半滑舌鳎早期形态及发育特征

Morphological and developmental characters at the early stages of the tonguefish Cynoglossus semilaevis

半滑舌鳎卵子为分离的球形浮性卵 ,卵径 1 18-1 3 1mm。卵膜薄、光滑、透明 ,具弹性。多油球 ,一般为 97-12 5个 ,多数在 10 0个左右 ,油球径 0 0 4-0 11mm。在培养水温为 2 0 5-2 2 8℃的条件下 ,卵子授精后 3 7h仔鱼孵出 ,3 0min后仔鱼全部孵出。初孵仔鱼全长 2 56-2 68mm。 1日龄仔鱼 ,出现胸鳍芽。 1 5日龄仔鱼 ,巡游模式基本建立。 2日龄仔鱼 ,逐渐建立外源性摄食关系。 3日龄仔鱼 ,出现鳔泡 ,个体发育进入后期仔鱼期。 18日龄 ,个体发育进入稚鱼期。 2 5日龄稚鱼 ,右眼开始向上移动。 2 7日龄稚鱼 ,右眼已转到头顶。 2 9日龄稚鱼 ,右眼完全转到左侧 ,胸鳍退化 ,各鳍鳍条发育完全。 57日龄 ,个体发育进入幼鱼期。 79日龄幼鱼 ,鳔退化、鳞片发育完全 ,侧线 3条。研究结果表明 :前期仔鱼培育期间 ,除了严格控制适宜的培养水温外 ,仔鱼开口后就应及时投喂一定密度的适口饵料 ,这是苗种培育中不可忽视的重要环节和技术措施之一 ;稚鱼变态期间加强鲜活饵料的投喂是提高稚鱼变态成活率的关键所在。仔鱼孵化后出现的管状感觉器官以及背、臀鳍膜上的泡状结构在早期发育阶段的生态和生理作用尚不清楚。半滑舌鳎成鱼无鳔和无胸鳍 ,而在早期发育期间具有鳔泡和胸鳍 。

Based on the data and the samples from both the hatchery experiments carried out during 1987 to 1989 and from the large-scale seedling-rearing performed i n the Laizhou Mingbo Fish Farm in the autumn of 2002, we observed and described th e morphological and developmental characters in the early stages of the tonguefi sh Cynoglossus semilaevis Günther, 1873. In each late August during the exp erim ent years, a pair of 135 hp trawlers was used to catch adult tonguefish in the c entral and western parts of the Laizhou Bay, the Bohai Sea. Normally, those adul t fish with the gonad developing to Ⅳ stage were chosen to be the parent candid ates. As chosen, the body size of the female fish was 550-670 mm in standard len gth with a body weight ranged from 1 450 to 2 350 g while the body lengt h and weig ht of the male fish were 270-290 mm and 120-230 g, respectively. The parent fish were transported to the hatchery and cultivated in the concrete pond with a vol ume of 50 m 3. The cultivation density was 1 5-2 individuals/m 2. The femal e and m ale proportion was kept in 1∶3. The cultivation pond was shaded by black curtai n . During cultivation, the daily exchange rate of seawater was about 100% or more by supplying re-circulation water and aeration was discontinuously given to ma i ntain water quality. The parent fish were fed twice a day and rationed 3%-5% of fish body weight. The priority categories of diets were clamworm, squill and cla m meat. When the gonad of the parent fish matured after one-month culture to th e middle or late September, artificial insemination could be performed to obtain fertilized eggs. The fertilized eggs were placed in a glass tank with a volume of 120 L to incubate. On incubating, the gentle re-circulation water and fresh s eawater were supplied. The newly hatched larvae were cultured in the same glass tank by supplying gentle re-circulation of water with gentle aeration. In the second day after hatching, the larvae were fed with rotifer Brachio nus plicatilis twice a day and rationed at a food density of 5-10 individuals/ ml. The density of unicellular alga (Chaetoceros muelleri, Isochrysis galbana, Platymonas sp.) was maintained at 10×10 4 cell/ml. In the 7th day after hat ched out, the ration of rotifer was increased to 10-15 individuals/ml. In the 12 th day aft er hatched out, the larvae were supplied with both rotifers (10-15 individuals/m l) and copepod larvae (2-3 individuals/ml), while, the density of unicellular alga was maintained at or above 5×10 4 cell/ml. In the 19th day after hatchi ng, the juveniles were moved to an indoor concrete pond with a volume of 8 0 m 3 for further cultivation. Using a preheated/auto-flow device, the daily water excha n ge rate was kept at 1/2 to 2/3 of the total culture volume. The pond bottom was punctually cleaned. Aeration was supplied 4 times a day, lasting 30 minutes each time. The juveniles were fed thrice a day with the food categories of either “ rotifer + copepod larva” or “rotifer + copepod larva + Artemia nauplii” a nd “rotifer + copepod larva + Artemia nauplii + minced fish meat (particle size: 0 2-0 5 mm)”. Normally, the rations of rotifer, copepod and Artemia nauplii were maintained in the densities of 5 or 6 individuals/ml, 3-6 and 3-5 ind ividuals/ ml, respectively. But, the ration of minced fish meat was adjusted according to the feeding conditions. The cultivation temperature was kept at a range of 21 0 - 21 8℃ and the pH value at 7 90- 8 40. Dissolved oxygen was maintained at a ran ge of 3 03- 5 90 mg/ml. A luminance about 500 lux was controlled. The samples of fish eggs, larvae, postlarvae, juveniles and fingerlings were collected and pre served in 5% neutral formalin for observation and description of the morphologic al and developmental characters at the early life stages. The egg of the tonguefish was separate, spherical and buoyant with a diameter range of 1 18-1 31 mm. The chorion was thin, elastic, lubricous and transpar en t. The egg was rich in oil globules, the numbers of which were variable