ELECTROPHORETIC ANALYSIS OF TILAPIA
FROM THE DUSIT PALACE STOCK,
Institute of Aquaculture, University of Stirling
Programme for the Development of Pond Management Techniques
and Disease Control (DoF - UNDP/FAO THA/75/012)
National Inland Fisheries Institute
The “Programme for the Development of Pond Management Techniques and Disease Control (THA/75/012)” was implemented in Thailand during 1979–82 as a joint project by the Department of Fisheries (DOF) and UNDP/ FAO. The purpose of the project was to improve DOP support services for Clarias farming through strengthening:
the skills of Fisheries staff in aquaculture disciplines such as disease diagnosis and treatment, pond management and extension,
the research on solutions for problematical aspects of Clarias culture,
the system of relaying problems from the farms to DOF and of transferring improved technologies, and
the equipment and facility base of DOF for working on aquaculture problems.
Although the UNDP/FAO participation was structured to terminate in August 1981, DOF committed continuation of the project to at least August 1982.
This report is one of several Working Papers prepared on various aspects of the project. A list of titles of reports completed in the series is annexed.
Inquiries concerning the subject matter of any particular report should be directed to the author,
c/o The Director
National Inland Fisheries Institute
Kasetsart University Campus
Bangkhen, Bangkok 9
Recent studies by fish genetic experts from Canada and the U.S.A. indicated the prospect of increasing aquaculture production through improving the performance of some stocks by genetic management. Particular note was made that improvements are wanting in tilapia, common carp, Macrobrachium and Clarias stocks. In response, the Thai Department of Fisheries implemented a fisheries genetics program that would create a genetics core staff while initiating work on the genetic management of some of the stocks. This introductory work was confined to tilapia and common carp since there were ample literature references on the genetic management of these species which could help direct the early phases of the Thai program.
Amongst the initial requirements of Thailand's program was a determination of the genetic purity of brooders used to generate seed fish for aquaculture. Samples of the base brood stock of tilapia in Thailand were thus submitted to the Institute of Aquaculture, University of Stirling, for genetic assessment. This work was executed under the “Programme for the Development of Pond Management Techniques and Disease Control (DoF-UNDP/FAO THA/75/012)” and the attendant report presents the preliminary results of the analysis by the University of Stirling.
The first tilapia, Tilapia mossambicus, were introduced to Thailand in the 1950's. Undesirable features of this species were soon revealed and further use of T. mossambicus is aquaculture and in the stocking of public waters was discontinued by the Department of Fisheries. The extent that the species spread or established population pools was, however, unknown.
Another introduction of tilapia, reputedly Sarotherodon (= Tilapia) niloticus, was made in 1965 when 50 fish were presented to His Majesty King Bhumiphol of Thailand by the Crown Prince Akihito of Japan. These fish were placed in discrete ponds within the grounds of the Dusit Palace, Bangkok. The Department of Fisheries assumed management of this stock which was cultured as brood for the continuing generation of fry. Several million fry have since emerged from this source and have been distributed throughout the country. Being in a circumstance which allowed tight control on the integrity of the stock, then the prospect was secure that the stock was reproductively isolated and that it remained genetically the same as provided whatever the species or strain.
Tilapia samples for genetic analysis by the University of Stirling were drawn from the Dusit Palace ponds.
Alex N. Fedoruk
Fisheries Development Adviser
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ELECTROPHORETIC ANALYSIS OF S. NILOTICUS FROM THE DUSIT PALACE STOCK
Preliminary results of an electrophoretic study to determine the genetic purity of tilapia stock held in ponds at the Dusit Palace, Thailand, indicate the species is a relatively pure strain of Sarotherodon (=Tilapia) niloticus Confirmation will be available on the completion of crossing experiments with S. aureus for yielding all male offspring that are scheduled in July - August 1981. The Department of Fisheries, Thailand, is encouraged to ensure the integrity of this unique brood stock.
The Dusit Palace fish have supplied much of Thailand with “Sarotherodon niloticus” and it is now a very important culture species throughout the country. It is therefore of great importance to check the genetic integrity of such a brood stock population. The purpose of this is to assess purity of the stock so that direct comparisons may be made between results obtained on this strain and others in different countries, as well as assessing the possibility of applying genetic husbandry techniques for improving the performance of cultured tilapia including measures such as the production all-male hybrids using this stock.
Morphological characteristics have long been used to discriminate between different fish species. These characters, however, are influenced by the environment and are therefore normally distributed. This means that in closely related species there is often a large overlap in characters being used. However, as hybrids are often intermediate in character those overlapping individuals must be discarded when selecting for broodstock. This is not only wasteful but also unnecessarily reduces the variation present in the species leading to inbreeding.
