ISSUE FOCUS FEED & ADDITIVE MAGAZINE August 2025 31 es and the temperatures of the surrounding water. As a result, temperature increases will likely expose farmed fish, crustaceans and mollusks to chronic and acute thermal stress (Fernandes et al., 2023). Anthropogenic climate warming may interfere with critical biological and physiological processes, including metabolic rate, oxygen demand, oxygen solubility, thermal stress tolerance, immune response, reproduction, growth, nutrition and disease resistance (Mugwanya et al., 2022). The impacts are expected to be severe for farmed aquatic species with narrow thermal tolerance ranges, particularly those already living near their upper thermal tolerance limits, such as freshwater tropical species, which may be especially vulnerable to the ongoing challenges posed by climate change (Nati et al., 2021). Water temperatures exceeding the upper thermal tolerance limit of a species (Figure 1), particularly during heat waves, may surpass the critical threshold, ultimately leading to mortality (Cereja, 2020). Although there is no single mechanism explaining temperature-induced fish mortality, it may be caused by indirect effects (such as reductions in water oxygen levels or increased susceptibility to parasites and diseases) or at extreme temperatures by direct thermal effects on the fish’s physiology (Ern et al., 2020). For example, in midsummer, water temperatures in the southern Mediterranean (e.g., Turkey, Greece, Spain) can rise above 32°C, exceeding the upper tolerance limits of key farmed marine species in the region, such as European seabass and gilthead seabream, which grow optimally at temperatures around 25°C (Dülger et al., 2012). However, seabream appears to have a lower ability than seabass to acclimate and survive in the highly variable temperature conditions of the Mediterranean Sea (Kır, 2020). Studies on both species have shown antioxidant responses to thermal stress, but the specific antioxidant thresholds at which fish performance and fitness become compromised under climate change–induced temperature shifts remain unknown. Besides, models have shown that seabream would require more time to reach the minimum commercial size, where growth performance, harvest yield and return on investment may decline as climate change intensifies (Cubillo et al., 2021). Rising temperatures due to climate change, particularly in antibiotic resistance “hot spots” such as the Mediterranean Sea, may alter bacterial physiology, potentially leading to increased resistance to antibiotics (Pepi and Focardi, 2021). The harmful synergy between climate change and antimicrobial resistance can further drive the emergence, transmission and spread of infectious diseases, posing an increasing threat to human health (van Bavel et al., 2024). Mediterranean aquaculture is just one example to discuss the effects of climate change and heat stress on aquaculture. Concerns about the potential impact of climate change have also been raised in salmon farming regions such as North America, Chile, Norway and Tasmania (Calado et al., 2021). Meanwhile, low-latitude countries such as those in the Asia-Pacific region, which have limited adaptive capacity, are expected to be extremely vulnerable under future climate change scenarios (Troell et al., 2023). Turbot 23° Shrimp 32° Catfish 32° °C Seabream 30° 35 30 25 20 15 10 Seabass 30° Common Carp 21° Rainbow Trout 16° Salmon 16° Nile Tilapia 31° Figure 1. Maximum thermal tolerance limit for aquaculture species: Salmon and rainbow trout (16°C), common carp (21°C), turbot (23°C), seabass and seabream (30°C), Nile tilapia (31°C), catfish and shrimp (32°C) (Mugwanya et al., 2022; Kır, M., 2020)
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