Li Si-Fa, Zhao Yan, Fan Wu-Jiang, Cai Wan-Qi, Xu Ying-Fang
Key Laboratory of Aquatic Genetic Resources and Utilization Certificated by the Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, China.
Dongwuxue Yanjiu. 2011 Oct;32(5):521-7. doi: 10.3724/SP.J.1141.2011.05521.
Successful crossbreeding between Oreochromis niloticus and Sarotherodon melanotheron to produce a commercial hybrid has been difficult. The karyotypes and isoenzyme of these two species and their reciprocal hybrids (O. niloticus female × S. melanotheron male, S. melanotheron female × O. niloticus male, the last not included in the isoenzyme study) were investigated via metaphase chromosomes obtained from head kidney cells and electropherogram of lactate dehydrogenase (LDH) isoenzymes from the liver, kidney, white muscle, heart, and eye balls. The diploid chromosome number (2n=44) and the fundamental number (NF=50) of the four tilapia genotypes were the same. However, the karyotype of O. niloticus had three pairs of sub-metacentric (sm), twelve pairs of sub-telocentric (st), and seven pairs of telocentric (t) chromosomes, while S. melanotheron had one pair of metacentric (m), two pairs of sm, 12 pairs of st, and seven pairs of t chromosomes. The reciprocal hybrids both showed a mixed karyotype range between their parents: 0.5 pair of m, 2.5 pairs of sm, 12 pairs of st, and seven pairs of t chromosomes. In view of the electropherogram of isozymes, only the LDH of the kidney showed significant clear bands, with five bands in O. niloticus, three bands in S. melanotheron, and duplicated six bands in the hybrids. The bands varied depending on their activities and mobilities. We considered that the differences in karyotype and isoenzyme were related to the genetic mechanism for post-mating isolation, and provided some additional basic genetic background of their taxonomy.
尼罗罗非鱼（Oreochromis niloticus）和黑背罗非鱼（Sarotherodon melanotheron）成功杂交培育出具有商业价值的杂交品种一直颇具难度。通过对头肾细胞中期染色体以及肝脏、肾脏、白肌、心脏和眼球中乳酸脱氢酶（LDH）同工酶的电泳图谱进行研究，分析了这两个物种及其正反交杂种（尼罗罗非鱼♀×黑背罗非鱼♂，黑背罗非鱼♀×尼罗罗非鱼♂，后者未纳入同工酶研究）的核型和同工酶。这四种罗非鱼基因型的二倍体染色体数（2n = 44）和臂数（NF = 50）相同。然而，尼罗罗非鱼的核型有三对亚中着丝粒染色体（sm）、十二对亚端着丝粒染色体（st）和七对端着丝粒染色体（t），而黑背罗非鱼有一对中着丝粒染色体（m）、两对亚中着丝粒染色体（sm）、十二对亚端着丝粒染色体（st）和七对端着丝粒染色体（t）。正反交杂种均呈现出介于双亲之间的混合核型范围：0.5对中着丝粒染色体（m）、2.5对亚中着丝粒染色体（sm）、十二对亚端着丝粒染色体（st）和七对端着丝粒染色体（t）。就同工酶电泳图谱而言，只有肾脏中的LDH呈现出明显清晰的条带，尼罗罗非鱼中有五条带，黑背罗非鱼中有三条带，杂种中有六条重复带。这些条带因其活性和迁移率而有所不同。我们认为核型和同工酶的差异与交配后隔离的遗传机制有关，并为它们的分类学提供了一些额外的基础遗传背景。
