| American shad, Alosa sapidissima belonged to Clupeomorpha, Clupeiformes, Clupeidae and Alosa. As the same Alosinae species of the Alosa sapidissima and Tenualosa reevesii, they are similar in morphological characteristics and life habit. Both of them are anadromous species with very high nutritional value and economic value. So the American shad can be cultured, popularized and as a substitute for Tenualosa reevesi which is in an endangered situation. With the increase rate of hatchability, seeding cultivation and cultivating survival, the development of aquaculture of American shad will have remarkable economical and social benefits. So the aim to discuss the development pattern of American shad and lead a healthy breed aquatics, in this paper, morphology and histology were analyzed the embryonic development, the growth characteristics and the development of digestive system in larval and juvenile American shad, at the same time, the morphological characteristics and karyotypes were studied.Forty-seven samples of Alosa sapidissima were dissected and observed. The fish has a moderately fusiform body, Silvery in color with blue or blue-green metallic luster on back. Lower jaw not rising steeply within mouth, well developed adipose eyelid, large cycloid scales, lateral line poorly developed with 56～62 scales. Gill raker is long and slender with 24～31+47～55 gill rakes on the first arch. Fin soft rays: dorsal-1, rays 3―13～16; ventral, rays 1―8; pectorals, rays 1―16～17; anal-1, rays 1～2―17～19; caudal, distinctly forked, rays 23. The measurable parameters ratios of morphological characteristics for Alosa sapidissima also were described. The Y-shaped stomach is well developed with 92～115 slender pyloric caeca. The swim bladder consists of one anterior chamber and one posterior chamber. The relationship between body length (L) and body weight (W) was expressed as W=0.0096L3.142 (n=47, R2=0.9753) and the coefficient of fatness is 1.53. The number of diploid chromosome is 2n=48 and the karyotype is 4sm+44t, NF=52, no strange size chromosomes relation to sex was observed.The fertilizing eggs of American shad were introduced from West coast of American in 2008 and the observation of morphological development of larva and juvenile of American shad were carried on. Under water temperature 20.3～21.9℃, the duration of hatching lasted 82h, according to the morphological characteristics, the embryonic development of Alosa sapidissima may be divided into 7stages: the fertilized egg stage, the cleavage stage, the blastula stage, the gastrula stage, the neural stage, the organogenesis stage and the hatching stage. The fertilizing egg of Alosa sapidissima was spherical, semibuoyant and no oil globule with diameter of 2.85 mm-3.28 mm. The total length of the newly hatched larva was 8.56±0.36 mm and the volume of the yolk sac was 4.57±0.77mm3 by using the formula of V=4/3π·R/2·(r/2)2. The mouth and anus opened during 1 day after hatching (DAH), meanwhile the brain began to development and the pectoral fin had formed. The volume of the yolk sac of the 2-day-old larva was 0.71±0.23mm3, just 15.54% of the newly hatched larva. Larva growth and development depend on the energy of yolk sac from newly hatched larva to 3DAH. Then larva entered a mixed feeding stage, finally the larva exhausted all the yolk sac and undertaken exogenous feeding stage in 4DAH, the relationship between the volume of the yolk sac (V) and the hour after hatching (h) was V=4.1583e-0.0356h (R2= 0.9901). Then the dorsal fin, caudal fin rays, anal fin rays and pelvic fin rays appeared in the late-stage larva and meanwhile the notochord flexion began on 9DAH. Fin ray of each fin completely developed. The scale occurred on 27DAH, the ontogeny of 33DAH juvenile went into the fingerling stages. The regression equation of the relationship between body total length (TL) and age in days (D) was TL=0.0049D2+0.5091D +9.2578 (R2=0.9885). After 33 days of rearing, the average total length of larvae was from 8.56±0.36 mm (1DAH) to 33.10±1.58 mm (33DAH). According to the structural changes in the digestive tract, larval development was divided into three stages. (1) lecitotrophic (0-2 DAH), (2) lecitoexotrophic (3DAH), (3) extrophic (4-33DAH). At hatching, the digestive system of the lecitotrophic larvae was un-differentiated with a large yolk sac. Then mouth and anus opened soon, liver was evident. During stages 2, larvae began to live an exogenous nutrition after about 1 day lecitoexotrophic, the yolk sac dissolved after 3 DAH and then the intestinal tract had a quickly development. During stages 3, the stomach was a rudiment at 8 DAH, the anterior intestine and posterior intestinal had an obviously organizational different and then the stomach shaped at 19 DAH with cardiac, fundic, pyloric region and few gastric gland. Lots of gastric gland appeared in gastric body and a certain amount of pyloric caecum formed at 25 DAH. |
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