Sturgeons are late-maturing fish with distinctive features such as a heterocercal caudal fin similar to that of sharks and an elongated, spindle-like body with smooth skin, no scales, and five lateral rows of bony plates called scutes. Several species can grow to be very tall, with average lengths of 7–12 feet. A beluga female caught in the Volga measured 7.2 m (24 ft) long and weighed 1,571 kg, making her the world's largest sturgeon (3,463 lb). Sturgeons are bottom-fed anadromous fish that migrate upstream to spawn but spend the majority of their lives feeding in river deltas and estuaries. Some animals only live in freshwater, while others prefer to live in marine habitats near coastal areas and have been known to venture out into the open ocean.
The roe of many species of sturgeon is harvested and processed into the high-end food caviar. This has resulted in widespread overexploitation, which, when combined with other conservation challenges, has pushed most of the species to critically endangered status, putting them on the verge of extinction.
Sturgeons are slow-maturing fish with a long lifespan. Their average lifespan is 50 to 60 years, and they do not have their first spawn until they are 15 to 20 years old. Since they need special conditions, sturgeons are broadcast spawners and do not spawn every year. Due to varying environmental conditions, such as the proper photoperiod in spring, clear water with shallow rock or gravel substrate where the eggs may cling, and proper water temperature and flow for oxygenation of the eggs, those requirements may or may not be met every year. Although a single female will produce 100,000 to 3 million eggs, not all of them will be fertilized. When the fertilized eggs come into contact with the bottom substrate, they become sticky and stick to it. The embryos take eight to fifteen days to develop into larval fish. They are fully reliant on their yolk sacs for nutrition during this period. The larvae are carried downstream by river currents into backwater areas including oxbows and sloughs, where the free-swimming fry feed on insect larvae and crustacea for their first year. They attain 18 to 20 cm (7.1 to 7.9 in) in length during their first year of development and migrate back into the swift-flowing currents of the main stem river.
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