MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF ...

UNIVERSITI PUTRA MALAYSIA
MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF
Pangasius nasutus FROM SG. PAHANG IN MARAN DISTRICT,
PAHANG, MALAYSIA
MOHD ZAFRI BIN HASSAN
FP 2006 17

MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF Pangasius
nasutus FROM SG. PAHANG IN MARAN DISTRICT, PAHANG, MALAYSIA
MOHD ZAFRI BIN HASSAN
MASTER OF SCIENCE
UNIVERSITI PUTRA MALAYSIA
2006

MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF Pangasius
nasutus FROM SG. PAHANG IN MARAN DISTRICT, PAHANG, MALAYSIA
By
MOHD ZAFRI BIN HASSAN
Thesis Submitted to the School of Graduate Studies, Universiti Putra
Malaysia in Fulfilment of Requirement for the Degree of Master of Science
November 2006

Specially dedicated to my beloved parents
ii

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in
fulfilment of the requirement for the Degree of Master of Science
MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF Pangasius
nasutus FROM SG. PAHANG IN MARAN DISTRICT, PAHANG, MALAYSIA
Chairman : Annie Christianus, PhD
By
MOHD ZAFRI BIN HASSAN
June 2006
Faculty
: Agriculture
The present study was conducted to describe the morphological differences
between P. nasutus and P. conchophilus, to describe and classify the histology
of oocyte and spermatogenic cells of mature P. nasutus and to observe the
seasonal patterns of the gonadal stages in twenty specimens of P. nasutus and
P. conchophilus from Maran. In order to signify the species differences, twenty
specimens of Thai-origin P. conchophilus from a cage culture at Sungai Pahang
near Pekan, Pahang, Malaysia were also examined. The morphometric
measurements were presented in percentage of standard length (%SL),
predorsal length (%PDL) and head length (%HL). Based on the classification
results, all P. nasutus specimens were different from P. conchophilus in both
populations, in terms of snout length, eye diameter, lower and upper jaw length.
A total of 205 P. nasutus were caught during the study period, from October 2004
to September 2005 for the gonadal stages study of P. nasutus. Nine distinctive
iii

oocytes stages observed in the study were from oogonia to late vitellogenesis.
Six microscopic oocytes developmental stages were assigned for the studied
ovaries of P. nasutus, namely resting, maturing, mature, spawning, running and
spent stages. Further, microscopic observation on the ‘whole-section’ of the
testes revealed that four testicular development stages could be distinguished
namely early spermatogenesis, spermatogenesis, maturation and spent stages.
In this study, it was found that the female and male P. nasutus were
reproductively active at the beginning of rainy season which commenced in the
middle quarter of 2005, from March to September coincided with the South-West
monsoon. The study also revealed that P. nasutus exhibits a single-modal
spawning season in a year, with multiple release of eggs during a single period.
Such condition showed that P. nasutus is a multiple-spawner as supported by the
group-synchronous oocyte development of the ovary. However, spawning did not
commence synchronously within the population with the obvious presence of
various female and male reproductive stages within a single sampling month.
iv

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai
memenuhi keperluan untuk Ijazah Master Sains
MORFOLOGI DAN PERINGKAT PERKEMBANGAN PEMBIAKAN Pangasius
nasutus DARI SG. PAHANG DI DALAM DAERAH MARAN, PAHANG,
MALAYSIA
Pengerusi : Annie Christianus, PhD
Oleh
MOHD ZAFRI BIN HASSAN
Jun 2006
Fakulti
: Pertanian
Kajian ini telah dijalankan untuk menerangkan perbezaan morfologi antara P.
nasutus dan P. conchophilus, menghurai dan mengkelaskan histologi oosit dan
sel-sel spermatogenik bagi P. nasutus matang dan seterusnya untuk melihat
corak bermusim untuk peringkat-peringkat gonad bagi P. nasutus. Dua puluh
spesimen P. nasutus dan P. conchophilus dari Maran, Pahang telah dikaji. Untuk
melihat perbezaan spesies, dua puluh spesimen P. conchophius berasal dari
Thailand tetapi dikultur dalam sangkar di Sungai Pahang, dekat Pekan, Pahang,
Malaysia, turut dikaji. Ukuran-ukuran morfometrik diberikan dalam bentuk
peratusan panjang piawai (%SL), panjang pra-dorsal (%PDL) dan panjang
kepala (%HL). Berdasarkan keputusan pengkelasan, semua specimen P.
nasutus adalah berbeza dari P. conchophilus pada kedua-dua populasi,
terutamanya dari segi panjang muncung, diameter mata, panjang rahang bawah
dan atas.
v

