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Percoidei, Sillaginidae) STUDIES ON THE REPRODUCTION OF INDIAN WHITING Sill/160 5'/HAM/1 (FORSKAL) (PERCOIDEI, SILLAGINIDAE) THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY OF THE COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY By P. JAYASANKAR, M. Sc. CENTRE or-" ADVANCED STUDIES IN MARICULTURE cocHIN-682031CENTRAL. MARINE FISHERIES RESEARCH INSTITUTE ' JUNE ‘I989 CERTIFICATE This is to certify that the thesis entitled "STUDIES ON THE REPRODUCTION OF INDIAN WHITING SILLAGO SIHAMA (FORSKAL) (PERCOIDEI, SILLAGINIDAE)" is the bonafide record of the work carried out by Shri. P. Jayasankar under my guidance and supervision and that no part thereof has been presented for the award of any other degree. Dr. K. Alagarswami, Director, Central Institute of Brackish water Aquaculture, I2, Leith castle street, Santhome, Madras - 600 028. DECLARATION I hereby declare that this thesis entitled "STUDIES ON THE REPRODUCTION OF INDIAN WHITING SILL/-1G0 SIHAMA (FORSKAL) (PERCOIDEI, SILLAGINIDAE)" has not previously formed the basis for the award of any degree, diploma, associateship, fellowship or other similar titles or recognition. CochinJune, 1989 — 682 031 P. JAYASANKAR CONTENTS PAGE PREFACE ACKNOWLEDGEMENT CHAPTER I INTRODUCTION I0 CHAPTER II MATERIALS AND METHODS II 24 CHAPTER III TAXONOMIC CONSIDERATIONS OF THE 25 39 SILLAGINID FISHES FROM PALK BAY AND GULF OF MANNAR CHAPTER IV MATURATION AND SPAWNING 40 75 CHAPTER V HISTOLOGY OF GONADAL DEVELOPMENT 76 II7 CHAPTER VI BIOCHEMICAL CHANGES DURING II8 I47 MATURATION AND SPAWNING CHAPTER VII HISTOCHEMISTRY OF OOCYTES DURING I48 I67 MATURATION CHAPTER VIII PRELIMINARY EXPERIMENTS ON THE I68 I78 INDUCED MATURATION AND SPAWNING SUMMARY I79 I81} REFERENCES I85 25I PREFACE From the point of view of rational exploitation and proper management of the fishery resources as well as for the development of intensive aquacult­ ure of fishes through selective breeding, brood stock development, domestication and genetic improvement, a sound knowledge of reproductive biology and physiology of the candidate species is of great importance. In recent times, a wealth of information on maturity, spawning habits, spawning periodicity, spaw­ ning season, size at maturity and fecundity of commercially important fishes has been generated. Gametogenesis involves the transformation of Primordial germ cells in the gonads into specialised cells or gametes, namely ova in the female and sperms in male, through a series of complex morphological and cytological events. The formation of male gamete is known as spermatogenesis. In the female, the primary growth phase involving the formation of primary oocyte from oogonia is known as oogenesis, which would be followed by the secondary growth phase, in which considerable increase in the size of the oocyte occurs, due mainly to accumulation of yolk. This process is known as vitellogenesis, which would be followed by final maturation and ovulation of the ova. In the present work, basic aspects of maturation and spawning, salient features of gametogenesis and associated biochemical changes occurring during these processes in an important cultivable fish, Sillago sihama belonging to the family Sillaginidae have been investigated. The fishes belonging to the family Sillaginidae, commonly known as ‘sand whitings‘ or ‘sand borers‘, are distributed in the shallow estuarine and near coastal waters of Indo-West Pacific region. Few species are also known to ascend the freshwater regimes of the river. The sillagi­ nids contribute to small but commercially important fisheries throughout the range of their distribution (Mckay, I985). The sillaginids are gaining importance in fish farming. At present sillaginid culture is in its beginning stage and restricted to few countries. But they have great potential for augmenting fish production through aquaculture. Characteristics such as capacity to tolerate wide fluctuations in environmental conditions, fast growth rate and above all their great demand as a delicious table fish, make sillaginids favourite candidate species for culture in coastal sea water, estuaries and brackishwaters. In India, the sand whitings are caught all along the coast in nearshore seas, estuaries and brackish water lakes. Some of the important fishing areas in the country are Chilka lake, Kakinada, Vicshakhapatnam, Pulicat lake, Palk Bay, Gulf of Mannar, backwaters of Kerala, Karwar., Netravathy and Gangolly estuaries. Among the different species of Sillaginids occurring in the Indo­ West Pacific region, Sillago sihama is the most widely distributed species. In Indian waters, studies on the seed availability of this species have indicated that large numbers of fry and fingerlings could be collected from the inshore waters, estuaries and