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Journal of the Marine Biological Association of India Journal of The Marine Biological Association of India ABBREVIATION : J. mar. biol. Ass. India Vol. 35 June and December 1993 No. 1 & 2 THE RATE OF GROWTH OF SPAT AND YEARLINGS OF THE PEARL OYSTER PINCTADA RADIATA (LEACH) OF BAHRAIN WATERS K. NAGAPPAN NAYAR AND MOHAMMED AL-RUMAIDH Bahrain Centre for Studies and Research, P.B. No. 496, Manama, Bahrain ABITRACT Two batches of pearl oyster spat were collected from one of the offshore pearl banks on Ifth November 1987 and 1st December 1987 and their linear msasurements were recorded. They were put in two separate cages and reared suspending the cages at No. 3 Beacon. Periodical measurements were recorded of the spat and their rate of growth was studieci. This preliminary study has indicated that the spat grows to a length of about 45 mm within one year and 70 mm approximately in 2 years. Rate of growth appears to be slightly faster in Bahrain waters, compared to the observations made in India and Japan. Although the data have been analysed mainly on dorso-ventral measure­ ments, the average growth in width, hinge length and thickness have also been given. The tempe­ rature', salinity and pH of the waters of the pearl banks during the period of observation have bem recorded. iNTRODt^CTiON This change made all the pearl divers abandon their age old traditional occupation and taken PEARL fishing has been going on in Bahrain to more lucrative jobs available onshore, which waters from time immemorial and the pearls ultimately led to the natural death of pearl obtained from the oysters of the area were fishing in Bahrain by early sixties. considered to be far superior than those harves­ ted from the nearby pearling countries. Pearl In 1985 the Bahrain Centre for Studies and diving was the profession for a very large Research in its regular research programme number of Bahrainis till the advent of oil. included a feasibility study to find out the A switch over from the profession took place present status of the pearl oyster beds with from then on and most of the divers got more a view to ascertaining the possibility of comfortable shore jobs, with better remunera- reviving the age old traditional pearl fishery tion, due to the establishment of oil companies, of Bahrain. This programme was initiated K. NAGAPPAN NAYAR AND MOHAMMED AL-RUMAIDH by AUou'h (1985) and the preliminai7 and growth of the oysters found in the coast a investigations carried out by him were published waters of Kuwait. Almatar et al. (1983) in the form of a report. Under this programme, have given an account of the pearl oyster research on various aspects of pearl oysters fishery of Kuwait and have also studied the are being pursued and the study on the early size composition of the oysters collected from rate of growth of spat and yearlings of the the market. pearl oyster Pinctada radiata (Leach) is one amongst them. In India, Sri Lanka, Japan and Australia, earlier workers have carried out extensive By scanning the available literature, it is seen studies on various aspects of biology, physio­ that not much of scientific research has been logy, etc. on pearl oysters dating back from carried out on the biology or growth of the the beginning of this century. Herdman (1903) pearl oysters of this region. Bowen (1951)^ carried out elaborate work including biology Belgrave (1960, 1968), Belgrave, J.H.D. (1975)^ of the pearl oysters found in the Sri Lanka Lorimer (1951), and Datta and Nugent (1985) Coast. His work was followed by Hornell are some of the important authors who have (1922), Devanesan and Chidambaram (1956), published very valuable information regarding Gokhale et al. (1954), Narayanan and Michael the detaih of fishery, the exact location of the (1968), Pandya (1975), Alagarswami and different pearl oyster beds, the number of Chellam (1977), Nayar et al. (1978) and Chellam divers engaged in the fishery, etc. (1978). Similar studies have also been made in. Jnpan by Kobayashi (1948) and Kobayash and Tabota (1949) and by Nicholls (1931) in Chidambaram (1958) as given by Devanesan Australia. and Chacko (1958) took a consignment of paarl oysters from Bahrain in 1959 to Tuticorin The authors sincerely thank Dr. Hamed Ali and Krusadai Island in India to repopulate, Sulayti, Secretary General, Bahrain Centre barren pearl oyster beds of that region. In for Studies and Research for giving necessary his report, he has given some general informa­ encouragemei^.t during the course of this study, tion regarding the pearl fishery