Sejumlah 205 spesimen P. nasutus ditangkap sepanjang waktu kajian yang
bermula dari Oktober 2004 sehingga September 2005. Sembilan peringkat
kematangan oosit telah diperhatikan dalam kajian ini adalah dari peringkat
oogonia sehingga peringkat akhir vitellogenesis. Enam peringkat perkembangan
oosit yang diperhatikan secara mikroskopik untuk keseluruhan ovari P. nasutus
dibahagikan kepada kepada peringkat rehat, sedang matang, matang, bersedia
untuk membiak, sedang membiak dan selesai membiak. Berdasarkan
pemerhatian mikroskopik bagi keseluruhan testis P. nasutus menunjukkan
terdapat empat peringkat perkembangan testis yang dapat dikenalpasti iaitu,
spermatogenesis awal, spermatogenesis, kematangan dan selepas pembiakan.
Kajian ini mendapati, betina dan jantan P. nasutus adalah aktif membiak pada
permulaan musim hujan yang bermula pada suku pertengahan tahun 2005, dari
Mac sehingga September serentak dengan musim monsun tenggara. Kajian ini
juga mendapati, P. nasutus mempunyai satu musim pembiakan khusus dalam
satu tahun, yang dapat dilihat dengan pelepasan telur yang berperingkatperingkat
pada sesuatu tempoh masa. Keadaan ini menunjukkan bahawa P.
nasutus merupakan pembiak yang melepaskan telurnya secara berperingkatperingkat
yang jelas dapat dilihat dari perkembangan oosit secara serentak
dalam dua atau tiga kumpulan di dalam satu-satu ovari. Walaubagaimanapun,
pembiakan tidak berlaku serentak di dalam populasi berdasarkan kehadiran
pelbagai peringkat perkembangan reproduktif betina dan jantan semasa
penyampelan di dalam satu-satu bulan.
vi

ACKNOWLEDGEMENTS
In the name of Allah, the Lord that I always put my belief in. Thanks to my
parents and siblings for being my pillars and strength all my life.
I would like to express my deepest gratitude to the chairman of my supervisory
committee, Dr. Annie Christianus for her tremendous encouragement, financial
assistance on the research expenses and camaraderie throughout the study
period. Not forgetting, many thanks to my co-supervisors Assoc. Prof. Dr. Siti
Shapor Siraj and Assoc. Prof. Dr. Siti Khalijah Daud for sharing their invaluable
expertise, ideas and comments on the research conducted and write-up. Thanks
to UPM for the scholarship and granting me study leave off my duty at UPM
Bintulu Campus.
The study could not have completed without the support and co-operations from
many parties, namely Assoc. Prof. Dr. Khir Bejo and his lab assistant Saipu for
allowing and helping me to use facilities in the Pathology Laboratory, Faculty of
Veterinary UPM; Assoc. Prof. Dr. Mohd Salleh Kamaruddin for his permission to
use Aquatic Biotechnology Laboratory, Faculty of Agriculture UPM, En. Jasni
Yusof at the UPM hatchery, En. Mat Piah and his family for their friendly
entertainment on the lodging and helping hands during sampling activities; and
last but not least, million thanks to my all-time friends Ikram, Sazahar, Halim and
Saufi to whom I owe their time and energy very much.
vii

