Studies on the Reproductive Physiology and Breeding Biology of the Cultivable Species of Grouper Epinephelus Tauvina (Forsska
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STUDIES ON THE REPRODUCTIVE PHYSIOLOGY AND BREEDING BIOLOGY OF CULTIVABLE SPECIES OF GROUPER EPINEPHEL US T A U VINA (FORSSKAL) THESIS SUBMITTED IN PARTIAL FULFILMENT OF TI-IE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY OF THE COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY /S’ Ii YT/‘Q1 / 1,)‘\_ "V-‘ BY _ ‘ n V ~ vv ':‘J'4 ,__: _ .3 F " , ll ,.\.' I U» . GRACY MATHEW ‘_. 1/J I fl School of Industrial Fisheries COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY COCHIN — 682016 INDIA MARCH 2008 T “\. Mb <’ CERTIFICATE This is to certify that the thesis entitled “Studies on the reproductive physiology and breeding biology of the cultivable species of grouper Epinephelus tauvina (Forsskal)” is an authentic record of research work carried out by Mrs.Gracy Mathew under my guidance and supervision in partial fulfillment for degree of Doctor of Philosophy of Cochin University of Science & Technology under the faculty of Marine Sciences. K 1) .~Ku'ruvilla Mathew MarchCochin-682016 2008 PROFESSOR SUPERVISING (Retd.), GUIDE DECLARATION I, hereby declare that this thesis entitled “Studies on the reproductive physiology and breeding biology of the cultivable species of grouper Epinephelus tauvina (Forsskal)” has not previously formed the basis for the award of any degree, associate- ship, fellowship or any other similar title or recognition. / v , March 2008 Gracy Mathew Cochin-682018 PREFACE According to the projections given by the FAO, in order to maintain the average per capita supply of l7.2kg, it will be necessary to produce nearly 70 million metric tonnes of food fish by 2020, from both capture fisheries and culture fisheries together. This clearly points out that the burden has to be borne by aquaculture as the marine fish production from capture has reached a plateau limit of around 2.7 million metric tonnes in the last decade. India with its enormous potential for sea farming, should harness this to the maximum for increasing the fish production. The marine and brackish water fishes make up an important component in terms of production and value. The development of large and affluent markets for live reef fish in Hong Kong and Southem China has increased pressure on wild stock resources and has led to indiscriminate fishing including destructive fishing methods such as dynamite and cyanide fishing, resulting in the depletion of the natural stocks to an alarming level. Aquaculture of high-value finfish species, such as groupers, is an industry of increasing importance throughout the Asia-Pacific region. The estuarine grouper Epinephelus tauvina is one of the species used foremost in mariculture for the last two decades in the Southeast Asian countries, because of its high market demand, fairly fast growth rate, good food conversion ratio, disease resistance and tolerance to crowding. The growing demand for quality seed coupled with uncertainty of availability from nature at the appropriate time in required quantities has prompted research on problems connected with seed production. Attempts on breeding and hatchery production of seeds of groupers are progressing actively in many countries world around. But a number of lacunae still remain for optimizing ii commercial seed production. The significance of developing a technology for brood stock development and breeding in captive condition is imperative in ensuring seed availability at the required time. To develop a genetic programme to improve the population characteristics, it is necessary to control maturation and reproduction in captivity. In order to proceed with controlled reproduction or artificial means of reproduction to produce good quality eggs, an in-depth knowledge of the reproductive biology, various stages of gonad maturation, physiology of spawning etc. should be known. The present study envisages the objectives of obtaining a detailed picture of the physiology of reproduction ie. ,*th'e oogenesis and spermatogenesis in the protogynous estuarine grouper E. tauvina. The results of the entire studies are embodied in the present thesis. It starts with a general introduction, covering the present status of our knowledge on the subject and emphasizes the importance of the subject of investigation. Subsequent to this, there are five separate chapters, covering different aspects such as the female reproductive system and the process of oogenesis, hermaphroditism, sex-inversion, male reproductive system and spermatogenesis, breeding biology including brood stock development, fecundity, spawning, incubation and hatching etc. The sixth chapter is on grouper culture, and there is also a chapter that pertains to the taxonomical aspects and distribution of commercially important species