A COMPARITIVE STUDY ON THE MORPHOLOGICAL ADAPTATIONS OF
THE ALIMENTARY CANAL IN SARDINELLA LONGICEPS, THUNNUS
OBESUS, AND RASTRELLIGER KANAGURTA
ASHA SAMSupervising Teacher
Dr . SUNIL KUMAR
Dept :Of : Zoology
Catholicate college
OBJECTIVES OF THE STUDY
To compare the morphological adaptation of the alimentary canal in Sardinella longiceps,Thunnus obesus and Rastrelliger kanagurta.
To find the RLG value of three fishes.
INTRODUCTIONFishes are cold blooded gill-breathing , aquatic vertebrates, with
limbs represented by fins.
Fishes feed on a wide range of food material and obtain their
nourishment from plants as well as animals.
The food feeding habitat are related with the digestive system of
the fishes. Mainly alimentary canal structure varies in different
species of fishes.
And is generally adapted in relation to the food and feeding habits.
MATERIALS AND METHODS In the present study, three different species of marine fishes belonging to
the different food groups such as herbivore, carnivore, and omnivore were selected and there include Sardinella longiceps, Thunnus obesus, Rastrelliger kanagurta.
The fishes were selected based on the economic values and their availability throughout the year and their sizes of the three fishes were apt for dissection.
The fishes carefully dissected with scissors, needle etc. The fishes were also carefully measured for the total length, standard
length, total gut length, and mid width of the body. The Relative Length of Gut[RLG]was measured using the formula,
RLG= Length of alimentary canal
Standard length of fish
Fig 1: Sardinella longiceps
Fig 2:Thunnus obesus
Fig 3:Rastrelliger kankgurta
RESULT The morphological characteristics of the alimentary canal observed in the three
fishes are followed.
Sardinella longicepsIt is a herbivorous marine teleost which feeds mainly at night and may feed even
during day time.
Oropharynx: The mouth is narrow, palatal organs are well developed and minute pharyngeal
teeth is present.
Oesophagus: It is short and narrow and merges with the intestinal bulb with out demarcation.
Intestine: It is a long, thin walled and highly coiled in structure . The relative length of gut is
1.868.
Fig 4:Photograph showing uncoiled gut of Sardinella longiceps
Thunnus obesusTunas are highly carnivorous. They feeds mainly on smaller fishes , crabs ,larvae of prawns , marine organism etc.
Oropharynx:The mouth is large, like a grinning mouth. Lips are thin and hard .The upper and lower jaws are provided with teeth.
Oesophagus:It is long and distensible to facilitate swallowing of large prey. There is a small external constriction separating the oesophagus from the stomach.
Intestine:The intestine is small length forming just 2-3 coils .The relative length of gut is 0.272
Stomach:It has a true stomach and quite large It is nearly Y-shaped.
Fig 5:Photograph showing uncoiled gut of Thunnus obesus
Rastrelliger kanagurta Indian mackerel consisting of the phytoplankton and zooplankton. It
is a omnivore, feeding on algae ,aquatic plants , insects, micro crustaceans and larvae of prawn.
Oropharynx: Mouth is moderate and is bounded by soft, thin, unfringed lips.
Oesophagus: It is short and slight muscular in nature.
Intestine: Medium sized and it is thin walled and uniform diameter throughout
the length.The relative length of gut is 1.033.
Fig 6: Photograph showing uncoiled gut of Rastrelliger kanagurta.
Int-Intestine:Os-Oesophagus:St-Stomach:Rct-Rectum:Pyl.ca-Pyloric caecae.
Sardinella longiceps Thunnus obesus Rastrelliger kanagurta
Fig 7:Diagrammatic representation of the uncoiled guts of the 3fishes studied.
Table 1:Feeding habits and morphology of mouth parts of the three fishes.
SPECIES FEEDING MOUTH TEETH PALATAL
ORGANS
GILL
RAKERS
S. longiceps Herbivore Narrow,sub
terminal,
Minute Pharyngeal
teeth.
Well developed Closely set to
form a fine
sieve.
T.obesus Carnivore Mouth large
with wide gap.
Nearly21canines
present .
Poorly
developed
Long hard
teeth .
R.kanagurta Omnivore Moderate
Anterior , soft
thin un fringed
lips
Fine teeth are
Present.
Thick paiatal
organ
Short and
stumpy
NAME OF FISH FEEDING HABIT {R.L.G}
Sardinella longiceps Herbivore 1.868
Thunnus obesus Carnivore 0.278
Rastrelliger kanagurta Omnivore 1.033
Table 2: Comprehensive table showing feeding habit and Relative Length of Gut {R.L.G.}.
The graph showing the R.LG value of three fishes.
Herbivore Carnivore Omnivore Sardinella longiceps Thunnus obesus Rastrelliger kanagurta
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2 {R.L.G}
{R.L.G}
DISCUSSION
The structure of the alimentary canal varies in different species of fishes, is generally adopted in relation to the food and feeding habits.
The adaptations of the alimentary canal of fishes of their food are particularly evident in the form of mouth, size, shape and structure of the oropharynx, structure of the oesophagus , presence or absence and shape of stomach and the intestine and relative length of gut.
The short and nearly straight intestine is seen in carnivorous and predatory fishes, but long, thin walled and highly coiled in the herbivorous species . The omnivorous species show an intermediate condition.
The relative length of gut was highest in Sardinella longiceps1.868.It decreased to 1.033 for Rastrelliger kanagurta and the lowest , 0.272 was recorded for Thunnus obesus.
CONCLUSION
It can be concluded that of the three fishes studied, the Relative Length of Gut was highest in Sardinella longiceps1.868.It decreased to 1.033 for Rastrelliger kanagurta and the lowest, 0.272 was recorded for Thunnus obesus.
The morphological variations present in the structure of the alimentary canal being morphologically very well adapted to the mode of feeding of these three fishes. These adaptations are very important to a fish from the survival point of view.
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