I certify that an Examination Committee has met on 28 November 2006 to
conduct the final examination of Mohd Zafri Bin Hassan on his Master of Science
thesis entitled “Morphology and General Reproductive Stages of Pangasius
nasutus from Sg. Pahang in Maran District, Pahang, Malaysia” in accordance
with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti
Pertanian Malaysia (Higher Degree) Regulations 1981. The committee
recommends that the candidate be awarded the relevant degree. Members of the
Examination Committee are as follows:
Che Roos Saad, PhD
Associate Professor
Faculty of Agriculture
Universiti Putra Malaysia
(Chairman)
Sharr Azni Harmin, PhD
Associate Professor
Faculty of Agriculture
Universiti Putra Malaysia
(Internal Examiner)
Mustafa Kamal Abdul Satar, PhD
Lecturer
Faculty of Agriculture
Universiti Putra Malaysia
(Internal Examiner)
Mazlan Abdul Ghaffar, PhD
Associate Professor
Faculty of Science and Technology
Universiti Kebangsaan Malaysia
(External Examiner)
-------------------------------------------------
HASANAH MOHD GHAZALI, PhD
Professor/Deputy Dean
School of Graduate Studies
Universiti Putra Malaysia
Date:
viii

This thesis submitted to the Senate of Universiti Putra Malaysia and has been
accepted as fulfillment of the requirement for the degree of Master of Science.
The members of the Supervisory Committee are as follows:
Annie Christianus, PhD
Lecturer
Faculty of Agriculture
Universiti Putra Malaysia
(Chairman)
Siti Shapor Siraj, PhD
Associate Professor
Faculty of Science
Universiti Putra Malaysia
(Member)
Siti Khalijah Daud, PhD
Associate Professor
Faculty of Science
Universiti Putra Malaysia
(Member)
-------------------------------------
AINI IDERIS, PhD
Professor/Dean
School of Graduate Studies
Universiti Putra Malaysia
Date: 8 March 2007
ix

DECLARATION
I hereby declare that the thesis is based on my original work except for
quotations and citations which have been duly acknowledged. I also declare that
it has not been previously or concurrently submitted for any other degree at UPM
or other institutions.
--------------------------------------
MOHD ZAFRI BIN HASSAN
Date: 15 February 2007
x

TABLE OF CONTENTS
DEDICATION
ABSTRACT
ABSTRAK
ACKNOWLEDGEMENTS
APPROVAL
DECLARATION
LIST OF TABLES
LIST OF FIGURES
LIST OF ABBREVEATIONS
Page
ii
iii
v
vii
viii
x
xiii
xv
xix
1. INTRODUCTION
1.1 Background of Patin buah in Malaysia
1.2 Statement of problems
1.3 Significance of the study
1.4 Objectives
1
2
3
4
2. LITERATURE REVIEWS
2.1 Taxonomy
2.2 Distribution of the family Pangasiidae
2.3 Catfishes as an Economic commodity
2.4 Morphological characters of the genus Pangasius nasutus
2.5 The biology of catfishes
2.6 Reproductive dynamics
2.6.1 Spawning pattern and cycle of ovarian development in
catfishes
2.6.2 Testicular development of catfishes
2.7 Histology of the gonadal development
6
9
11
12
14
15
17
19
20
3. MORPHOLOGICAL VARIATIONS BETWEEN Pangasius nasutus
AND Pangasius conchophilus
3.1 Introduction
3.2 Materials and methods
3.2.1 Study area
3.2.2 Samples collection
3.2.3 Sampling methods
3.2.4 Morphometric and meristic characters
3.2.5 Statistical analysis
24
25
25
26
27
31
35
xi

3.3 Results
3.3.1 Morphological features for characterizing P. nasutus and
P. conchophilus
3.3.2 Meristic characters
3.3.3 Morphometric characters
3.4 Discussion
36
36
39
40
51
4. GAMETOGENESIS IN Pangasius nasutus
4.1 Introduction
4.2 Materials and methods
4.2.1 Field sampling
4.2.2 Gonads collection and macroscopic observations
4.2.3 Histological preparation for gonad studies
4.2.4 Oocyte and spermatogenic stages
4.2.5 Fecundity estimation
4.2.6 Statistical analysis
4.3 Results
4.3.1 Samples landed and standard length-weight relationship
4.3.2 Water parameters, rainfall and water level of Pahang
River near Maran
4.3.3 Biological indices
4.3.4 Macroscopic observation of the ovaries of P. nasutus
4.3.5 Macroscopic observation of the testes of P. nasutus
4.3.6 Microscopic observations on the individual stage of
oocytes in P. nasutus
4.3.7 Microscopic observations of the whole-section of
ovarian development of P. nasutus
4.3.8 Microscopic observations on the spermatogenic cells of
P. nasutus
4.3.9 Microscopic observations of the whole-section of
testicular development of P. nasutus
4.3.10 Seasonal development in the gonadal stages of P.
nasutus
4.3.11 Homogeneity of the ovary and fecundity of P. nasutus
4.4 Discussion
55
56
56
56
58
63
64
65
66
66
68
72
75
77
76
87
90
92
94
96
99
5. GENERAL DISCUSSION AND CONCLUSION
5.1 General discussion
5.2 Conclusion
REFERENCES
APPENDICES
BIODATA OF AUTHOR
108
118
120
133
139
xii