backwaters almost throughout the year. This offers immense propsects for large scale culture of the iii species in the country. Preliminary experiments of the culture of S. sihama have been carried out at Mandapam and Mangalore. Some information is available on the biology, breeding, larval rearing and tank culture of Sillaginids. However, the taxonomic status of the family Sillaginidae has been in a confused state and a comprehensive knowledge on maturation, spawning and gametogenesis of $.s.ihama is lacking. In view of these lacunae investigations on different aspects of reproduction in this speci­ es along with a systematic study of the sillaginids from the area of present work were taken up and the results are presented in this thesis. The thesis is presented in 8 chapters. Chapter-I surveys the literat­ ure on distribution, fishery, taxonomy, biology and culture aspects of sand borers of the Indo—West Pacific region. Various methodologies employed in the present study are mentioned in Chapter-II, followed by taxonomic consideration of the whiting species from Palk Bay and Gulf of Mannar. In Chapter-IV, general aspects of reproductive biology, such as external morpho­ logy of gonads, classification of maturity stages, spawning season, gonado­ somatic index, size at maturity, fecundity and sex-ratio are considered. In Chapter—V, histological structure of gonads and the cellular changes occurring during oocyte growth and spermatogenesis are discussed. Chapter-VI deals with the biochemical changes occurring in certain somatic tissues and the gonads with respect to maturation. Results of the histochemical changes taking place in the oocytes during maturation are discussed in Chapter—VII. Finally in Chapter-VIII, results of some preliminary experiments carried out on induced maturation and spawning of the species are presented. iv The study reveals that 6 species of fishes belonging to the family Sillaginidae occur in the Palk Bay and Gulf of Mannar, among which Sillago sihama accounts for about 60 percent of all the species in the commercial landings at Mandapam and surrounding areas. The other species in the order of abundance are Sillago indica, S. argentifasciata, S. soringa, 5. vincenti and S. chondropus. It is found that S. sihama is a prolonged breeder whose spawning season extends from July to February. The size at first maturity of the female is slightly more than that of male. 5. sihama is a high fecund fish, whose fecundity is curvilinearly related to length and linearly related to both body weight and ovary weight. Month­ wise sex—ratio is not significantly different from 1:1 ratio, though females out-number males significantly above I70 mm (total length) in the commercial catches. The ovary is of the cystovarian type and the testis lobular type with unrestricted distribution of spermatogenic cells. In the oocytes, thecal layer is poorly defined and the zona radiata has a bipartite structure. Zona radiata interna shows undulated nature in the secondary and tertiary yolk granule oocytes, which is indicative of the micropinocytotic activity in connection with vitellogenesis. Yolk mass formation is of the 'continuous' type. Lamp-brush chromosomes are detected in the nucleus of Vacuolated oocyte stage which disappear as the maturation of oocytes proceed. Nuclear membrane exhibits 'bleb' formation in the Primary yolk granule oocyte stage. Four stages of atresia are recognized in the vitellogenic follicles. Yolk granule oocytes and hyaline oocytes are relatively more important than the other oocyte stages in the mature and ripe ovaries respectively. During maturation, carbohydrates, protein and lipid from the body get translocated to the gonads for the formation of gametes and hormones. Carbohydrates are detected richly in the zona radiata externa and yolk vesicles of the oocytes. Lipid yolk makes its appearance first, followed by yolk vesicles and protein yolk almost simultaneously. DNA content is detectable only in the nucleus of pre-vitellogenic oocytes. 'Nucleolar extrusions‘ are observed. With carp pituitary gland extract and HCG, the species could be made to spawn in the laboratory; other details of the results are discussed. These are some of the original contributions of the present investigation. The results of the work have cleared the confusion about the taxonomy of whitings from Palk Bay and Gulf of Mannar, contri­ buted new information about the finer aspects of reproduction in Sillago sihama and showed that this species could be induced to spawn in the laboratory, which forms the initial step for the development of its artificial propagation programme for intensive aquaculture. ACKNOWLEDGEMENT This study was carried out under the guidance of Dr. K. Alagarswami, Director, C.I.B.A., I2, Leith castle
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