Status Genetik dan Persilangan Ikan Nila Merah Varietas Sukabumi, Thailand, dan Taiwan

Abstract

Ikan nila merah lokal, varietas Sukabumi telah mengalami penurunan kinerja pertumbuhan yang diperkirakan akibat silang dalam karena jumlah induk yang terbatas dan penggunaan induk secara terus-menerus dalam waktu lama sehingga mengalami reduksi ragam genetik. Dalam upaya memperbaiki mutu genetik ikan nila lokal varietas Sukabumi, maka perlu dilakukan introduksi ragam genetik melalui kegiatan persilangan dengan sumber genetik dari varietas lain yang berbeda. Persilangan antar varietas dengan perbedaan ragam genetik pada tingkat kekerabatan tertentu efektif dapat meningkatkan mutu genetik dan performa produksi melalui keunggulan heterosigot dan pengkayaan ragam genetik populasi. Penelitian ini bertujuan untuk: (1) Menganalisis tingkat keragaman dan kekerabatan genetik antar varietas nila merah lokal varietas Sukabumi dengan varietas nila introduksi Thailand, dan Taiwan berbasis marka gen mtDNA COI dan analisis Random Amplified Polymorphic DNA (RAPD), (2) Mengevaluasi performa produksi antar varietas dan hasil persilangan antar varietas (Sukabumi, Thailand, Taiwan) meliputi pertumbuhan, sintasan, body shape, dan karakter pigmentasi black blotching. Ikan nila varietas Sukabumi diperoleh dari koleksi induk Balai Besar Perikanan Budidaya Air Tawar (BBPBAT) Sukabumi (S), yang merupakan fasilitas budidaya perikanan milik negara di Jawa Barat, Indonesia. Ikan nila varietas Thailand (L) dan Taiwan (W) merupakan varietas introduksi pada tahun 2022 yang berasal dari Nam Sai Farm, salah satu fasilitas budidaya ikan nila komersial di Thailand. Setiap varietas terdiri dari 30 betina (?) dan 12 jantan (?) yang berukuran panjang 29-32 cm dan berat 285-300 g. Induk dipilih berdasarkan status kesehatannya. Tingkat keragaman genetik dianalisis dengan teknik RAPD dan kekerabatan genetik antar varietas dikonfirmasi berdasarkan analisis sequencing mtDNA COI. Persilangan dilakukan secara resiprokal tiga varietas ikan nila (Sukabumi, Thailand, dan Taiwan) sehingga terdiri dari 9 kombinasi pada pemijahan ikan. Pemijahan ikan dilakukan pada hapa pemijahan dengan perbandingan 10 ?: 4 ?. Sebanyak 9-unit bak beton (2×2×3 m) digunakan sebagai wadah untuk pendederan benih, sedangkan untuk pembesaran digunakan 27 kolam terpal bulat dengan diameter 4m dan tinggi 1m (volume 10 m3). Larva diberi pakan berupa pakan bubuk berprotein 40% dengan cara pakan buta hingga berukuran 3-5cm selama 3 minggu. Selanjutnya, benih dipindahkan ke kolam bioflok terpal bulat dan dipelihara sampai 130 hari, serta diberi pakan berupa pelet apung berprotein 28% sebanyak 3% biomassa perhari dengan frekuensi 2 kali sehari. Saat ikan mencapai ukuran 61-125 gram, kemudian diberi pakan pelet komersial terapung berprotein 28% sebanyak 2% biomassa perhari, sesuai dengan prosedur pemeliharaan ikan nila sistem bioflok. Hasil analisis keragaman genetik dan kekerabatan genetik berdasarkan analisis sequencing mtDNA COI, serta performa