LIST OF TABLES
Table
Page
1 Subgeneric classification of genus Pangasius 8
2 The presence of genus Pangasius recorded in Malaysia 9
3 Morphometric data taken were all according to Pouyaud
et. al. (1999). With exception for measurements with *
were after Gustiano et. al. (2004), after Lowe-McConnell
(1975) and *** additional measurements in the present
study
4 Number of specimens with their respective meristic
counts
32
39
5 Morphometric data of P. nasutus (n = 20) 41
6 Morphometric data of P. conchophilus caught from
Maran (n = 20)
7 Morphometric data of P. conchophilus caught from
Pekan (n = 20)
8 Variables that were significantly different (P < 0.05) in
percentage of standard length (in % SL) (n = 20).
9 Variables that were significantly different (P < 0.05) in
percentage of predorsal length (in % PDL) (n = 20).
10 Variables that were significantly different (P < 0.05) in
percentage of head length (in % HL) (n = 20).
11 Standardized canonical discriminant function coefficients
for ratio percentages
12 Structure matrix of canonical discriminant function
coefficients for ratio percentages
42
43
44
45
46
48
49
13 Classification results based on ratio percentages 50
14 Stepwise dehydration with a series of alcohol and
subsequent paraffin wax infiltration
59
xiii

15 Step-by-step staining procedure 61
16 Mean±SD biological indices of P. nasutus females
caught from the Pahang River near Maran from October
2004 to September 2005
17 Mean±SD biological indices of P. nasutus males caught
from Pahang River off Maran from October 2004 to
September 2005
72
73
18 Size range of oocyte stages of P. nasutus 78
19 Estimated fecundity and frequency of spawning of P.
nasutus collected from the Pahang River near Maran
during the sampling period from October 2004 to
September 2005
98
xiv

LIST OF FIGURES
Figure
1 Taxonomic hierarchy leading to the Family Pangasiidae
(Source: Systema Naturae, 2000)
Page
7
2 Map of study area 25
3 Lateral view of the body; a) P. nasutus, b) P.
conchophilus caught in Maran
4 Methods used for samples collection; a) drift-net; b) longlines;
c) fishing rod; and d) cage containment in the
vicinity of study area
5 Diagram of fishing gears used, a) drifting gillnet; b) longlines
6 Diagrammatic representative of measurements taken on
specimens (adapted from Pouyaud et. al. (1999) with
modifications)
27
29
30
34
7 Counts of gill raker of the first gill arch 35
8 Lateral view of the head; a) P. nasutus, b) P.
conchophilus
9 Side by side comparison of dorsal view of the head; a) P.
nasutus, b) P. conchophilus
10 Ventral view of the head; a) P. nasutus, b) P.
conchophilus
11 Gutted belly showing swim bladder position located at
the abdominal cavity of the body in P. nasutus; a) male,
b) female
12 Canonical discriminant functions plots using proportional
values
37
37
38
38
50
13 Diagrammatic procedures of tissue histology process 62
14 Length-size class of total specimens caught throughout
the study period
66
xv

15 Log 10 -transformed length-weight relationship of P.
nasutus caught from Pahang River near Maran
16 Water surface temperature, dissolved oxygen (D.O) and
specific conductivity (SpC) taken from the Pahang River
near Maran during the sampling period from October
2004 to September 2005. Mean±SD are subject to Tukey
HSD in which dissimilar letters are significantly different
(P

