Fish are masters of reproductive resilience.
About 450 species switch sexes over their lifetimes to maximize their number of offspring. The fish do so by undergoing hormonal changes that transform their organs from those of one sex to the other. Patterns of sex switching vary by species. Big females produce more eggs than little females, so for some species, such as clownfish, it's best to be a male early in life when more runty and then switch to a female later on. But among males that fight each other for females or territories—such as groupers, sea breams (pictured), and porgies—being a too-small male can mean no offspring at all. In that case, it's better to stay a small female instead.
Now, this age-old strategy is allowing fish like the sea bream to adapt to a modern challenge that also disrupts the sex balance: overfishing. Fishers favor the biggest catch. Because one sex is usually bigger than the other, the bigger sex risks being fished out. But researchers have found that sea breams—flavorful, reddish fish common in warmer Atlantic Ocean coastal waters—are ready. Removing big males prompts earlier-than-usual sex changes in some females, so the sex balance is preserved. Still, it's more a short-term strategy than a long-term solution, researchers say. The fish are switching sex at younger ages, so females don't have a chance to grow big. That trend translates into fewer offspring and a shrinking population. That resilience strategy keeps them reproducing for now—but the fish can't save themselves all on their own.
Source: Science, Author - Elizabeth Pennisi