pronounced the immune response to Vibrio-induced stress (Fig 2). The robust immune response from the higher dosage of Anta®Ox Aqua enhanced survival rate and final live weight (Fig 3). Altogether, robust immune response and enhanced shrimp performance translate to higher profitable and sustainable production.
Fig 2. Anta®Ox Aqua reduces stress under a Vibrio-challenge condition as indicated by the immune response of shrimp (SOD; superoxide dismutase, THC; total haemocyte)
Fig 3. Anta®Ox Aqua improves the survival rate and performance of shrimp under a Vibrio-challenge condition
Choose the natural way
Stress is inevitable in aquaculture, whether it’s in a pond, tank, cage or other husbandry system. However, with proper planning and intervention, it can be effectively managed. Along with other management measures, feeding should always be a tool in the aquaculturist’s toolbox for stress management. Strengthening the stress resistance of the animals in a natural way, such as with Anta®Ox Aqua, is a helpful measure on the way to a more sustainable and profitable aquaculture production. Contact us for more information.