reproduksi dievalusi secara deskriptif. Data kuantitatif berupa pertumbuhan dan performa produksi dianalisis sidik ragam dan diuji lanjut Tukey dengan selang kepercayaan 95%. Karakter morfologi black blotching, luas pigmen, dan truss morphometrics dianalisis non parametrik, dengan uji lanjut Mann-Whitney dengan selang kepercayaan 95%. Sedangkan, dimorfisme seksual dianalisis dengan uji t-test dengan selang kepercayaan 95%. Data diolah menggunakan software Statistical Program Software System (SPSS) versi 26. Analisis mtDNA COI ikan nila Sukabumi, Thailand dan Taiwan menunjukkan kekerabatan genetik dengan varietas Filipina dan membentuk kluster terpisah antara varietas Sukabumi dengan Thailand dan Taiwan. Hasil elektroforesis target sekuens mtDNA COI ikan nila Sukabumi, Thailand dan Taiwan memunculkan pita berukuran sekitar 700 bp. Tingkat keragaman genetik berdasarkan analisis RAPD menunjukkan varietas ikan nila Sukabumi lebih rendah (heterozigositas He=0,128; polimorfisme 41,67%) dibanding Thailand (He=0,262; Poly 87,5%) dan Taiwan (He=0,149; Poly=41,67). Persilangan nila Sukabumi dengan Thailand (SL/LS) menunjukkan peningkatan heterozigositas 52,3-70,3% dan polimorfisme 75%. Namun, semua persilangan memiliki performa reproduksi yang rendah serta kelangsungan hidup larva (TKH 6-20%) yang lebih rendah dibandingkan varietas lokal (TKH 69,34%) dengan jumlah larva (2.338±1.423 ekor). Persilangan nila Sukabumi dengan Thailand (SL/LS) meningkatkan laju pertumbuhan spesifik (LPS 4,28%/hari) dengan heterosis 11,84%, tetapi kelangsungan hidup ikan pada tahap pembesaran mengalami penurunan hingga 54,56%. Sebaliknya, persilangan nila Sukabumi dengan Taiwan (SW/WS) meningkatkan biomassa dengan heterosis 22,48% dengan laju pertumbuhan spesifik 7,01%/hari. Analisis truss morphometrics pada persilangan WS menunjukkan bahwa variasi pada tinggi badan (B3), yang menjadi pemisah dengan perilangan yang lain. Nilai ekstrem F1 dan F2 terutama dipengaruhi oleh jarak B3 dan D1, di mana tinggi badan sering dijadikan seleksi terhadap produktivitas fillet. Warna merah intensif (61-100%) menurun pada semua progeni hasil persilangan (55-96%), dan mengurangi black blotching hingga 100% (pada SL). Temuan ini berguna dalam menyusun strategi pemuliaan selektif untuk memanfaatkan keunggulan genetik ikan nila introduksi dan meningkatkan potensi adaptasi lokal. Penelitian ini mengkonfirmasi varietas nila merah Sukabumi memiliki keragaman genetik rendah, sedangkan varietas Thailand dan Taiwan memiliki keragaman lebih tinggi serta kekerabatan dekat dengan varietas nila Filipina. Persilangan nila Sukabumi dengan varietas Thailand lebih efektif meningkatkan keragaman genetik dan meningkatkan laju pertumbuhan tetapi menurunkan tingkat kelangsungan hidup, sedangkan persilangan dengan varietas nila Taiwan meningkatkan kelangsungan hidup dan biomassa. Persilangan nila Sukabumi dengan varietas nila Thailand dan Taiwan tidak mempengaruhi karakter pigmentasi merah tetapi bisa mengurangi tingkat black blotching.

