饲料中添加食盐对低盐养殖凡纳滨对虾肌肉组织形态结构的影响

以凡纳滨对虾Litopenaeus vannamei为研究对象,在基础饲料中分别添加0（对照组）、1%,2%和4%的食盐,配制成4种实验饲料,在低盐养殖水体中饲养40d后,采用光镜、电镜等技术对4种低盐养殖凡纳滨对虾第2腹屈肌组织形态学进行观察和对比,并与海水虾做比较,探讨饲料中添加食盐对低盐养殖凡纳滨对虾组织形态结构的影响。结果表明,光镜下,对照组及添加食盐1%组肌束内肌纤维排列疏松,有聚集成束状,肌束间隙（肌束膜）较宽,纤维有弯曲状存在。添加食盐2%组、4%组肌纤维排列依次紧密,分布较均匀,与海水虾差别不大;电镜观察对虾腹屈肌横切面图片发现,对照组和添加食盐1%组的粗丝与细丝分布较稀疏,排列不规则,部分区域肌丝残缺。添加食盐2%组的肌丝分布相对较均匀,但细肌丝小且数量多,不规则的排列有时成簇状。添加食盐4%组和海水虾差别不大,肌丝分布较规则,可看到粗细肌丝呈六角形点阵排列。纵切面上,添加食盐1%组与2%组肌节排列不整齐,有弯曲交错现象,4%食盐组形状规则,肌节明显,清晰可辨,肌节长度显著高于对照组、1%和2%食盐组（P〈0.05）。饲料中添加食盐对低盐养殖凡纳滨对虾肌原纤维直径、实心粗肌丝直径、空心粗肌丝直径、暗带长度和H带长度之间无显著性影响（P〉0.05）。

Effects of dietary salt level on muscle histology and morphology of the shrimp Litopenaeus vannamei reared in low salinity water

Litopenaeus vannamei was fed with basal diets respectively supplemented with 0%, 1%, 2% and 4% salt and cultured in low salinity water for 40 d. The study was conducted to investigate the histology and morphology of the shrimp reared in low salinity using light microscope and electron microscope, and also compared with the seawater shrimp. Light microscope observation showed porosity of muscle fibre in shrimps of the control and 1 % treatment group, some were gathered cord, some were bent, and the gap were wide between some perimysium. But as the addition of salt increased, muscle fiber characteristics were improved, especially for the 2 % and 4 % treatments. Muscle fibres of shrimps in these treatments were better distributed than the other group. The ultrastructure of the shrimp under electron microscope showed irregular array of the myofilament, and incomplete in the control and 1% treatment. The distribution of myofilament in 2 % treatment was relatively homogeneous, but the thin filaments had small diameter and large quantity. Some irregular filaments were arranged in clumps. But the 4% treatment was much better, and not different from seawater shrimp; the filaments all distributed uniformly and in the form of hexagonal lattice array. On longitudinal section, the sarcomere in the 1% and 2% treatments were untidy, some were twisted and overlapping; while those in the 4% treatment were well-shaped, clearly-distinguishable, and the length of sarcomere were significantly greater than the other treatments （P〈0.05）. As the addition of dietary salt increased, myofibril diameter, solid thick filament diameter, hollow thick filament diameter, and A and H band width showed no significant difference（P〉0.05）.