PRACTICAL NOTE ON TILAPIA (BONY FISH)
PRACTICAL NOTE ON TILAPIA (BONY FISH)
Habitat:
- Pond,
- lake,
- lagoon
- streams
- estuarine
Reasons for habitat:
- Possession of fins
- Possession of gills
- Presence of opercula
- Streamlined body
Mode of reproduction:
- Sexual/oviparous/external fertilization, with parental care
Biological Classification of Bony Fish
Phylum Chordata
Reasons
- Presence of notochord
- Presence of a dorsal hollow nerve cord
- Presence of pharyngeal slits
- Presence of post anal tail. This means a tail extends beyond the anus
- Presence of bilateral symmetry
- Presence of well-developed sense organs
Class Osteichthyes
- Presence of a bony skeleton
- Presence of cycloid scales (flat, backwardly overlapping, removable scales).
- Presence of the terminal mouth
- Presence of bony fins (fins strengthened by bony fin rays)
- Presence of a homocercal tail
- Presence of operculum
Observable Features in Tilapia
- Presence of operculum
- Presence of fins
- Presence of a tail fin
- Presence of eyes
- Presence of the nostril
- Presence of backwardly overlapping scales
- Presence of lateral line
- Presence of the terminal mouth
Other examples in the same Class
Any good example of bony fish, such as;
- Tuna,
- mudfish,
- herring,
- salmon etc
Features on the head of the bony fish
- Eyes
- Nostrils
- Mouth
- Operculum
Features on the trunk of the bony fish
- Dorsal fin
- Pectoral fins
- Pelvic fins
- Anal fins
- Anus
Features on the lateral side of the bony fish
- Pectoral fins
- Lateral line
- Operculum
- Eyes
Features in the median region of the bony fish
Medial is close to the main axis (midline). Lateral is further away from the midline
- Anal fin
- Caudal fin
- Dorsal fin
- Mouth
- Anus
Features of Evolutionary Significance in Tilapia
- Gills for gaseous exchange in water
- Fins for swimming in water
- Presence of caudal fin/tail
Adaptive features in Tilapia
- Gills for gaseous exchange
- Fins for swimming, balancing, and steering
- Backwardly overlapping scales to facilitate forward movement. (Scales for protection and streamlined effect)
- Streamlined body facilitates swimming in water
- Dark dorsal and light ventral colours to blend with the environment.
- Lateral line detects vibrations and pressure changes in water
- Gill slits allow water to flow backward to propel the animal forward
- Operculum to protect the gills and also help in gaseous exchange and feeding.
- Eyes large and laterally placed for wide vision
- Nostril for smell to escape dangers
- Wide mouth for feeding and respiration
Features for movement
- Streamlined shape provides reduced resistance in water
- Paired fins for steering, braking, and controlling pitching
- Median fins for balancing (controlling yawing)
- Tail fin for propulsion
- Backwardly overlapping scales provide movement with little resistance in water
- Swim bladder for buoyancy (not observable)
Features to escape danger
- The lateral line detects vibration in water
- Eyes are large and laterally placed for wide vision
- Fins to swim away from predators
- Nostril to smell danger
- Countershading provides camouflage against predators
What is Countershading?
- Different colouration of the dorsal and ventral sides.
- Dark dorsal side makes it difficult to be detected from above against a dark background below.
- Light ventral side makes it difficult to be detected from below against the light background of the sky above
Describe the features used for movement
Fins
- Paired fins (pectoral fins and pelvic fins) provide
- steering
- braking
- control of pitching (upward and downward movement) or the tendency of the head to rise and fall
Caudal fin provides
- forward force
- Steering
- Dorsal and anal fins (median fins)
- prevent rolling sideways
- prevent yawing (deviating from a straight course or zigzag movement)
Functions of the dorsal fin:
- balancing,
- stabilizing,
- prevents rolling
Sensory organs
- A pair of eyes (on the head) for vision
- Nostril (on the head) connected to the olfactory organ for smell
- Lateral line (on the trunk) for detecting vibration and pressure in water
- Skin is sensitive to touch (on the trunk)
Lateral line system:
- It consists of clusters of sensory cells that help to detect vibrations in water to detect enemies, food, and the direction of the water current.
State the functions of two observable features on the trunk of Tilapia
- Lateral line detects vibration in water
- Dark dorsal side makes it difficult to be detected from above against a dark background below
- Light ventral side makes it difficult to be detected from below against the light background of the sky above
- Dorsal, pelvic, pectoral, and anal fins for swimming and balancing
Mode of nutrition:
- Heterotrophic/Holozoic
Feeding habit:
- Omnivorous on larvae, crustaceans, molluscs, and water weeds
Diet:
- larvae,
- water weeds,
- crustaceans,
- molluscs
Method of feeding:
- Filter feeding
Reasons for the method of feeding:
- Presence of gill rakers
Adaptation to feeding:
- Wide mouth for trapping food
- Presence of gill rakers to strain food in water
- Presence of wide eyes to spot food
- Presence of nostrils to smell food
- Presence of operculum
- Ventilation movement to draw in water containing food
Description of filter feeding.
- The feeding method is known as filter feeding.
- It feeds on water weeds.
- Food passes into the mouth with water and then over the gills and out through the opercular opening.
- As water flows over the gills, food particles are filtered or strained in the gill rakers.
- The filtered food then moves into the pharynx for swallowing
- Diet: larvae, crustaceans, molluscs, water weeds
Equipment used to harvest Tilapia/bony fish
- Fishing net
- Hook and line
- Wicker work trap
Economic importance of Tilapia
- Source of food
- Source of employment
- Foreign exchange/income
- Biological control of mosquito larvae
- Food substances obtained from Tilapia
- Protein
- Vitamins
Methods to preserve Tilapia as food
- Salting
- Smoking
- Refrigerating
- Canning
- Drying
Human activities are threatening the population of Tilapia in water bodies
- Excessive fishing
- Use of poisonous chemicals in fishing
- Destruction of vegetation near water bodies
- Use of unauthorised fishing nets
Methods to conserve Tilapia/bony fish
- Ban fishing in some areas
- Ban fishing at certain periods of the year
- Avoid using poisonous chemicals in fishing
- Use authorised fishing net
