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External Morphology of Labeo rohita | Rohu | Diagram

In this article, we will learn about the external morphology of Labeo rohita or rohu fish. Labeo rohita is a very common fish in South Asia, especially in India, Bangladesh, and Myanmar. It is a carp fish and it has so much demand in the local market because of its taste. The common name of Labeo rohita is Rohu / Rui. The term external morphology of Rohu, the external structure of Rohu or the external features of Rohu are similar.

Systematic Position / Classification

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

Habit and Habitat of Labeo rohita

  • Rohu is an herbivorous fish species.
  • Its chief food is various phytoplankton, zooplankton, and aquatic plants.
  • It is a fast-growing fish species that can attain a maximum length of up to 1.5 meters and a weight of up to 25 kg.
  • Rohu is a diurnal fish species that is active during the day and rests at night.
  • Rohu is a bottom-dwelling fish species that is typically found in freshwater habitats with slow to moderate water flow.
  • It prefers deep pools and runs of rivers, and can also be found in lakes, ponds, and reservoirs.
  • Rohu is tolerant to a wide range of water conditions, including temperatures ranging from 25°C to 32°C, pH ranging from 6.5 to 8.5, and dissolved oxygen levels ranging from 3 to 6 ppm.

Labeo rohita (Rohu) Labeled Diagram

Labeled diagram of Labeo rohita or Rohu

Fig: External morphology of Rohu/Rui

External Morphology of Labeo rohita (Rohu)

1. Shape, Size, and Color

      • Spindle-shaped body. 
      • The color is greyish or blackish on the back, and silvery-white or pale on the two sides and belly.
      • Full-grown individual measures 1 meter in length.
      • A full-grown individual measures 20 – 25 kg in weight.
      • The body is divided into a head, trunk, and tail.

2. Head

      • The Head extends from the tip of the snout to the hind edge of the operculum.
      • The snout is depressed, short, and obtuse.
      • A pair of external nostrils are present on the dorsal surface of the snout. 
      • The mouth is subterminal; it is the large transverse aperture, bounded by thick and fleshy lips.
      • Two small, thread-like, sensory maxillary barbels are present at the corners of the mouth. Rostral barbels are absent.
      • Teeth and tongue are lacking.
      • The eyes are large and located on each lateral side of the head.
      • The eyes on the head are without eyelids but are protected by a transparent protective membrane.
      • Behind the eye, on either side, there is a large movable bony gill cover or operculum present. 
      • The branchiostegal membrane is attached to each operculum posteriorly.
      • Beneath each operculum, there are four comb-like gills in a branchial/gill chamber.

3. Trunk

      • It is the thick middle part of the body.
      • The trunk is elongated and oval in cross-section.
      • It is wide in the middle and narrow towards the dorsal and ventral sides.
      • It is covered over by thin, overlapping cycloid scales.
      • On either side of the trunk extending from the back of the operculum up to the tail, there is a dark line on the mid-ventral portion of the body called, the lateral line.
      • Fins are well-developed and supported by bony fin rays.
      • In the trunk region, there found three kinds of fins e.g. dorsal fins, pectoral fins, and pelvic fins. 
      • On the back of the middle of the trunk, there is a single large somewhat rhomboidal fin called the dorsal fin.
      • Just behind the operculum, there is a pair of fins on either side of the body called the pectoral fins.
      • Behind the pectoral fins, on the ventral side of the trunk, there is a pair of fins on either side called pelvic fins.
      • Three kinds of apertures are found in the trunk region. They are found mid-ventrally at the posterior end of the trunk. The anterior aperture is the anus, the middle is the genital, and the posterior is the urinary aperture.

4. Tail

      • It comprises about one-third posterior part of the body.
      • It is laterally compressed and narrower behind.
      • At the end of the tail, there is a large caudal fin.
      • On the ventral side of the tail region, there is a median anal fin lying just posterior to the urinary aperture.
      • The tail is the principal locomotor organ.

Frequently Asked Questions (FAQs)

1. Do teeth and tongue present in Labeo rohita?

Ans: No, teeth and tongue are lacking in Labeo rohita.

2. Do eyelids present in the eyes of Labeo rohita?

Ans: No. The eyes on the head are without eyelids but are protected by a transparent protective membrane.

 

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