Comparative Growth of Diploid and Triploid Asian Catfish Clarias macrocephalus in Thailand

Wild caught Asian catfish were spawned manually following HCG injection, and a portion of the eggs were subjected to cold-shock at 4 C for 15 min within 2-min post-fertilization. Nuclear diameter measurements of cold-shocked fish revealed that 96% were triploids (3N), while non-shocked fish were all diploids (2N). During larval and fry culture (first 26 d), triploid fish mortality was =50%, while diploid mortality was =25%. Following 8-mo culture in tanks at three stocking densities, triploid fish survival was significantly greater ( P < 0.05), than diploids, with 84.0% and 57.3%, respectively. Triploid live weight was also significantly greater than diploids, with 69.2 and 45.9 g averages, respectively. Ninety-two percent of diploids had welldeveloped gonads after 8 mo; whereas none of the triploids had mature gonads. Gonads were undifferentiated with 31% of the triploids. These sexually undifferentiated fish had greater growth rates than male or female triploids, and greater growth than all diploids. Carcass weight (gutted) of triploids was 95.8% of live weight, compared with 92.5% for diploids. Lastly, triploids had very few deformities compared with diploids, with 1.3% and 17.6%, respectively. Deformities included curved spines, and humped backs just posterior of the head.     

Ethidium Bromide Nuclear Staining and Fluorescence Microscopy: An Alternative Method for Triploidy Detection in Fish

Abstract.– Erythrocyte nuclei from normal diploid (2N) and cold-shocked triploid (3N) Asian catfish Clarias macrocephalus were comparatively stained with fluorescent stain, ethidium bromide and with a bright-field stain, Giemsa. Stains were applied to dried blood smears on glass slides, with blood taken from fingerling fish without sacrificing the fish. Both stains produced comparable quality visual comparisons, with significant differences ( P < 0.001) between nuclear dimensions of 2N and 3N cells. Triploid nuclei were larger and more elongate than diploid nuclei. Karyotypic comparisons revealed that diploid fish had 54 chromosomes, while triploid fish had 81. Ethidium bromide nuclear staining required only 3 min after slides were air-dried and fixed, while Giemsa staining required more than 50 min.