Fig. 11. Mean of otolith Sr/Ca ratios from core to edge in four locations show all marble goby individuals' survived in freshwater (a), but Kimanis river has marble goby, which early life in brackishwater then shift into freshwater (b). The number of samples, n.
Table 12. Fluctuation intervals in otolith of marble goby from four locations
Locations Fluctuation Intervals (.um)
21-40 41-60 61-100 > 101
Ipoh pond (WM) 9 4 4 3
Kundang river (WM) 9 4 4 3
Kuching pond (EM) 6 4 7 2
Kimanis river (EM) 11 2 0 7
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-3.4 Discussion
Shift in water salinity
This study is the first report of marble goby otolith Sr/Ca ratios analysis to investigate the fish individual's habitat salinity in WM and EM. Although SalO showed exceptional otolith Sr/Ca ratios in Kuching pond, the Sr/Ca ratios showed its life history in constant salinity habitat, where might be no changes in water salinity and no shift in water salinity during growth. As mentioned in Chapter 2, the samples from Kuching and Ipoh were collected from several freshwater ponds in both locations due to the small number of samples in each pond. Thus, there is a possibility that this SalO is from different pond with other samples in Kuching pond. Besides of salinity, the growth patterns might influence the Sr/Ca ratios as well. The random growth of marble goby in Kuching pond, which revealed by the results of spectral analysis, could explain the erratically otolith Sr/Ca ratios in Sal 0.
Marble goby is regarded as a freshwater fish; however, this study reveals two marble goby individuals in Kimanis river of EM, Kim8 and KimlO were probably survived in brackishwater at early life, and then shift into freshwater. This inference is based on the results of Senoo et al. (2008) that the marble goby larvae in Sabah (EM) cannot survive in high salinity water, but the best survival in the optimum salinity, 10 psu. In addition, there is no scientific report of the salinity level corresponding to the otolith Sr/Ca ratios for marble goby. Thus, the exact salinity level in the wild cannot be identified in this study.
The other marble goby of Kimanis river lived their whole lives in freshwater only. It shows a possibility that two types of marble goby are existed, first type is surviving in freshwater only; second type is surviving in brackishwater at early life and then shift into freshwater. This could be one of the reasons to explain the marble goby larval survival in Sabah of EM was the best in 10 psu water, which has been reported by Senoo et al. (2008). Probably the broodstock, which was used for seed production, was the second type. Therefore, it is advised that the seed production of marble goby in
Sabah should be carried out carefully if the broodstock are collected from the wild.
Although succeeded to discover some marble goby shift in water salinity in the Kimanis river, the exact and absolute time of shifting is still unknown. Fish otoliths accrete layers of calcium
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carbonate and gelatinous matrix throughout their lives (Degens et al. 1969; Gauldie and Nelson 1988).
The accretion rate varies with growth of the fish, usually less growth in winter and more in summer in temperate zone, which results in the appearance of opaque and translucent rings respectively. Thus, it is possible to determine the age of the fish in years by counting the rings (Campana and Thorrold 2001 ). However, for the tropical fish such as marble goby, there are no obvious opaque and transparent rings in otolith as fishes in temperate zone. In future, more rigorous studies are recommended to estimate the age of marble goby based on the otolith rings counting, and to investigate the larval otolith on which daily rings can be detected. It will reveal the exact age of the marble goby during the shift of water salinity in the wild. Consequently contribute to the timing of salinity change, if the 10 psu water is used initially for the marble goby larval rearing in the hatchery.
Besides, mtDNA results in Chapter 2 revealed both Kim8 and KimlO in Kimanis river, which showed shift in salinity from brackishwater enter into freshwater, had the same distinct haplotype of Hap-14, and this distinct haplotype can be found in Sabah indigenous population only. However in this study, Hap-14 was detected as well in Kim2 and Kim5, which showed life history in freshwater habitat only. According to the theory of maternal inheritance of mtDNA, Kim2, Kim5, Kim8 and KimlO were from the same maternal ancestor. Thus, the maternal ancestor with Hap-14 might have the genetic factor of possibility to survive in both freshwater and brackishwater at early life in the wild (Taylor 1990). However, Senoo et al. (2008) reported that all Sabah marble goby larvae only survived in 10 psu water. This can be explained by the paternal genetic contribution mating with the female. The way to determine the genotype, which affects to the salinity tolerance, is unknown, however, the mating might has a possibility to produce three types of offspring, which could survive in freshwater only, survive in brackishwater only, and able to survive in both. This inference could explain the survival in different salinity even the fish have the same haplotype.
Growth patterns
As mentioned before, the accretion rate of otolith varies with fish growth, and then results different fluctuation rate in otolith. These relative widths and intervals results the pattern of periodical growth marks, which differ between species and populations and so does the ease of their
62
-identification and interpretation (Lombarte et al. 2003). The accretion rate is often linked to environmental changes in exogenous variables such as feeding, but the transition timing may change during development and with geographical distribution (Wright et al. 2002). Endogenous variables may interact with exogenous factors as well that lead to more variable patterns in otolith.
