Abstract
In the coming decades, and despite advances in the selection of resistant strains and the production of triploid organisms, the temperature could seriously affect salmonid aquaculture. Lower environmental tolerance has been hinted at for triploids, but the physiological mechanisms leading to such differences, and whether they are translated to the individual level, are poorly understood. This study aimed to evaluate the effects of seasonal variations on the humoral and immune status in the blood (peripheral blood leukocytes) and plasma (antiprotease, lysozyme and peroxidase activities), the oxidative stress (catalase, glutathione-S-transferase, total glutathione and lipid peroxidation) balance in the liver, and the energy budget (sugars, lipids, proteins and energy production) in the liver and muscle of diploid and triploid Oncorhynchus mykiss. Leukocytes’ numbers changed with the water temperature and differed between fish ploidies. Peroxidase activity was increased in the summer, but lysozyme and antiprotease activities were increased in the winter. Concomitantly, antioxidant defenses were significantly altered seasonally, increasing oxidative damage at higher temperatures. Moreover, warmer waters induced a reduction in the energy production measured in the liver. Differences in feed efficiency, which have been previously reported, were confirmed by the low lipid and protein contents of the muscle of the triploids. In sum, the inherent trade-offs to deal with the seasonal changes culminated in the higher growth observed for diploid fish.
Highlights
Aquaculture production continues to grow in order to satisfy the global human demand for food, since fish protein ensures an energy source of easy digestion and high quality
A decrease in the number of neutrophil cells was observed from late summer to autumn, when the water temperature diminished from 22.0 to 15.4 ◦C (Table 1)
Significant interactions between the temperature and the type of fish ploidy (p = 0.002) lead to the triploid fish showing a significant increase in lymphocytes concomitant with a decrease of thrombocytes in the winter (6.6 ◦C) when compared with their diploid counterparts (Table 1)
Summary
Aquaculture production continues to grow in order to satisfy the global human demand for food, since fish protein ensures an energy source of easy digestion and high quality. Oncorhynchus mykiss production accounted for ~814,000 tonnes, corresponding to USD 3409 million in 2016 [2]. O. mykiss triploid fish started to be created in the middle of the 1980s, by thermal or pressure shocks applied to eggs shortly after fertilisation [5]. Their lower growth and survival in warmer waters were quickly noted [6]. Induced triploidy usually leads to a sterile fish, which is an advantage in aquaculture, since sterility ensures somatic growth and flesh quality, instead of the undesirable effects of energy allocation for sexual maturation, and prevents the establishment of escapees outside their native range [7,12]. Attaining a better understanding of the fish’s immune system and physiology is of utmost importance for adequate welfare and health management in sustainable aquaculture [14,15]
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