The Use of Dietary Additives in Fish Stress Mitigation: Comparative Endocrine and Physiological Responses

Abstract

In the last years, studies on stress attenuation in fish have progressively grown. This is mainly due to the interest of institutions, producers, aquarists and consumers in improving the welfare of farmed fish. In addition to the development of new technologies to improve environmental conditions of cultured fish, the inclusion of beneficial additives in the daily meal in order to mitigate the stress response to typical stressors (netting, overcrowding, handling, etc.) has been an important research topic. Fish are a highly diverse paraphyletic group (over 27,000 species) though teleost infraclass include around 96% of fish species. Since those species are distributed world-wide, a high number of different habitats and vital requirements exist, including a wide range of environmental conditions determining specifically the stress response. Although the generalized endocrine response to stress (based on the release of catecholamines and corticosteroids) is detectable and therefore provides essential information, a high diversity of physiological effects have been described depending on species. Moreover, recent omics techniques have provided a powerful tool for detecting specific differences regarding the stress response. For instance, for transcriptomic approaches, the gene expression of neuropeptides and other proteins acting as hormonal precursors during stress has been assessed in some fish species. The use of different additives in fish diets to mitigate stress responses has been deeply studied. Besides the species factor, the additive type also plays a pivotal role in the differentiation of the stress response. In the literature, several types of feed supplements in different species have been assayed, deriving in a series of physiological responses which have not focused exclusively on the stress system. Immunological, nutritional and metabolic changes have been reported in these experiments, always associated to endocrine processes. The biochemical nature and physiological functionality of those feed additives strongly affect the stress response and, in fact, these can act as neurotransmitters or hormone precursors, energy substrates, cofactors and other essential elements, implying multi-systematic and multi-organic responses. In this review, the different physiological responses among fish species fed stress-attenuating diets based on biomolecules and minerals have been assessed, focusing on the endocrine regulation and its physiological effects.

Dietary Oxidative Distress: A Review of Nutritional Challenges as Models for Poultry, Swine and Fish

“…Numerous dietary interventions based on optimal supplementation of antioxidative vitamins (E, A, C and B 2 ), micronutrients (Se, Cu and Zn) and feed additives are available to mitigate oxidative distress in poultry, swine [ 50 ] and fish [ 51 , 52 ]. However, due to the multiple factors that cause oxidative distress in farm animals, such as infectious diseases, management stressors (temperature, density, or transport) and dietary manipulations, it is difficult to show a consistent dietary antioxidant intervention response.…”

Physiology: An Important Tool to Assess the Welfare of Aquatic Animals

“…In the case of fisheries and aquaculture, consumers are demanding more (environmentally) sustainable and fair-trade products, which also includes animal care. There are interesting alternatives to improve/mitigate physiological stress responses in aquaculture, such as the use of natural antioxidants [ 142 ], and other dietary additives [ 117 , 143 ]. Similarly, the use of essential oils from plants with sedative properties seems to attenuate the physiological responses inherent to fish handling and cultivation [ 144 ].…”

Stocking Density Induced Stress on Plasma Cortisol and Whole Blood Glucose Concentration in Nile Tilapia Fish (Oreochromis niloticus) of Lake Victoria, Kenya

“…Elevated plasma cortisol, therefore, indicates that chronic stress occurred in HSD-reared O. niloticus [16,26]. Plasma cortisol is actually a good acute stress marker [41], with adrenaline considered as the stress hormone and cortisol, the adaptive hormone [42]. Figure 2 clearly demonstrates variation in the trend of the cortisol concentrations with subsequent HSD samples against lower but increasing cortisol concentrations in subsequent LSD samples.…”