* Research Lecturer, Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland.
Recently, gel electrophoreses has proved to be an effective tool in taxonomy and species identification. Gel electrophoresis is the separation of protein molecules through a gel matrix under the influence of an electric current, the molecules separating in relation to their ionic charge and molecular weight. When separated, the various enzymes and proteins may be resolved by the use of specific histochemical strains. This technique allows the detection of mutations resulting in a change of charge or quaternary structure, which are manifested as changes in mobility of the particular enzyme band in the gel. This type of mutation occurs at random throughout the genome and new mutations will spread throughout the species range by migration of individuals from the source of the original mutation. Once a population becomes reproductively idolated due to speciation or geographic barriers, these mutations will continue to occur randomly and at a constant rate in both populations. These differences can then be used to differentiate between the populations. Such genetic characters are co-dominant and any differences will be expressed, unlike morphological characteristics. Therefore mobility differences which exist in the pure species will both be expressed in the hybrid. When these differences are studied over a large number of enzyme loci it is possible to draw up an accurate picture of the species evolution.
A sample of 30 tilapia from the lot of the Dusit Palace strain, held at the University of Stirling, was subjected to electrophoretic analyses. Molecular mobility patterns were determined in four enzyme bnads - creative kinase, phosphoglucose isomerose, tetrazolium oxidase and adenosine deaminase. The resulting band patterns were compared with the pre-determined patterns of other S. niloticus and S. mossambicus.
Overall, the patterns in the four enzyme bands of the Dusit Palace samples compare very closely with the known patterns of S. niloticus. Furthermore, the patterns were distinctly different from those of S. mossambicus. Some band features occurred, however, which suggest the presence of unique alleles that can be related to hybridization.
There proved to be three polymorphic loci (two or more alleles) within the Dusit Palace samples. Most pure populations have some polymorphic loci, but excessive variation at any locus might be indicative of hybridization between two species with mobility differences at that locus. One allele in the adenosine deaminase system that also occurs in S. mossambicus was found in two of Dusit Palace fish. This allele has not been found in other S. niloticus populations sampled, although this may be because in wild populations the allele is rare and would only be found if large samples (> 100) were analysed. The allele may be more common in this population due to a sampling error in the original selection of individuals; the rare allele becoming relatively common in the small sample size and then being maintained by breeding within the population.
This seems the most probable explanation as the other unique banding mobilities between S. niloticus and S. mossambicus did not occur in this sample. The other possible explanation is that some other species which I have not yet analysed may have hybridized with the Palace stock, such as S. honorum which could even have occurred in Japan.
It is quite evident that the Dusit Palace tilapia is S. niloticus and that the population appears to be relatively pure, at least in the sample that I received, indicating that the Palace stock of S. niloticus has remained pure and that every effort should be made to see that it continues so. The final test will be the production of 100% male offspring from the hybrid cross between S. aureus male X S. niloticus female, which will be attempted at Stirling when the rest of the fingerlings sent for analysis have matured. If this cross proves successful, then the Palace stock will be a useful source of broodstock for crossing purposes within Thailand. Such work would be carried out with a range of different species to show which hybrid proved the most useful under local conditions. If such hybridisation experiments were to be tried this would entail rigid management practice to ensure that the broodstock did not back cross with the hybrid. However, routine annual checks could be carried out on the broodstock by starch gel electrophoresis using samples of muscle removed by a biopsy technique developed at Stirling and elsewhere.
“Dear Dr. Fedoruk,
This is an interim report on the analysis of the Dusit Palace tilapia. The final report with actual allele frequencies and breeding data will be produced as soon as the remaining fish are mature and can be used in crossing experiments which are scheduled for the coming July-August period (1981).
The Programme for the Development of Pond Management
Techniques and Disease Control
THA/75/012/WP 1 Report on Aquaculture Training Undertaken at the International Center for Aquaculture, Auburn University, U.S.A. Chanchai Sansrimahachai
THA/75/012/WP 2 Third Semi-Annual Report (Sept. 1/80-Feb. 28/81) of Progress on the “Programme for the Development of Pond Management Techniques and Disease Control (DoF-UNDP/FAO THA/75/012)”. Alex N. Fedoruk
THA/75/012/WP 3 Management in Clarias Culture, Thailand. James Muir
THA/75/012/WP 4 Collecting Clarias Fry from Natural Waters. Montree Muangboon
THA/75/012/WP 5 Preliminary List of Diseases of Cultured Clarias in Thailand. National Inland Fisheries Institute, Thailand and Institute of Aquaculture, Stirling, Scotland.