Structure, Life Processes and Adaptation of Fish (Tilapia)

Objectives       

This  blog post provides readers with the following objectives. The reader will be able to:
o   Describe the external features of Tilapia 
o   Discuss the adaptation of Tilapia to its habitat.

bony fishes

FISH

There are two main groups of fish, bony fish (Osteichthyes) and cartilaginous fish (Chondrichthyes). The skeletons of Osteichthyes are made of bone e.g., Tilapia, goldfish, tuna, while the Chondrichthyes have cartilaginous skeletons e.g., sharks, rays and dogfish. Fishes are poikilothermic or ectothermic (cold-blooded) meaning; their body temperature depends on the temperature of their environment.


Tilapia sp.

Phylum: Chordata
Sub-phylum: Vertebrata
Class: Osteichthyes


Habitat of Tilapia

Tilapia is freshwater bony fish found in lakes, ponds, rivers and lagoons.


Structure of a Tilapia

The body has a rounded head and a trunk which tapers to the tail. This gives the fish a streamlined shape which enables it to move smoothly through the water.

The skin is covered with flattened, discoid overlapping scales.

It has wide terminal mouth and small sharp teeth. The pair of nostrils above the mouth helps the fish to smell food. It plays no part in breathing.

It has operculum (or gill cover) at each side of the head which covers the gills. It plays an important part in the breathing mechanism.

The lateral line is a clear line or tube that runs along each side of the body, behind the head to the tail. It is found just beneath the skin. It is filled with a jelly like liquid and has sensory nerve endings. It detects vibrations in the water or pressure changes enabling the fish to escape from enemies.

It bears fins at various points on the body. 

It has in its body cavity a long air filled bladder (swim bladder) just beneath the backbone. The swim bladder makes a fish buoyant. It enables the fish to move up and down in the water without swimming. Gases diffuse from the blood into the bladder to inflate it, rendering the fish less dense and when deflated the fish becomes more dense.

labelled drawing of a fish


Types of fish fins

a. Unpaired fins or median fins: are the dorsal fin, the ventral fin or anal fin and the caudal or tail fin. They control yawing and rolling movement.

b. Paired fins: are the pectoral fins and the pelvic fins. They are used for steering, balancing, braking and diving. They are also used to control pitching.


Nutrition in fish

Tilapia feeds on minute aquatic plants e.g., planktons and animals e.g., mosquito larvae and aquatic protoctist. 

Water containing food is taken into the mouth. As it flows through the slender projections called the gill rakers, it prevents the food particle from escaping.

The food then moves into the pharynx behind the buccal cavity and it is swallowed. This is filter feeding.


Excretion in fish

Ammonia is the nitrogenous waste substance excreted. Other excretory substances are excess salts and water. These are excreted by the kidney in urine. Carbon dioxide is excreted by diffusion out of the body through the gills.


Respiration in fish

Structure of the Gill

The gills are the organs of gaseous exchange. Each gill chamber contains four gills. Each gill is made up of two rows of red, soft and slender structures called gill filaments. Each row of the filament is attached to a bony bar called the gill bar or gill arch.


Adaptation of Filaments for Gaseous Exchange

o They have a large surface area.

o   They are well supplied with blood. 

o   They are thin walled to enable rapid diffuse into the blood.


Gaseous Exchange in fish 

gills of tilapia

During gaseous exchange, the mouth opens to take in water containing dissolved oxygen, whiles the operculum is pressed to the head.  As water enters the gill chamber, the mouth closes and floor of the mouth is raised, building up pressure in the mouth. The pressure forces the water to flow over the oil filaments, oxygen in the water diffuses into the blood capillaries of the filaments. At the same time, carbon dioxide in the capillaries diffuses into the water. Oxygen in the blood stream is carried to various parts of the body for tissue respiration.



diagram of lateral line and breathing system of fish

Movement in Fish

Tilapia moves in water by swimming. Rapid forward movement is brought about by the side-to-side lashing of the tail. This is controlled by the contraction of the muscle blocks on both sides of the flexible vertebral column. They are well developed especially in the tail region. The caudal fin also works with the paired fins in steering the fish through the water. During rapid movement, the paired fins are held close to the body and when extended, they slow down or stop the fish.

o The unpaired fins control yawing (the tendency of the body to zigzag from side-to-side. They also control rolling (rotation of the body around its longitudinal axis).

o The paired fins control pitching (tendency of the head to rise and fall).

The air or swim bladder enables up and down movement in the water without swimming. Gases diffuse from the blood into the bladder to inflate it, rendering the fish less dense and can rise easily. When deflated the fish becomes denser and sinks.

movement in fishes
These images are credited to D G Mackean www.biology-resources.com

Reproduction

Usually, the females lay eggs and the male shed the sperms into the water. The sperms swim to the eggs and fertilize them (external fertilization).

The fertilized eggs 
are abandoned by the parents and most are eaten by predators.

