Rohu (Labeo rohita)

Rohu (Labeo rohita) is a major freshwater fish species widely cultivated and consumed across South and Southeast Asia. Belonging to the family Cyprinidae, it is one of the three principal species used in Indian polyculture systems, alongside Catla catla and Cirrhinus mrigala. Known for its economic value, nutritional richness, and cultural significance, Rohu holds an eminent position in inland fisheries and aquaculture practices throughout the Indian subcontinent.

Taxonomy and Classification

Rohu is a cyprinid fish, belonging to the order Cypriniformes, which comprises carps and minnows. Its scientific classification is as follows:

• Kingdom: Animalia
• Phylum: Chordata
• Class: Actinopterygii
• Order: Cypriniformes
• Family: Cyprinidae
• Genus: Labeo
• Species: Labeo rohita

The species was first described by Hamilton in 1822. It is sometimes colloquially referred to as “Rui” in Bengali, “Rohu” in Hindi, and by similar names across regional languages of India and Bangladesh.

Morphological Characteristics

Rohu is a large-sized fish with a typical carp-like appearance. Its body is elongated, laterally compressed, and covered with large cycloid scales. The dorsal profile is slightly arched, and the head is relatively small with a terminal mouth adapted for column feeding.
Key identifying features include:

• Colouration: Bluish or dark grey on the dorsal side, silvery on the flanks, and whitish on the ventral region.
• Fins: The dorsal fin originates near the pelvic fin and contains 12–13 branched rays. The pectoral, pelvic, and anal fins are reddish or orange in adults.
• Size: Rohu can attain a length of up to 100 cm and a weight exceeding 20 kg under optimal conditions.
• Lips: Thick and fringed, enabling the fish to graze on periphyton and detritus.

Natural Habitat and Distribution

Rohu is a riverine species native to the Ganges, Brahmaputra, and Indus river systems. It thrives in freshwater environments such as rivers, ponds, lakes, and floodplains. The species prefers tropical and subtropical climates, flourishing in water temperatures between 14°C and 38°C.
The natural distribution of Labeo rohita extends across India, Nepal, Bangladesh, Pakistan, and Myanmar, with introductions into other Asian countries like Thailand and Indonesia for aquaculture. In India, it is particularly abundant in the eastern and northern regions, especially in the states of West Bengal, Bihar, Assam, and Uttar Pradesh.

Feeding and Behaviour

Rohu is an omnivorous column feeder, meaning it primarily feeds in the middle layers of the water column. The diet includes:

• Phytoplankton and zooplankton
• Decaying organic matter
• Aquatic vegetation and algae
• Small crustaceans

Larval and juvenile stages are mostly zooplanktivorous, while adults shift towards a more herbivorous diet. The fish exhibits a gregarious nature and often forms schools, especially during migratory or breeding movements.

Reproduction and Life Cycle

Breeding in Rohu is seasonal, typically coinciding with the monsoon months of June to August. In natural riverine environments, the species migrates upstream to shallow inundated areas with slow-moving water for spawning. Fertilisation is external, and females can produce up to 0.3 to 0.5 million eggs per kg of body weight.
In aquaculture, induced breeding using pituitary gland extract or synthetic hormones has revolutionised Rohu seed production. Hatchery-bred fry and fingerlings are now extensively used for pond culture, ensuring uniform quality and year-round availability.

Aquaculture and Farming Practices

Rohu is one of the three main species in Indian major carp polyculture, often cultivated together with Catla catla and Cirrhinus mrigala due to their complementary feeding habits. Rohu occupies the middle column of the pond, Catla the surface, and Mrigal the bottom layer, thereby maximising resource utilisation.
Culture methods include:

• Pond preparation: Liming and fertilisation of ponds to promote plankton growth.
• Stocking density: Typically 4000–10000 fingerlings per hectare.
• Feeding: Application of formulated or farm-made feed containing rice bran, mustard oil cake, and other protein sources.
• Growth period: Marketable size (1–1.5 kg) is achieved in 10–12 months under optimal conditions.
• Harvesting: Partial or complete harvesting is done using drag nets or seine nets.

The species is now farmed extensively under semi-intensive and intensive systems, contributing significantly to the total freshwater fish production in India and Bangladesh.

Economic and Nutritional Importance

Rohu is a commercially valuable species, forming a cornerstone of inland fish markets. It commands high consumer demand due to its flavour, tender texture, and nutritional value.
Economic importance:

• Supports rural livelihoods and employment through aquaculture, marketing, and processing.
• Contributes a substantial portion of India’s inland fish export and domestic consumption.
• Plays a role in food security in South Asia.

Nutritional composition (per 100 g edible portion):

• Protein: 17–20 g
• Fat: 2–5 g
• Minerals: Rich in calcium, phosphorus, and iron
• Omega-3 fatty acids: Present in moderate amounts
• Energy value: Approximately 110–120 kcal

These attributes make Rohu an essential component of a balanced diet, particularly in regions where fish is a staple protein source.

Role in Ecosystems and Environmental Significance

Rohu contributes to the ecological balance of freshwater ecosystems by controlling plankton populations and promoting nutrient cycling. Its feeding habits help in maintaining the biological productivity of water bodies. Moreover, the use of Rohu in integrated aquaculture systems, such as rice–fish farming, enhances resource efficiency and sustainable agricultural output.

Challenges and Conservation

Despite its economic success, Rohu populations face challenges from habitat degradation, pollution, and overfishing. Loss of breeding grounds due to river damming and siltation has reduced natural recruitment in several rivers. Aquaculture practices sometimes encounter issues such as:

• Water quality deterioration
• Disease outbreaks (notably Epizootic Ulcerative Syndrome)
• Genetic erosion from inbreeding in hatchery stocks

Conservation efforts include the development of genetically improved strains, establishment of brood banks, and implementation of sustainable aquaculture practices to preserve genetic diversity and enhance productivity.

Cultural and Culinary Significance

Rohu holds considerable cultural and culinary value across South Asia. It features prominently in traditional cuisines, particularly in Bengali, Odia, and Assamese households. Popular dishes include Rohu Kalia (spiced fish curry), Rui Maach Bhaja (fried Rohu), and Rohu Jhol (light fish stew). In Hindu traditions, Rohu is often considered auspicious and used in ceremonial feasts and rituals.
In Bangladesh and parts of eastern India, Rohu is also a symbol of prosperity and is frequently presented as a gift during weddings and festivals.