MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF Pangasius...

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


MASTER OF SCIENCE

UNIVERSITI PUTRA MALAYSIA

2006


By


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


By


June 2006

Chairman : Annie Christianus, PhD 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

Oleh


Jun 2006

Pengerusi : Annie Christianus, PhD 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 berperingkat-

peringkat pada sesuatu tempoh masa. Keadaan ini menunjukkan bahawa P.

nasutus merupakan pembiak yang melepaskan telurnya secara berperingkat-

peringkat 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

Page DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL DECLARATION LIST OF TABLES LIST OF FIGURES LIST OF ABBREVEATIONS

1. INTRODUCTION 1.1 Background of Patin buah in Malaysia 1.2 Statement of problems 1.3 Significance of the study 1.4 Objectives

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

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

ii iii v vii viii x

xiii xv xix

1 2 3 4

6 9 11 12 14 15 17

19 20

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

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 5. GENERAL DISCUSSION AND CONCLUSION

5.1 General discussion 5.2 Conclusion

REFERENCES APPENDICES BIODATA OF AUTHOR

36 36

39 40 51

55 56 56 56 58 63 64 65 66 66 68

72 75 77 76

87

90

92

94

96 99

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

32

4 Number of specimens with their respective meristic

counts 39

5 Morphometric data of P. nasutus (n = 20) 41

6 Morphometric data of P. conchophilus caught from Maran (n = 20)

42

7 Morphometric data of P. conchophilus caught from

Pekan (n = 20) 43

8 Variables that were significantly different (P < 0.05) in

percentage of standard length (in % SL) (n = 20). 44


percentage of predorsal length (in % PDL) (n = 20). 45


percentage of head length (in % HL) (n = 20). 46

11 Standardized canonical discriminant function coefficients

for ratio percentages 48

12 Structure matrix of canonical discriminant function

coefficients for ratio percentages 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

72

17 Mean±SD biological indices of P. nasutus males caught

from Pahang River off Maran from October 2004 to September 2005

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 Page

1 Taxonomic hierarchy leading to the Family Pangasiidae (Source: Systema Naturae, 2000)

7

2 Map of study area 25

3 Lateral view of the body; a) P. nasutus, b) P. conchophilus caught in Maran

27

4 Methods used for samples collection; a) drift-net; b) long-

lines; c) fishing rod; and d) cage containment in the vicinity of study area

29

5 Diagram of fishing gears used, a) drifting gillnet; b) long-

lines 30

6 Diagrammatic representative of measurements taken on

specimens (adapted from Pouyaud et. al. (1999) with modifications)

34

7 Counts of gill raker of the first gill arch 35

8 Lateral view of the head; a) P. nasutus, b) P. conchophilus

37

9 Side by side comparison of dorsal view of the head; a) P.

nasutus, b) P. conchophilus 37

10 Ventral view of the head; a) P. nasutus, b) P.

conchophilus 38

11 Gutted belly showing swim bladder position located at

the abdominal cavity of the body in P. nasutus; a) male, b) female

38

12 Canonical discriminant functions plots using proportional

values 50

13 Diagrammatic procedures of tissue histology process 62

14 Length-size class of total specimens caught throughout the study period

66

xv

15 Log10-transformed length-weight relationship of P.

nasutus caught from Pahang River near Maran 67

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<0.05)

69

17 Turbidity, pH and total dissolved solids (TDS) taken from

the Pahang River near Maran during the sampling period from October 2004 to September 2005. Mean±SD shown subject to Tukey HSD in which dissimilar letters are significantly different (P<0.05)

70

18 Rainfall (mm) and water level (m) data collected at

Maran Meteorological Station from October 2004 to September 2005

71

19 Biological indices of the females of P. nasutus caught

from the Pahang River near Maran during the sampling period from October 2004 to September 2005

74

20 Biological indices of the males of P. nasutus caught from

the Pahang River near Maran during the sampling period from October 2004 to September 2005

74

21 The macroscopic morphology the ovaries; a) 2.02 GSI

from 1050 g BW and 41 cm SL; b) 8.24 GSI from 800 g BW and 46 cm SL; c) 2.37 GSI from 700 g BW and 36 cm SL ; d) 0.30 GSI from 780 g BW and 45 cm SL; e) 0.25 GSI from 1600 g BW and 49.2 cm SL

76

22 The macroscopic morphology of the testes; a) 1.31 GSI

from a sample of 37 cm in SL and 660 g in BW; b) 6.11 GSI from a sample of 46 cm in SL and 900 g in BW

77

23 Stages of oogonia stage; a) the presence of oogonia

within the ovarian wall (10x); b) closer view of oogonia (100x). Primary follicles stage; a) overall view of the ovarian cavity (10x), primary follicles are in dark colour; b) primary follicles encapsulated in the nest and nucleus is formed with the presence of a single nucleoli (100x)

79

xvi

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)

81

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)

82

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)

83

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)

84

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)

85

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)

86

30 Resting ovarian stage (from a sample of 1600g BW,

43cm SL and 0.25 GSI) 87

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).

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).

89

33 Ovarian development at GSI ≥ 5.1. Spawning (from a

sample of 1300g BW, 45cm SL and 7.95 GSI). 90

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

91

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).

93

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

95

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

96

xviii

LIST OF ABBREVIATIONS

Analysis of Variance ANOVA

Body weight BW

Celsius degree °C

Centimeter cm

Department Dept.

Fatsomatic index FSI

Gonadosomatic index GSI

Gut repletion index GRI

Gram g

Head length HL

Hepatosomatic index HSI

Kilogram kg

Meter m

Milimeter mm

Micrometer µm

Percent %

Predorsal length PDL

Standard deviation SD

Standard length SL

Universiti Putra Malaysia 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.

2

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

3

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.

4

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

MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF Pangasius...

Documents

Transcript of MORPHOLOGY AND GENERAL REPRODUCTIVE STAGES OF Pangasius...