The rohu is a type of carp that is native to the rivers of India and other Asian regions, and has also been introduced with relative success into rivers and lakes in Japan, the Philippines, and some African countries. This fish is extremely important to the commercial fishing industry in India. The scientific name for the rohu is Labeo rohita.
Also called a rui, the rohu can reach a maximum length of 78.7 inches (200 cm) and weight as much as 99 pounds (45 kg). These fish have blue or black scales on their backs and lighter, silvery scales on their bellies. They have a single dorsal fin, as well as two pectoral and anal fins, and a forked caudal fin, or tail. Their mouths are small and their heads have no scales.
A solitary species, the rohu lives and feeds alone. Primarily active in daylight, these fish are largely column feeders, eating mostly algae and other aquatic vegetation. They are eurythermal, meaning they can tolerate changes in water temperature, but need water warmer than 57.2°F (14°C) to survive.
During monsoon season from April to September, the rohu spawns. Moving to shallow parts of flooded rivers, females lay 266,000 to 2,794,000 eggs, depending on the individual female's size. Temperatures ideal for spawning, 71.6–87.8°F (22–31°C), are significantly higher than the minimum temperature that these fish can normally tolerate.
Juvenile fish eat primarily zooplankton and may swim in schools while feeding until reaching adulthood. Rohu are fast growing, attaining 13.7–17.7 inches (35–45 cm) in length and 24.6–28.2 ounces (700–800 g) within their first year. These fish do not live longer than ten years.
The Rohu is the most important species of carp in the commercial fishing industry in India because of its low maintenance cost and high market value. Though most eggs, or seeds, are produced artificially in the fisheries themselves, seeds are also collected from rivers to use in the hatcheries. Fish are usually sold fresh in local markets, but many are put on ice and shipped by truck to places as far as 1,243–1,864 miles (2,000–3,000 km) away. The iced fish, however, have a lower market value than then fresh.
Ideally fish are grown in ponds with organic methods and materials, so in theory, these hatcheries are environmentally friendly. Unfortunately, poor practices, such as overstocking ponds to produce more fish, lead to disease and the increased use of environmentally unfriendly pesticides in some hatcheries. In these non-ideal hatcheries particularly, rohu are susceptible to many types of bacterial, fungi, and parasitic diseases.