Temperature effects on growth performance, feed utilization efficiency and nutrient retention of gilthead seabream Sparus aurata cultured under the Red Sea conditions
This study demonstrates that juvenile gilthead seabream cultured in Red Sea conditions exhibit optimal growth, feed efficiency, and nutrient retention at temperatures between 24°C and 28°C, while exposure to 32°C significantly impairs their biological performance, suggesting that aquaculture operations in the region should avoid southern, warmer areas.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the ocean as a giant, bustling kitchen where every fish is a chef trying to cook up its own growth. But there's a catch: the stove temperature changes. In the world of fish farming, scientists are constantly trying to find the "Goldilocks Zone" for water temperature—not too cold, not too hot, but just right. This sweet spot is crucial because water temperature acts like a thermostat for a fish's entire body. It controls how fast their heart beats, how much they want to eat, and how efficiently they turn their food into muscle. If the water is too chilly, the fish gets sluggish and stops eating. If it's too hot, the fish gets stressed, burns through its energy just trying to stay alive, and stops growing. This matters because millions of people rely on farmed fish for food, and as the planet warms, figuring out exactly how heat affects these animals is becoming a race against time to keep our dinner plates full.
Now, let's dive into a specific experiment where researchers played with the thermostat for a popular fish called the gilthead seabream, the kind often found on Mediterranean tables. They wanted to see what happens when you cook these fish in water that mimics the Red Sea, a place known for getting quite toasty. The team took juvenile seabreams, each weighing about 212 grams (roughly the size of a large smartphone), and split them into three different "hot tubs." One group swam in water at 24°C (a comfortable, mild day), another at 28°C (a warm summer afternoon), and the third in a sauna-like 32°C (a scorching heatwave). They fed them the same commercial diet and watched them for ten weeks to see who grew the most, who ate the best, and who turned their food into body mass most efficiently.
The results were a clear story of heat stress. The fish in the 24°C and 28°C tanks were the happy campers. They grew at almost the exact same speed, gaining about 198 grams each, and they looked healthy and plump. However, the fish in the 32°C tank were the ones having a bad day. They barely grew, adding only about 101 grams—roughly half the growth of their cooler-dwelling cousins. It's like trying to run a marathon while wearing a heavy winter coat; the fish at 32°C were burning so much energy just to deal with the heat that they had very little left over for growing.
The way these fish handled their food also changed with the heat. Interestingly, the fish at 28°C actually ate the most food, gobbling down about 4.1 grams per day. But despite eating the most, they didn't grow any faster than the fish at 24°C. This suggests that at 28°C, the fish were working harder just to stay alive, using up their extra snacks for maintenance rather than building new muscle. The fish at 32°C, on the other hand, lost their appetite, eating the least amount of food (3.3 grams per day). When the researchers calculated how well the fish turned food into weight (a number called the Feed Conversion Ratio, or FCR), the 24°C group was the most efficient, needing only 1.4 grams of food to gain a gram of weight. The 32°C group was the worst, needing a whopping 2.5 grams of food to gain that same gram. It's a waste of resources; the hot fish were eating more relative to their growth, or in the case of the 32°C group, eating less but still failing to grow.
The study also looked at what was happening inside the fish's bodies. As the water got hotter, the fish stored less fat and protein. The fish in the 24°C water had the highest body fat (16.0%) and protein (17.7%), while the 32°C group had the lowest (12.6% fat and 16.0% protein). It's as if the heat forced the fish to burn through their own body reserves just to survive. Even their shape changed: the fish in the hottest water became shorter and stockier, a sign of stress that could make them less valuable to fishmongers.
So, what's the takeaway? The paper suggests that while gilthead seabream can handle temperatures up to 28°C without too much trouble, pushing them to 32°C is a recipe for poor growth and wasted feed. The researchers calculated that the absolute best temperature for these fish to grow is around 25.9°C, and the best temperature for them to eat efficiently is around 24.4°C. Since the Red Sea gets much hotter than this in the summer, especially in the southern regions where temperatures can hit 31–33°C, the paper suggests that fish farmers should be careful about where they put their cages. They might want to stick to the cooler northern parts of the Red Sea to avoid the "heat stress" that turns a thriving fish farm into a struggling one. The fish aren't just getting hot; they're getting hungry, tired, and small, proving that in the ocean, as in life, sometimes you just need to cool down to get ahead.
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