in the Arabian They are also thankful to Dr. Sami Dannish, Gulf ?nd tbe seg conditioas such as temperature, Director, Scientific Research Department. salinity, etc. of the Bahrain waters. Vousden BCSR for his encouraging discussions during (1985 A) has mentioned that the trade about the progress of this work and offering his 80 years ago was valued at B.D. 500,000 and valuable comments for the improvement of this provided employment for 20,000 men. He has paper. They are thankful to their colleagues also men ioned that in 1915 it was the premier for the help rendered in the preparation of industry of the Gulf, employing 4,500 boats some of the graphs and Tables and also in with over 74,000 men. His report is taking periodical measurements of the spat. rather a review with some suggestions than a feasibility study as no actual work has MATERIAL AND METHODS carried out by him. Vousden (1985 B), along with some other scientists of the Bahrain One sample cf spat and oysterlings numbering Centre for Studies and Research surveyed a 29 from Bl Jaal (26° 38' 89" N - 50° 59' 80" E) few offshore oyster beds for eight days in was collected on 16th November 1987 and the August, 1987. Mohammad (1972, 1976) from length, width, hinge length and thick­ Kuwait has studied the infestatioa of pearl ness of the oysters were measured. The oysters by a new species of Polydora and also sample was grown in a cage with mesh size; workedout the relationship between biofouling of 3 mm and suspended at No. 3 BeacoQ GROWTH RATE OF PINCFADA RADIATA SPAT AND YBARUNGS (26°3' 52' N-5r 33' 00" E). As the sample RESULTS size was too small, one more sample of spat was collected from the same bed on 25th Growth in dorsoventral measurements November 1987 and all the measurements as The sample No. 1, taken on 16th November mentioned above were taken and the oysters 1987 (Fig. 1 Al, Tabic 4) indicates the presence reared at No. 3 Beacon. It so happened of tliree modes at 5-10 mm, 15-20 mm and that on 1st December 1987 the second cage 30-35 rom. This shows that they belong to was found damaged and it was possible to three different broods, settiiig at three different salvage about 50 spat only which were again periods. The next measuriment of the spat measured and the experiment was continued was taken on 21st December 1987, after a lapse from that day onwards considering ihe sample of 35 days. It is seen fiom the histogram as a fresh one. Spat belonging to both the (Fig. 1 A2) that the mode at 30-35 rata seen on batches were measured at periodical intervals. 16th November 1987 has moved to 35-40 mm and the other two modes have merged and Rate of growth of oysters has been studied formed a single mode at 15-20 mm. The next by earlier workers using different methods. histogram dated 29th February 1988 (Fig. 1 A3) Some have followed the length frequency shows two modes at 45-50 mm and 25-30 mm method by examining the random samples and the subsequ nt one dated 3rd April (Herdman, 1903; Devanesan and Chidambaram 1988, after a lapse of 34 days, shows the modes 1956). Some others have tried to interpret at 50-55 mm and 30-35 cam fFig. 1 A4). The the growth, using the growth rings on the measurement taken on 7th July 1988 (Fig. 1 A5) shells (Ghokhale et al., 1954; Narayanan and after 95 days, shows the two modes at 55-60 mm Michael, 1968; Pandya, 1975). A few others and 45-50 mm and also shows a ttiird mode have taken the periodic measurements of the at 35-40 mm. The next reading taken on same oysters kept in sandwich-type frame nets 20tii October 1988 (Fig. 1 A6) after an interval or cages (Chellam, 1978 ; Appukuttan, 1987). of 105 day, shows the modes at 60 65 mm and Growth rate was determined by the size 45-55 mm. As the cage was damaged, all the frequency method. The greatest distance from oysttrs were lost and the experiment was the hinge to the ventral margin of the valves terminated. (DVM) was taken as the length, the antero. posterior measurement as width, the total The seed oysters measuring 5-10 mm on length of the hinge as the hinge length and 16th November 1987 have grown to 25-30 mm the maximum distance between the two valves by 29th February 1988 after a period of 105 as shell depth or thickness. Although the idea days. They attained a size of 35-40 mm on was to take the measurements at regular 7th July 1988 after a total p. riod of 234 days. intervals, due to various reasons it was found Within a period of 339 days, they were all in diflBcult, but at the same time they were taken the size range of 45-55 mm group.
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