鳙、鲢杂交种的形态学研究

鳙、鲢是我国主要的淡水养殖鱼类,有关它们的鳃耙(方秉文)、鳞片、咽骨、咽齿(朱元鼎;王应天等)和消化道(倪达书和蒋燮治;林浩然)结构的研究,过去曾有一些报道,孟庆闻和苏锦祥对白鲢作了系统的解剖。1958年秋季,我们在杭州上城河利用鳙(Aristichthys nobils)×鲢(Hypophthalmichthys molitrix)得到鳙、鲢杂交种,杂交子裔大多生长发育良好。为了对鳙、鲢杂交种作进一步的了解,近年来,我们就杂交种和鳙、鲢纯种的外部形态、骨骼、消化道及鳔等进行形态学的比较研究。杂交种在部分养殖场已经试行生产,因此先作这样的基础研究,为进一步开展对这一新品种的研究是有

MORPHOLOGICAL STUDIES OF THE HYBRIDS OF ARISTICHTHYS NOBILIS AND HYPOPHTHALMICHTHYS MOLITRIX

Tens of thousands of hybrids of A. nobilis and H. molitrix wereobtained by artificial fertilization in the autumn of 1958, and most of themdeveloped normally. A series of studies of external morphology, skeletal system,alimentary tract, air-bladder, etc. of the hybrids (30-70 cm. in length) havebeen made in comparison with the specimens of their parental strains of thesimilar length and age. The results are summarized as follows: 1. The hybrids are silver gray in color provided with dark flecks overboth sides of the trunk. The ratio of the length of the head to the lehgth ofbody is about 1:4. The length of snout, the width of mouth, the distance be-tween two eyes, the size of the black and yellow chromatophores, etc. are allof the intermediate types of the parents. The tip of the pectoral fin overlapsthe basal portion of the abdominal fin and the anterior end of the abdominalkeel lies between the pectoral and the abdominal fins (Figs. 1-6). 2. As in the case of A. nobilis and H. molitrix, the secondary sexual cha-racter of the hybrid (the serrature on the pectoral fins of the male fish) makesits appearance before the maturation of the gonads and will then last thro-ughout the life. However, the serrature in the hybrids is found finer in size andcloser in arrangement than that in H. molitrix (Text fig. 1). 3. The scales are all of the cycloid type. The number of radial canals ofthe scale is always less than that of A. nobilis and more than that of H. moli-trix (Figs. 7-9). There are 96-106 scales along the lateral line. 4. The skeleton of the hybrid is smaller and compacter than A. nobilis,but larger and looser than H. molitrix (Figs. 10-15, 16-24). Some importantdifferences among the skeletal system of the hybrids and their parents arelisted in the table. 5. The size of the plait of the mucous membrane (Figs. 25-27) and thelength of the gill-raker plate (Figs. 28-30) of the hybrids are all of the inter-mediate types. The number of rakers on a plate and the number of theprocesses found on a single raker of the hybrid are approximately equal to thoseof A. nobilis, but attain about half of those of H. molitrix. The number of gill-filaments in an arch is observed to be similar to that found in H. molitrix (butgreater than that in A. nobilis). The rakers of H. molitrix form a thick sifting apparatus and always connect with each other to make a net-like structure; onthe contray, those of A. nobilis are not provided with sifting apparatus andalways separated from one another. Nevertheless, in the hybrid, the terminalportion of most of the rakers is separated and the basal 4/5 of them is providedwith processes to form an incomplete sifting device (Figs. 28a, 29a, 30a). 6. The hybrids live on planktons, especially minute animals. The averagelength of thier alimentary tract is 5 times thier body length. It is quite similarto that of A. nobilis, but shorter than that of H. molitrix. 7. The air-bladder is subdivided into two chambers. The anterior chamberis shorter and wider than that of H. molitrix, but slenderer than that of A. no-bilis. The posterior chamber, which is always small, is sometimes of the pater-nal form, sometimes of the maternal form and still sometimes of various tran-sitional forms (Text fig. 2). It is evident that the hybrids thus obtained are true hybrids of the inter-mediate form. The anatomical structure of the gill-rakers, the pharyngealbone, the pharyngeal teeth and tho alimentary tract of the hybrids not onlyreflect the intimate correlation between function and organization, but alsoshow the closc relationship in inheritance.