Lysozymes play an important role in the first line of defense in fish and potentially used as an immunity status biomarker and immune responses evaluation in fish, which often found in two types, i.e. chicken-type and goose-type (c- and g-type, respectively). To recent, the information related to the sequences and the expression analysis of the c- and g-type lysozyme genes in African catfish is still limited. In the present study, we report a partial cloning and mRNA expression analysis of c-type and g-type lysozymes in African catfish Clarias gariepinus. We have successfully cloned and partially identify the c-type, and g-type lysozyme genes of C. gariepinus, which consist of 594 and 560 of coding sequences, respectively. Catalytic and other conserved residues were identified by multiple sequences alignment and they showed high similarity with other teleost fish species. mRNA levels of the genes were analyzed by using qPCR method and their expressions in the spleen, liver, and head kidney were rapidly modulated after Aeromonas hydrophila injection, with different patterns were observed in each organ. These results confirmed that c- and g-type lysozymes played an important role in non-specific immunity against A. hydrophila infection. This study provided valuable information that can be used to understand the African catfish immune systems for better disease and stress management in C. gariepinus culture.Keywords: lysozymes, gene identification, gene expression, bacterial infection, African catfish ABSTRAKLisozim berperan dalam sistem pertahanan dini pada ikan dan sangat potensial digunakan sebagai marka status imunitas dalam evaluasi respons imun. Lisozim umum ditemukan dalam dua tipe pada ikan: tipe-ayam (tipe-c) dan tipe-angsa (tipe-g). Informasi terkait sekuens gen dan ekspresi gen kedua tipe lisozim pada ikan lele dumbo sangat terbatas. Pada penelitian ini, kami melaporkan kloning gen secara parsial, dan analisis ekspresi gen dari kedua tipe lisozim pada ikan lele dumbo C. gariepinus. Sekuens parsial gen lisozim tipe-c dan tipe-g yang berhasil diidentifikasi adalah sepanjang 594 dan 560 pasang basa. Situs katalitik dan residu khas memiliki tingkat kesamaan yang tinggi dengan spesies ikan yang lain. Analisis mRNA dilakukan dengan metode quantitative PCR (qPCR). Ekspresi kedua gen di jaringan ginjal depan, limpa, dan hati dengan cepat terinduksi pasca infeksi bakteri A. hydrophila dengan pola yang berbeda. Hasil ini menunjukkan bahwa lisozim tipe-c dan tipe-g memiliki peran yang sangat penting dalam sistem imun ikan lele dumbo terhadap infeksi A. hydrophila. Penelitian ini menghasilkan informasi penting yang dapat digunakan untuk mempelajari sistem imun ikan lele dumbo dan sebagai acuan dalam penanganan dan manajemen penyakit pada budidaya ikan lele dumbo.Kata kunci: lisozim, identifikasi gen, ekspresi gen, infeksi bakteri, ikan lele dumbo

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In order to lower the fish mortality during transportation, the chopped banana stem (BS) was added during the African catfish transport procedure. The fish were packed in plastic bags with a density of 100 fish in 1.5 L water. The chopped BS was added into the plastic bags with different concentrations: 0 (control), 5, 10, and 15 mg L−1. The fish were transported for 5 hours. After transportation, the fish, together with the added chopped BS, were distributed into glass tanks and acclimated for 24 h. After 24 h, the results showed that the BS treatments had lower cumulative mortality compared to the control with the lowest mortality was observed at the 15 mg L−1 concentration (p<0.05). The BS treatments also increased the antioxidant defence and the immune status of the fish thus might be responsible for the reduced mortality.

Abstract. Authors. 2020. Short Communication: Single nucleotide polymorphism in C-type lysozyme gene and its correlation with Aeromonas hydrophila resistance in African catfish Clarias gariepinus. Biodiversitas 21: 311-317. The chicken-type lysozyme (LYSC) gene has been demonstrated to play important roles in the fish protection system against bacterial infection. In this present study, we aimed to identify the single nucleotide polymorphism (SNP) within the LYSC gene of African catfish Clarias gariepinus and its possible association with Aeromonas hydrophila resistance, a major pathogenic bacterium in African catfish. The gDNA of the African catfish LYSC coding sequence was 1559 bp long, comprising of four exons and three introns. Six SNPs were identified in African catfish LYSC, namely SNP1-6. After the A. hydrophila challenge, we regarded the surviving individuals after the infection as the resistant group and the dead fish as the susceptible group. High-resolution melting (HRM) analysis on SNP2 revealed that the allele frequencies of TT, CC, and TC were of 27.78%, 5.55%, and 66.67% in the resistant group, while the frequencies of TT, CC, and TC were 16.67%, 27.78%, and 55.55% in the susceptible group, respectively. The expression of LYSC and other immune-genes in the resistant group was also higher in the liver, head kidney, and spleen. These results indicated that the LYSC gene might play an essential role in bacterial resistance, and the SNP2 within the LYSC gene may be associated with the resistance to A. hydrophila in African catfish.