Certain species of Tilapia exhibit some degree of parental care and therefore called mouth brooders.

The male and female dig a shallow pit in the bed of the pond or lake. The female lays eggs and the male sheds sperms over them. 

The male then carries the fertilized eggs in his mouth for about two weeks until they hatch into tiny fish called fry. The fry retreat into the parent mouth when there is danger.


Structural Adaptations of the Fish

Tilapia fish have developed a range of structural adaptations that allow them to thrive in diverse aquatic environments. These adaptations enhance their survival, feeding efficiency, reproduction, and overall fitness in both natural and controlled habitats. Here are some key structural adaptations of tilapia:

1. Body Shape and Size

  • Laterally Compressed Body: Tilapia have a laterally compressed (flattened) body, which reduces water resistance and enhances maneuverability. This body shape is beneficial for navigating through various aquatic environments, including shallow waters and areas with dense vegetation .
  • Streamlined Profile: The streamlined body reduces drag, making tilapia efficient swimmers. This adaptation is crucial for escaping predators and foraging for food .

2. Fins

  • Dorsal Fins: Tilapia have two dorsal fins—the first dorsal fin has spiny rays that provide protection against predators, while the second dorsal fin is softer and aids in stability during swimming .
  • Pectoral and Pelvic Fins: These paired fins help with balance, steering, and braking. They are also used to maintain position in currents and for precise movements in complex environments .
  • Anal Fin: Positioned on the underside of the fish, the anal fin assists in stabilization and directional control.
  • Caudal Fin (Tail): The caudal fin is typically forked, providing powerful propulsion for swimming. The shape of the caudal fin can vary among species, influencing their swimming speed and maneuverability .

3. Gills and Respiratory System

  • Gills: Tilapia have well-developed gills covered by an operculum (gill cover). The gills are adapted to efficiently extract oxygen from water, even in low-oxygen environments. The large surface area of the gills allows for maximum oxygen exchange .
  • Air-Breathing Structures: Some species of tilapia possess air-breathing adaptations, such as modified gill structures or labyrinth organs, which allow them to survive in oxygen-poor water by gulping air from the surface .

4. Mouth and Feeding Adaptations

  • Mouth Structure: Tilapia have a versatile mouth structure that allows them to feed on a wide range of food sources, including plants, algae, small invertebrates, and detritus. The mouth can be protrusible, enabling them to extend it to capture prey or food particles .
  • Pharyngeal Teeth: Tilapia possess specialized teeth located in the throat, known as pharyngeal teeth, which help grind and process food. This adaptation is particularly useful for crushing hard food items, such as mollusks or plant material .

5. Lateral Line System

  • Lateral Line: Tilapia have a lateral line system, a sensory organ that runs along the sides of their body. This system detects vibrations and changes in water pressure, helping tilapia sense the presence of predators, prey, and obstacles. It is also crucial for schooling behavior and navigation in murky waters .

6. Scales and Skin

  • Ctenoid Scales: Tilapia are covered in ctenoid scales, which are rough and have tiny teeth-like projections. These scales provide protection against physical damage and parasites. They also reduce friction, aiding in smooth swimming .
  • Mucous Coating: The skin is covered in a mucous layer that protects against infections and parasites. This mucous coating also reduces drag, enhancing swimming efficiency .

7. Coloration and Camouflage

  • Coloration: Tilapia exhibit a range of color patterns, which can serve various functions, including camouflage, communication, and mate attraction. Coloration can vary between species, sexes, and even environmental conditions .
  • Camouflage: The coloration and patterns on tilapia can help them blend into their surroundings, making it more difficult for predators to spot them. Some species can also change their coloration slightly to match their environment better .

8. Reproductive Adaptations

  • Mouthbrooding: Many tilapia species exhibit mouthbrooding behavior, where one of the parents (usually the female) carries fertilized eggs and young fry in their mouth. This adaptation provides protection to the offspring during their vulnerable early stages of life .
  • Nest Building: Male tilapia often build and guard nests where females lay their eggs. This behavior helps ensure the survival of the next generation by providing a secure place for the eggs to develop .

These structural adaptations enable tilapia to survive and thrive in various environments, making them a highly successful and versatile group of fish. These adaptations also contribute to their popularity in aquaculture, as they can tolerate a wide range of conditions and are relatively easy to farm.


Conclusion

Understanding the structure and life processes of tilapia provides valuable insights into their biology, behavior, and aquaculture management. Their anatomical features, feeding habits, reproductive strategies, and environmental adaptations make them a versatile and important species in both natural and aquaculture systems.

References

  1. FAO - Tilapia Aquaculture
  2. Aquaculture Network - Tilapia Biology
  3. Science Direct - Tilapia Growth and Development
  4. National Center for Biotechnology Information - Tilapia Reproduction

This comprehensive overview covers the critical aspects of tilapia biology and their importance in aquaculture and natural ecosystems.



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