The local red tilapia variety Sukabumi has experienced a decline in growth performance, which is estimated to be due to inbreeding because of the limited number of parents and the continuous use of parents for a long time, resulting in a reduction in genetic diversity. To improve the genetic quality of local tilapia of the Sukabumi variety, it is necessary to introduce genetic diversity through crossbreeding activities with genetic sources from other varieties. Crossbreeding between varieties with differences in genetic diversity at a certain level of kinship can effectively improve the genetic quality and production performance through heterozygous advantages and enrichment of genetic diversity in the population. This study aimed to: (1) analyze the level of diversity and genetic kinship between local red tilapia varieties of Sukabumi variety with introduced tilapia varieties of Thailand and Taiwan based on mtDNA COI gene markers and Random Amplified Polymorphic DNA (RAPD) analysis, and (2) evaluate the production performance between varieties and cross-breeding results between varieties (Sukabumi, Thailand, Taiwan) including growth, survival, body shape, and black blotching pigmentation characteristics. The Sukabumi variety of tilapia was obtained from the parent collection of the Balai Besar Perikanan Budidaya Air Tawar (BBPBAT) Sukabumi, which is a state-owned fishery cultivation facility in West Java, Indonesia. Thailand (L) and Taiwan (W) tilapia varieties are introduced in 2022, originating from Nam Sai Farm, a commercial tilapia cultivation facility in Thailand. Each variety consists of 30 females (?) and 12 males (?) measuring 29-32 cm in length and weighing 285-300 g. Broodstock was selected based on health status. The level of genetic diversity was analyzed using RAPD, and genetic kinship between varieties was confirmed based on mtDNA COI sequencing analysis. Crossbreeding was carried out reciprocally with three varieties of tilapia (Sukabumi, Thailand, and Taiwan), which consisted of nine combinations for fish spawning. Fish spawning was carried out in the spawning hapa with a ratio of 10 ?: 4 ?. Nine concrete tanks (2×2×3 m) were used as containers for the seed nursery, while 27 round tarpaulin ponds with a diameter of 4m and a height of 1 m (volume 10 m3) were used. The larvae were fed 40% protein powder feed by blind feeding for 3 weeks until they were 3–5 cm in size. Furthermore, the seeds were transferred to a round tarpaulin biofloc pond and maintained for up to 130 days, and fed 28% protein floating pellets (as much as 3% biomass per day) at a frequency of 2 times a day. When the fish reached a size of 61-125 grams, they were fed commercial floating pellets with 28% protein, as much as 2% of biomass per day, according to the tilapia maintenance procedure using the biofloc system. The results of genetic diversity and kinship analyses based on COI mtDNA sequencing and reproductive performance were evaluated descriptively. Quantitative data in the form of growth and production performance were analyzed using variance analysis and further tested using Tukey’s test with a 95% confidence interval. The morphological characteristics of black blotching, pigment area, and truss morphometrics were analyzed non-parametrically using a Mann-Whitney test with a 95% confidence interval. Meanwhile, sexual dimorphism was analyzed using the t-test with a 95% confidence interval. Data processing was performed using the Statistical Program Software System (SPSS) version 26. Analysis of mtDNA COI tilapia from Sukabumi, Thailand, and Taiwan showed a genetic kinship with the Philippine variety and formed a separate cluster between the Sukabumi variety and Thailand and Taiwan. Target electrophoresis of mtDNA COI tilapia from Sukabumi, Thailand, and Taiwan produced a band measuring approximately 700 bp. The level of genetic diversity based on RAPD analysis showed that Sukabumi tilapia varieties were lower (heterozygosity He=0,128; polymorphism 41.67%) than those in Thailand (He=0,262; Poly 87,5%) and Taiwan (He=0,149; Poly=41,67). Crossbreeding of Sukabumi tilapia with Thailand (SL/LS) showed an increase in heterozygosity of 52,3-70,3% and polymorphism of 75%. However, all crossbreeds had lower reproductive performance and larval survival (TKH 6-20%) compared to local varieties (TKH 69,34%) with the number of larvae (2,338 ± 1,423). Crossbreeding of Sukabumi tilapia with Thailand (SL/LS) increased the specific growth rate (LPS 4,28%/day), with a heterosis of 11,84%, but fish survival at the rearing stage decreased to 54,56%. In contrast, crossbreeding of Sukabumi and Taiwan tilapia (SW/WS) increased biomass with a heterosis of 22.48% and a specific growth rate of 7,01%/day. Truss morphometric analysis of WS crosses showed variations in body height (B3), which was separated from other crosses. The extreme values of F1 and F2 were mainly influenced by the distance between B3 and D1, where body height is often used to select fillet productivity. Intensive red color (61-100%) decreased in all crossbred progenies (55-96%) and reduced black blotching by 100% (in SL). These findings are useful for developing selective breeding strategies to utilize the genetic advantages of introduced tilapia and increase the potential for local adaptation. This study confirmed that the red Sukabumi tilapia variety has low genetic diversity, whereas the Thailand and Taiwan varieties have higher diversity and are closely related to the Philippine tilapia variety. Crossing Sukabumi tilapia with Thailand varieties is more effective in increasing genetic diversity and increasing growth rate but reducing survival rate, while crossing with Taiwan tilapia varieties increases survival and biomass. Crossing Sukabumi tilapia with Thailand and Taiwan tilapia varieties does not affect the red pigmentation character but can reduce the level of black blotching.