of groupers, including E. tauvina. Each chapter begins with an introduction, followed by materials and methods, results and discussion. Introductory part of each chapter highlights the importance of the particular aspect of study and also reviews literature pertaining to it. Materials and methods explain the materials and techniques used as well as the procedures adopted for data analysis. The data obtained are presented in the results jwith necessary iii figures and tables. Each chapter is concluded with a discussion about the salient findings of the study. Chapter two deals with the phylogenic taxonomy of groupers as well as taxonomic status and distribution of six commercially important species. This study was carried out because phylogenetic systematics among the groupers are poorly known and relationships among the genera have been the subject of much disagreement. The salient diagnostic characters of each species along with the geographical distribution are given. Control of reproduction of the candidate species is one of the most important aspects of aquaculture management; for ensuring high quality seed production and genetic improvement of stock. For carrying out artificial means of reproduction aquaculturists must be fully aware of the gonadal maturation stages, spawning seasons and status of the brooders during spawning. The third chapter on the female reproductive system and development of the ova explains the general anatomy of the various stages of the ovary; the methods of determining the reproductive cycle and the developmental changes in the gonads through microscopic observations. In E. tauvina, in fishes measuring 38-40cm in total length, the females can be distinguished by the presence of pinkish, translucent, ribbon-like strands of gonadal tissue. Ovarian maturation was classified into six developmental stages mainly based on the changes in size, shape, colour, diameter of oocyte and on microscopic structure of the ova. The production of egg, well equipped with the necessary reserve food for the developing embryo, occurs through the processes taking place in the germ mother cells of the ovary. Clear knowledge of the precise stage of gonadal maturation is highly essential for the iv selection of female spawners for breeding and seed production. This process of oogenesis has been studied by the use of histological methods. In the present study, for captive spawning of E. tauvina which is a protogynous hermaphrodite, male brooders were developed by transforming female fish to male. Sex reversal was effected by oral administration of l7o<: methyl testosterone (MT) through trash fish used as feed . Chapter four deals with sex inversion through hormone application, description of male reproductive organ and spermatogenesis using histological and cytological criteria . The progressive development of male tissues and transformation to the male gonad is sequentially followed with increase in the dosage of the male hormone. Spermatogenesis was found to involve progressive reduction in \ cytoplasmic volume and condensation of chromatin matter. In the next chapter breeding biology of the estuarine grouper E.tauvina is dealt in detail. Natural spawning of the species by environmental manipulation under captive condition is given. Effect of lunar periodicity on the natural breeding of grouper is also elucidated. Fertilization rate, incubation and hatching rate of the buoyant, viable eggs are dealt with in this chapter. The Sixth chapter is on the farming or culture of groupers. The global scenario and the current methods of grouper farming world over are summarized here. Experimental culture of groupers carried out in the onshore recirculating system using different stocking densities are also elucidated. The last chapter is a summary of conclusions, which constitute the overall findings of the study carried out and conclusions drawn from it. Literature cited in the entire study is listed under the reference given at the end of the thesis. Acxowczmgmmw I wisli to express my deep sense of gratitude and irulefitedness to Q’rof (0)11) Kuruvilflz Matfiew, @ro]‘essor (Retd), S cfiool of Industrial Tisfieries, (Department Qf 9|/tarine Sciences, Cocfiin University qf Science and ‘Ieclinolbgy, for t/ie guidance, invalualile suggestions and constant encouragement for tfie successful completion oftlie work, My tlianfls are due to G)r. 9i/l._7.:Mod'ayil,, (Dr. Wt. (Devaraj and (Dr. ‘VJN Gfilfiz, former (Directors of tlie Central Marine Tzlslieries Qiesearcfi Institute, Cocliin, for giving me tlie opportunity to carry out tliis study using tlie eagcelfint mariculture facilities at tlie Lafioratory at tlie Tislieries iflarliour; ‘Ifioppumpady. I am liiglily indefited to all my colleagues at tfie erstwliile <Fislieries 7{ar6our Lalioratory of C9WI-‘RI, for tlieir wliole liearted support during tlie course of my work; I wilsli to tlianfi