The spectral analysis in this study showed both the Ipoh pond and the Kundang river marble goby in WM had same growth patterns. In other words, they were probably living under similar environment or habitat in west of WM, even though they are genetically different populations (based on the results in Chapter 2). On the other hand, Kuching pond and Kimanis river marble goby in EM have their own different growth patterns respectively. The marble goby in Kuching pond are always dwelling in enclosed freshwater pond. Compared to the marble goby in Kuching pond, Kim8 and Kim 10 in Kimanis river had been migrated from brackish water to freshwater and, which need to consume more energy for the osmoregulation. Consequently might affect the unique growth patterns in the otoliths in the Kimanis river.
Coupling of the population genetics and otolith Sr/Ca ratios analysis succeed to discover the population differentiations of marble goby with migration-patterns. The population genetic study of marble goby in Southeast Asia revealed the population differentiation or divergence is due to the widely geographical distributions (Chapter 1) and the geographical features (Chapter 2). The otolith Sr/Ca ratios analysis showed the early life history of fish individual in salinity habitat is different even within the same population, as discovered in Kimanis river. This finding has an important implication of a careful broodstock management of marble goby for seed production in the hatchery.
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Acknowledgments
First of all, sincere gratitude is extended to my supervisor, Assoc. Prof. Dr. Kato Keitaro for his continuously encouragement and dedicated guidance throughout my three years study. My special appreciation extended to Prof. Dr. Senoo Shigeharu for his logistically supports on my study.
My special thanks also go to Prof. Dr. Murata Osamu and Prof. Dr. Miyashita Shigeru for their kind encouragement. My grateful thanks to Prof. Dr. Sakamoto Wataru and Dr. Tsuda Yuichi for their teaching in otolith sample preparation and interpreting data of otolith analysis. Special thanks to Dr. Nakagawa Yoshizumi and Dr. Tsunemoto Kazunobu for their encouragement and logistically supports in my experimental designs. Thanks also to all the researchers and students in Shirahama Fisheries Laboratory for their support as well as their commitment and suggestions during the discussion sessions.
Many people have generously given their help with this study by providing specimens or by making collection data available. My appreciations to the director of Borneo Marine Research Institute (BMRI), Prof. Dr. Saleem Mustafa and the former director, Prof. Dr. Ridzwan A. Rahman for the approval to conduct my experiments in the hatchery. I thank all the staff of the BMRI Fish Hatchery, for their cooperation in the experiments. I am greatly indebted to Mr. Yusuke Takeuchi and Mr. Yusuke Sato of Shimakyu Co. Ltd. in Thailand, Mr. Lim Kai Siang of Aquacliq in Selangor and Mr. Thian Hai Chung of Honey Aquaculture in Kuching for providing the fin samples and the transportation to conduct the sampling trips. Also thanks to Mrs. Chun Kia Huey and Dr. Muhammad Darwis for their help with the sampling from Vietnam and Indonesia, respectively. Never forget to thank Assoc. Prof. Dr. Umino Testuya in Hiroshima University for lending me the standards for the calibration of otolith analysis.
This dissertation and work has been generously supported by the scholarship from Kinki University and Ministry of Education, Culture, Sports, Science and Technology, Japan, under the Global COE program "International Education and Research Center for Aquaculture Science of Bluefin Tuna and other Cultured Fish". I am extremely grateful to the foundation and to all its program officers and staff.
64
-Thank you very much to my beloved family for their understanding and moral support during my PhD study in Japan. Lastly, I thank to the mighty God for His bless and strength that kept me persevere until succeed.
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71
-Summary
The marble goby Oxyeleotris marmoratus belongs to the suborder Gobioidei in the order Perciformes. It has partial flattened body with snake-like head, symmetrical pattemihg on the dorsal surface and rounded, outstretched round pectoral fin, two dorsal fins, rounded caudal fin and separated pelvic fins. It is a popular freshwater fish in Southeast Asia for its fine texture and delicious taste. In the wild, it feeds on small fish, shrimp, molluscs and crustaceans. It can grow to a maximum size of approximately 65 cm standard length. Fish farmers would like to culture the marble goby, but the seed supply is still mainly dependent on natural sources. In 2008, the seed production of marble goby has been succeeded in Sabah of East Malaysia. Although it is a freshwater fish, 10 psu diluted seawater is the best for the larval survival of marble goby in Sabah. It showed the possibility of different populations is existed in Southeast Asia. Thus, three experiments were conducted to better understanding of its population structure and early life history in salinity in nature would aid more effective broodstock management in the hatchery for seed production.
Chapter 1
This study was conducted to investigate the population structure of the marble goby in Southeast Asia. A total of 85 fin samples were collected from 3 regions (the mainland, the peninsula, and the islands) for mitochondrial DNA (mtDNA) analysis. Sampling locations that were geographically close were pooled and treated as a single population. Partial mtDNA control regions were amplified, sequenced, and analyzed. Fourteen haplotypes were detected among all the samples.
Hap-5 was the most widespread haplotype among the six populations, comprising of 29.4% of all samples. Both the non-significant values of Tajima's D and Fu's Fs suggested that all 6 populations were at equilibrium. Analysis of molecular variance (AMOV A) revealed significant differences among and within populations, and no variance was due to regional site (Fer= - 0.1498, P>0.05). In pairwise comparisons of Fsr, Ayutthaya, Dong Nai and Sabah showed significant values (P<0.05) between the all populations. The non-significant values of Fsr showed that Sarawak, Indonesia, and West Malaysia are less genetically different. This suggests that the marble goby in Ayutthaya, Dong
-