Effect of Cold Shock on Larval Viability and Tetraploid Percentage of Asian Redtail Catfish, Hemibagrus nemurus (Valenciennes, 1840)

This study aimed to evaluate the effects of cold shock time and temperature on larval viability and the formation of tetraploid Asian redtail catfish, Hemibagrus nemurus (Valenciennes, 1840). A completely randomized factorial design was used with 2 factors, shock time after fertilization (AF) which consisted of 5 levels (26th, 27th, 28th, 29th, and 30th min AF) and shock temperature with 3 levels (6, 8, and 10 °C). Furthermore, each group carried out in 3 replicates, and the observed parameters including the percentage of tetraploid fish, fertilization rate, hatching, larval survival, and percentage of abnormal larvae recorded. The identification of tetraploid individuals was based on the analysis of the total nucleoli, erythrocyte size, and DNA content by flow cytometry. The results showed that cold temperature shock had an effect on hatching rate, survival rate, and the number of abnormal larvae (p < 0.05) but had no effect on egg fertilization rate (p > 0.05). The highest hatching rate was obtained in temperature shock treatment at 10 °C (60.06 ± 0.85 %), while the highest survival was obtained in temperature shock treatment at 10 °C (68.33 ± 1.38 %). Moreover, the shock time AF and temperature shock treatments influenced the formation of tetraploid the Asian redtail catfish (p < 0.05). Shock treatment at 28 min AF with a shock temperature of 6 °C for 3 min produced the highest tetraploid percentage (78.33 ± 1.67 %, p < 0.05). Tetraploid the Asian redtail catfish had a maximum number of 4 nucleoli per cell, while diploid catfish had a maximum of 2. The erythrocyte and nucleus volumes were 98.26 and 99.51 %, respectively, which were larger than those of the diploid the Asian redtail catfish. Furthermore, the DNA content in the tetraploid individuals was twice that in the diploid individuals. Thus, cold temperature shock at 6 °C for 3 min to the 28-minute-old embryos to produce a tetraploid the Asian redtail catfish is recommended. HIGHLIGHTS This article focuses on the application of cold shock to the formation of tetraploid Asian Redtail Catfish Cold shock in embryos can produce tetraploid Asian Redtail Catfish Tetraploid in Asian Redtail Catfish is an intermediate process to produce triploid Asian Redtail Catfish The success of tetraploid induction of Asian Redtail Catfish is affected by shock time and shock temperature GRAPHICAL ABSTRACT