Comparative analysis of intermuscular bones in fish of different ploidies

We documented the number, morphology, and distribution of intermuscular bones in five fishes of different ploidy： Carassius auratus （Abbr.WCC, 2n=100）, Carassius auratus variety PengZe （Abbr.PZCC, 3n=150）, improved triploid crucian carp （Abbr.ITCC, 3n=150）, improved red crucian carp （Carassius auratus red var., Abbr.IRCC, , 2n=100）, and improved allotet- raploids （Abbr.GAT, （, 4n=200）. The number of intermuscular bones in WCC, PZCC, and GxAT ranged from 78 to 83 （n =81）, 80 to 86 （n =84）, and 77 to 84 （n=82）, respectively. The numbers in ITCC and IRCC were significantly lower, ranging from 77 to 82 （ n =79） and 58 to 77 （ n =71）, respectively. The average number of intermuscular bones in each sarco- mere, ranked in order from highest to lowest, was 0.721 （WCC）, 0.673 （PZCC）, 0.653 （GAT）, 0.633 （ITCC）, and 0.608 （IRCC）. There was no difference between ITCC and GxAT or between GxAT and PZCC. However, the average number of intermuscular bones in the sarcomeres of ITCC, WCC, and PZCC differed significantly, as did that of IRCC and the four other kinds of fish. The intermuscular bone of these five fishes was divided into seven shape categories, non-forked （I）, one-end-unequal-bi-fork （）, one-end-equal-bi-fork （Y）, one-end-multi-fork, two-end-bi-fork, two-end-multi-fork, and tree- branch types. Generally, the morphological complexity was higher in the anterior intermuscular bones than in the posterior body. The number of intermuscular bones was similar but not equal between the left and right sides of the body. ITCC had sig- nificantly fewer intermuscular bones than either WCC or PZCC, making it of greater commercial value. Additionally, IRCC and ITCC had fewer intermuscular bones than WCC. Our observations are significant in both fish bone developmental biology and genetic breeding.