PRACTICAL ON THE GILLS OF A TILAPIA
PRACTICAL ON THE GILLS OF A TILAPIA
#01
Cut the specimen transversely along the anterior point of attachment of the pelvic fin and discard the tail end portion. Carefully cut and remove the operculum on one side of the other portion with a sharp knife
Make a drawing 8-10cm long of the side of the specimen from head to mid trunk, from the side from which the operculum has been removed.
Detail of drawing.
- Cut edge of operculum shown with double lines
- Not less than 5 backwardly overlapping scales
- Shape of Gill rakers shown
- Mouth with double lines
Give the functions of each structure observed in the specimen.
- Gill bar/arc: support the filament and rakers
- Gill filaments: gaseous exchange.
- Gill rakers: strain food and direct it into the oesophagus
Describe the adaptation of the organ to its function.
- Presence of filaments, which provides a large surface area for gaseous exchange
- Filaments are highly vascularized (with a dense capillary network) to facilitate the transport of gases.
- The thin walls of the filament provide high permeability, allowing for easy diffusion of gases.
- Interlocking gill rakers to strain food in water.
Describe the features observed in the specimen that make it difficult for predators to detect it in its environment.
- 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
What name is given to the phenomenon described in (d)(i) above
- Countershading
Name any four sensory organs:
- Eyes detect light
- Nostrils for smell
- Skin for touch
- Lateral line for vibration
Name the structure that directs food into the oesophagus
- Gill rakers
#02
Specimen: Gill of a bony fish in a petri dish
Habitat of the organism from which the specimen is obtained
- pond
- river
- lagoon
- streams
- lakes
Adaptive features of the specimen
- Presence of filaments, which provides a large surface area for gaseous exchange
- Filaments are highly vascularized (with a dense capillary network) to facilitate the transport of gases.
- The thin walls of the filament provide high permeability, allowing for easy diffusion of gases.
- Interlocking gill rakers to strain food in water.
Adaptation for gaseous exchange
- Presence of filaments, which provide a large surface area for gaseous exchange
- Filaments are highly vascularised (high capillary network) to facilitate the transport of gases.
- Thin walls of filament provide high permeability for easy diffusion of gases.
Adaptation to feeding
- Interlocking gill rakers to strain food in water
Two functions of the specimen
- Gaseous exchange,
- Feeding,
- Osmoregulation
Give reasons for each function
Gaseous exchange
- Presence of gill filaments for gaseous exchange
Feeding
- Presence of gill rakers for straining food in water
Osmoregulation
- Presence of gill filaments to excrete excess salts
Level of organisation of the specimen
- Organ
The system in which the specimen is found
- Respiratory system
- Digestive system
Draw 8-10cm long of the specimen.