24 Nucleolar stage. Chromatin nucleolar stage; a) nucleoli in
the nucleus present as chromatin form and more
numbers of nucleoli are visible (100x); b) nucleoli are
moving toward the nucleus periphery. Follicular layer
appear as purple stained layer surrounding the oocyte
(40x). Perinucleolar stage; a) Nucleoli allocated
peripherally to the nucleus. Cytoplasm is stained light
blue (20x); b) Dark spot granules can be observed
alongside the follicular layer. A sign of the formation of
granulosa layer (40x)
25 Cortical alveoli stage, a) Early cortical alveoli stage with
translucent dots at the peripheral oocyte indicating the
presence of yolk vesicles (40x); b) Follicular envelope
showing the developing vitelline membrane (100x); c)
More ‘round’ yolk vesicles are surrounding the ooplasm
periphery (20x); d) The prominent yolk vesicles are a
result of the coalescence of the prior yolk vesicles (100x)
26 Early vitellogenic stage; a) Formation of yolk globules
forming an eosin-stained ring around the nucleus (20x);
b) Yolk vesicles still remained at the peripheral ooplasm
(100x)
27 Vitellogenesis stage; a) Yolk globules filling up the
ooplasm (5x); b) Peripheral ooplasm is filled up with
smaller yolk globules, striated vitelline envelope is
evident (100x)
28 Late vitellogenesis stage; a) oil droplets present in the
ooplasm and the start of germinal vesicle breakdown
(10x); b) germinal vesicle leaves the nucleus and moves
towards the animal pole at the peripheral ooplasm and
yolk begins to coalesce (10x)
29 Atretic oocytes; a-b) atresia during cortical alveoli (20x);
c-d) atresia during vitellogenesis (40x); e-f) final stage of
atresia (100x and 20x, respectively)
30 Resting ovarian stage (from a sample of 1600g BW,
43cm SL and 0.25 GSI)
31 Ovarian development at GSI ≤ 1.0; a) Progressing -
maturing (from a sample of 910g BW, 45cm SL and 0.14
GSI); b) Regressing - spent (from a sample of 710g BW,
43cm SL and 0.44 GSI).
81
82
83
84
85
86
87
88
xvii

32 Ovarian development at GSI 1.1 – 5.0; a) Progressing -
mature (from a sample of 1050g BW, 41cm SL and 2.02
GSI); b) Regressing - running (from a sample of 700g
BW, 36cm SL and 2.38 GSI).
33 Ovarian development at GSI ≥ 5.1. Spawning (from a
sample of 1300g BW, 45cm SL and 7.95 GSI).
34 Developmental stages of spermatogenic cells; a)
spermatogonia; b) spermatocytes; c) spermatids;
appearance is blotchy and in clutch form; spermatozoa;
mature spermatozoa have distinct basophilic spherical
heads
35 Testicular development of P. nasutus; a) Early
spermatogenic stage; (from a sample of 45cm SL, 930g
BW and 0.14 GSI); b) Spermatogenic stage; (from a
sample of 54cm SL, 1450g BW and 0.85 GSI); c)
Maturation stage; (from a sample of 41cm SL, 780g BW
and 3.35 GSI); d) Spent stage; (from a sample of 44cm
SL, 770g BW and 1.06 GSI).
36 Frequency of occurrences of ovarian development of the
females and males of P. nasutus caught from the
Pahang River near Maran from October 2004 to
September 2005. Number in parenthesis ( ) represents
the number of specimens caught
37 Frequency of occurrences of ovarian development of the
females and males of P. nasutus caught from the
Pahang River near Maran from October 2004 to
September 2005. Number in parenthesis ( ) represents
the number of specimens caught
89
90
91
93
95
96
xviii

LIST OF ABBREVIATIONS
Analysis of Variance
Body weight
ANOVA
BW
Celsius degree °C
Centimeter
Department
Fatsomatic index
Gonadosomatic index
Gut repletion index
Gram
Head length
Hepatosomatic index
Kilogram
Meter
Milimeter
cm
Dept.
FSI
GSI
GRI
g
HL
HSI
kg
m
mm
Micrometer µm
Percent %
Predorsal length
Standard deviation
Standard length
Universiti Putra Malaysia
PDL
SD
SL
UPM
xix

