We’re eating more fish than ever these days. At around 20 kilograms per person global fish consumption is now more than twice what it was in the 1960s. What’s really remarkable, though, is where that fish comes from.

        For the first time in human history, most of our aquatic (水产的) food now comes from farming rather than fishing.

        People ate around 73 million tonnes of farmed fish—just more than half of the volume of fish that humans consumed—in 2014. That’s out of a total fish supply of 167 million tonnes; the remaining 20 million or so tonnes go into things like animal feed and medical products.

        To keep eating fish at the current rate, we’re definitely going to need to keep aquaculture (水产养殖) developing. That’s because the volume of fish caught in the wild has leveled off since the 1990s.

        Back in 1974, only 10% of marine fish stocks had been overfished. Now, more than three-tenths are. Only a tenth of our oceans’ fish stocks could sustain heavier fishing than current levels.

        But while catchings at sea have suffered, fish-farming has been growing at a fast rate. A lot ofthat is coming from China, which produces 60% of the world’s farmed fish. In fact, some 35 countries, including China, now produce more farmed than wild-caught fish.

        This shift toward aquaculture isn’t just good for ensuring salmon (三文鱼) on your plate; it’s also crucial to ensuring food security and sustainability. By 2050, the world will need to feed an estimated 9.7 billion people. They’ll have to get their protein somewhere. However, raising cattle, pigs, and other land-based animals requires vast sums of grain and water. For example, pound for pound, beef requires 15 times more feed to raise than carp, a freshwater fish farmed all over Asia. That grain—and the water needed to grow it—could be consumed by people instead.

        However, aquaculture is no silver bullet. In some southeast Asian countries, shrimp farming does disastrous damage to marine ecosystems. Despite these problems, however, shrimp continues to be among the most popular seafoods worldwide.

解析：A。题干中问为什么作者认为水产养殖很重要，原文倒数第二段讲到了转而发展水产养殖的好处，包括能保证粮食安全和可持续性，因为到2050年，全世界将需要养活大约97亿人。由此可知，水产养殖的重要意义在于养活世界上不断增加的人口，故正确答案为A。

错项排除：原文中只暗示说鱼类可以作为人类摄取蛋白质的一个途径，但并没有说是可靠的蛋白质来源，故排除B项。C项的maintaining both mental and physical health和D项的a balanced healthy diet在原文中无依据，故均可排除。