2. 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.
3. INTRODUCTION
Fishes 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.
4. MATERIALS ANDMETHODS
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
8. RESULT
The morphological characteristics of the alimentary canal observed in the
three fishes are followed.
Sardinella longiceps
It 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.
10. Thunnus obesus
Tunas 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.
12. 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.
15. 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
16. 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.}.
17. The graphshowing the R.LGvalue of three fishes.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Herbivore Carnivore Omnivore
Sardinella longiceps Thunnus obesus Rastrelliger kanagurta
{R.L.G}
{R.L.G}
18. 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.
19. 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.