CHAPTER ONE
INTRODUCTION
1.1 Background of Patin buah in Malaysia
Patin buah, a vernacular river catfish name for Pangasius nasutus in Malaysia, is
one of the favourite food fish and commands a good price in the local market.
Information on this native fish is lacking probably attributed to the dominant
interest in the other patin, Pangasius hypopthalmus, a catfish of Thai origin
introduced to Malaysia for aquaculture purpose. Popularity of the native patin
buah then had been brought up by the recent awareness of its economic value
and the declining of its population in the Pahang River.
The occurrence and distribution of P. nasutus in Malaysia are literally not
conclusive. Catfishes are known to occupy habitats ranging from upland streams
to large river channels and to seasonal floodplain lagoons (Winemiller and Kelso-
Winemiller, 1996). Therefore it is not a surprise that P. nasutus was known to
occur in the Pahang River where the richness of the biodiversity is at its best
among the rivers in Malaysia (Haslawati et al., 2004). Roberts and Vidhthayanon
(1991) also reported the occurrence of this species in Chenderoh Dam, Perak.

A number of species of the family Pangasiidae are of great economical
importance in Southeast Asia (Hung et al., 2004) and have high potential for
aquaculture in Malaysia. At present, the wild catch of patin buah (Pangasius
nasutus) and patin muncung (Helicophagus wandersii) demands as much as RM
50kg -1 and RM 100kg -1 in the market, respectively. Due to its white and tender
flesh, Pangasiid catfish was ranked among the top five preferred species for five
consecutive years in terms of consumer preferences in Malaysia (Fisheries
Annual Report, 2002).
1.2 Statement of problems
Recently, the decline in the abundance of patin buah in the local rivers has been
reported. In fact, it is supported by the declining numbers in landing data of the
species in Maran, a district along the Pahang River, which is known for patin
buah (Department of Fisheries, 2004). The first successful artificial propagation
however, was reported by the local Department of Fisheries in March 2004 after
several years of attempt at propagating it. Despite the success, however
continuous fry supply however cannot be guaranteed due to low survival rate of
repeated attempt.
P. conchophilus that is found in the vicinity of Pahang River was recently brought
in from Thailand by the Cambodian immigrants residing in Pekan, Pahang
(Haslawati et al., 2004). Due to its resemblance to P. nasutus, it was named by
2

the local people as ‘patin buah Kemboja’ (Cambodian patin buah). These two
species are commonly mistakenly misidentified for each other due to
morphological features of both species (Roberts and Vidthayanon, 1991).
Although induced breeding has been successful, studies on the reproductive
biology of the species sampled from its natural environment are crucial so as to
gain insight and more understanding on the species. Even for fish that has been
established in a farming system, the information on the reproductive aspects
including the absolute and relative fecundities would be helpful to ensure a
continuing success in its culture (Ali, 1993). These guidelines also constitute
major approach towards establishing biodiversity management as well as
breeding programme (Corriero et al., 2003; Utoh et al., 2003; Micale et al., 1996;
Legendre, 1986).
1.3 Significance of the study
The population of P. nasutus is currently declining. In the present situation, the
marketable supply patin buah is entirely dependant on the wild catch. This
increases the chances for the fish to be over-exploited. Effort at culturing this
species has never been attempted and the population silently decreasing.
Therefore, a study on the gonadal cycle of the species is necessary as an initial
step towards husbandry management.
3

Reproductive biology has served numerous advantages in the study of a
particular species or population. Manosroi et al. (2003) stated that in order to
conserve a threatened Mekong giant catfish P. gigas, maturation induction by
hormone injection and seasonal endocrine regulation expressed as
gonadosomatic index (GSI) are crucial. Knowledge in the reproductive biology
can also lead to a better understanding and advantage in breeding a particular
species before being introduced for aquaculture purposes (Hassin et al., 1997).
Temporal difference in reproductive maturity at individual level allows an efficient
broodstock management (Dahle et al., 2003).
The study on annual cycles in the gonadal stages of wild animals will provide
baseline information on body composition, which is useful in the evaluation of
quality and physiological condition of animals before being cultured (Craig et al.,
2000). Conservation, catch size restrictions, controlled fishing seasons or
improvements of breeding technologies in hatcheries can be inferred from the
study.
1.4 Objectives
The main objective of this study is to describe the distinctive morphological
characteristics of the native P. nasutus and to differentiate these characteristics
from those of the introduced P. conchophilus. Apart from that, monthly
observation and assessment on the gonadal activity of P. nasutus caught from its
4