Fish tales: Six amazing journeys to celebrate World Fish Migration Day

Tomorrow, April 21, marks World Fish Migration Day. Many animal species make lengthy migrations as one-time or annual portions of their life cycle. Whereas journeys by birds between North and South America and large mammals across Africa’s Serengeti are highly visible, the migrations of countless fish, often over great distances and across disparate habitats, go on largely hidden from view. The impetuses for fish to swim long distances are manifold, among them, differences in food availability, water levels, temperatures, spawning habitat, and vulnerability of their young to predation. A noteworthy category of fish migration is diadromy, the movement between fresh and salt waters. Anadromous fish spawn in freshwaters and go to sea, whereas catadromous species spawn in the sea but live most of their lives in fresh waters. Most anadromous species “home” to the rivers they were born in to mate; catadromous species reproduce in the same general marine waters where they originated. But many other fish make long excursions within either fresh or salt waters: along vast reaches of the Amazon and other large rivers, or across immense swaths of ocean. Healthy fish stocks with unimpeded migrations are essential to feeding humankind and maintaining the ecological equilibrium of the world’s waters. But fish migrations are being increasingly stressed by a worldwide boom in the building of dams that block their essential riverine passage, pollution, overfishing, lowering of water levels for agriculture and drinking water, and climate change. This year marks the third World Fish Migration Day, a biennial happening…

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