Triploidy induction by cold shock in the South American catfish, Rhamdia quelen (Siluriformes) (Quoy & Gaimard, 1824)

The catfish Rhamdia quelen (Siluriformes: Pimelodidae) has been widely produced for human consumption in the Southern and South-eastern Brazil, Argentina and Uruguay. Therefore, studies have been conducted to obtain a greater knowledge of its biology and production improvement, including its growth and food conversion which are compromised by the precocious sexual maturation, interfering with somatic growth. Thus, the possible use of sterile triploids is an interesting option for its culture. The best parameter for cold shock triploidy induction was achieved at 4 °C, 3 min after fertilization for 20 min resulting in 97.9 ± 1.16% of triploid fish. This cold shock conditions resulted in a survival rate of 65.4 ± 5.34%. The nucleoli staining with silver nitrate (AgNO3) proved to be a practical and efficient tool to investigate the ploidy of the animals from the treatments. The Nucleolar Organizer Region (NOR) is located on one chromosome per haploid set at a secondary constriction.