ALONG THE KERALA COAST

276 Pages·2014·6.53 MB·English

by  Anil M K

STUDIES ON THE FISHERY AND CULTURE PROSPECTS
OF MUD CRABS (GENUS SCYLLA de HAAN)
ALONG THE KERALA COAST
THESIS SUBMITTED
IN PARTIAL F ULFILMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
OF THE
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY
BY
M.K. ANIL, M.Sc.
tmfvsn
ICAR
CENTRAL MARINE FISHERIES RESEARCH INSTITUTE
KOCHL68201-4
MARCH 1997
-dedicated to my mother
CERTIFICATE
This is to certify that the thesis entitled ‘Studies on the fishery
and culture prospects of mud crabs (Genus Scylla de Haan) along the
Kerala coast’ is a bonafide original research work conducted by Shri
Anil, M.K., under my guidance and supervision. I further certify that
no part of this thesis has previously formed the basis for the award of
any degree, diploma, associateship, fellowship or other similar titles of
recognition.
Dr. C. Suseelan, M.Sc., Ph.D.
Senior Scientist 8: Officer-in-Charge,
Post Graduate Programme in
Kochl-_14 Mariculture,Central Marine
March 1997_ Fisheries Research Institute,
Kochi-682 O14,
DECLARATION
I hereby declare that this thesis entitled 'Studies on the fishery
and culture prospects of mud crabs (Genus Scylla de Haan) along the
Kerala coast‘ is a record of original and bonafide research carried out
by me under the supervision and guidance of Dr. C. Suseelan, Senior
Scientist, Central Marine Fisheries Research Institute, Kochi and that
no part thereof has been presented for the award of any other degree,
diploma, associateship, fellowship or other similar recognition.
gig.
KOChi_14, M.K. ANIL
March, 1997.
Contents
Preface
Acknowledgements iv
Chapter I Introduction
Chapter II Material and Methods 13
Chapter III : Results and Discussion 31
Section 1. Taxonomy and Distribution 32
Description of species 36
Electrophorefic results 39
Distribution 40
Discussion 41
Section 2. Bionomics and Life History 49
Reproduction 49
Incubation and larval development 61
Growth
Carapace width-weight relationship 78
Behavioural observations
Discussion 30
Section 3. Capture Fishery 95
Fishing methods and seasons 96
Landings 98
Population characteristics 106
Discussion 123
Section 4. Mud Crab Culture 129
Global status 129
Experimental culture 136
Larval feeding and experimental seed production 150
Discussion 156
Chapter IV : Summary 168­
References 175
PREFACE
The mud crabs of genus Scylla have come into prominence in India since
early eighties with the commencement of live crab export to South East Asian
countries. Prior to this new development, the mud crabs formed only a fishery of
sustenance level in isolated brackishwater regions and inshore areas for domestic
marketing. The recent collapse of shrimp aquaculture industry in the country cre­
ated a feeling of uncertainty about the future of coastal aquaculture in India and
in this context the success of mud crab culture in countries like Taiwan, Malaysia,
Philippines and Thailand kindled hope for diversification of the aquaculture in­
dustry in this direction. Realizing the vast potential for development of mud crab
fishery in the Bay of Bengal region, Thailand hosted an international seminar at
Surat Thani to review the status of exploitation, culture and trade of mud crabs in
the member countries of the Bay of Bengal Programme in 1991 and the proceed­
ings of the seminar brought out in 1992 (Anon., 1992b). This seminar revealed that
India lags far behind many of the South East Asian countries in culture and propa­
gation of mud crabs, although the country has vast brackishwater areas ideally
suited for this purpose. The sudden impetus for exploitation of mud crabs in the
brackishwater areas of the country to support the lucrative live crab exportrade is
causing great concern for the sustainability of the wild stocks. This necessitates
appropriate steps for scientific management and conservation of the resource. Mud
crab culture has also not taken root in the country to flourish as an organised
industry in the absence of viable seed production and farming technologies.
Kerala has been one of the leading maritime states in India for the exploita­
tion and export of mud crabs (Raj, 1992). Many brackishwater systems like the
Ashtamudi lake, Vembanad lake, Cochin backwaters and Korapuzha estuary are
well known for their rich population of mud crabs. Realizing the imperative
need to build up a strong scientific base for proper management and conservation
of the resource and also to develop proper technologiesfor seed production and
farming of mud crabs, a detailed study was undertaken on the mud crabs of Kerala
coast and the results are described in the thesis.
The thesis is presented in four chapters. Chapter I deals with a general
introduction which outlines the objectives of the study providing an exhaustive
review of works on crabs with particular reference to mud crabs. Chapter II de­
scribes the material and methods used for the study.
Chapter III include the results and discussion which are presented in four
sections. In the first section, Taxonomy and distribution of mud crabs are dealt
with. Two species of mud crabs encountered during the study are described and
their identity is established on the basis of morphological and electrophoretic stud­
ies. The second section comprises the bionomics and life history in which various
aspects such as reproduction, larval development, growth and behavioral features
are described. The reproductive biology of both the species is described and com­
pared in varying details encompassing the gross structure and histology of repro­
ductive systems, spermatogenesis, oogenesis, ovarian maturation, minimum size
of mature female, fecundity and breeding. Various changes that take place dur­
ing the incubation period as well as during larval development of both the spe­
cies have been elucidated. The growth of the two species has been studied by
rearing crabs in the laboratory and ponds, and also by statistical analysis of size
frequency data of crabs from the capture fishery.
Section three deals with the capture fishery in which fishing methods, sea­
sons, landings and population characteristics such as size distribution, sex ratios
and breeding population in respect of both the species have been dealt with in
detail and discussed.
In the fourth section, briefly describing the mud crab culture techniques,
regional status of mud crab farming in the Indo-Pacific is reviewed, and the re­
ii
‘ sults of fattening and grow out experiments conducted during the study are de­
scribed. Details such as biochemical changes during fattening are also elucidated.
In addition to this, the section deals with the results of larval feeding and experi­
mental seed production of S. oceanica .
Chapter IV gives a summary of the important findings of the study, which
is followed by a detailed list of references on the subject matter.
ACKNOWLEDGEMENTS
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M.K. ANIL