Ecology Study And Breeding Biology Research Within Different Environmental Sanity Of Medaka (Oryzias Latipes)

We researched medaka(Oryzias latipes) which habited in a marsh of Qin-huangdao,Hebei,China last four years.We surveyed ecological environment and got some environmental characters of medaka (Oryzias latipes) lived in the marsh. At the same time, We also researched a part of breeding biology of medaka within diverse sanity, which mainly include the brood survival rate; performance of sexual behavior; fertilization rate of egg; rate of hatchability of fertilized egg; deformity rate of fry; meanwhile We also measured the diameter of fertilized egg and the overall length of fry. By studying the part of breeding biology of medaka within different environmental sanity, we can get the proper range of sanity for medaka to breed. We hope to provide some theory's support for medaka protection of our country. We founded by studying the ecology of medaka habited in a mash of Qinhuangdao that sewage release from a village increased nutrient levels in open water areas of the marsh, while in cattail (Typha angustifolia) and reed (Phragmites communis) beds the nutrient levels were decreased. Zooplanktons were fewer in the cattail and reed beds compared with that in open water areas. Sampling of fishes with trap nets showed that medaka (Oryzias latipes) lived in dense populations in the cattail and reed beds, while the other three fish species, wild goldfish (Carassius auratus), topmouth gudgeon (Pseudorasbora parva), and mud loach (Misgurnus bipartitus), occuppied the open water areas in the marsh. A little amount of paradise fish (Macropodus chinensis) was also found in the marsh. Japanese freshwater shrimps (Macrobrachium nipponense) were found only in the influx canal from waterworks. Indoor aquarium experiments showed that wild medaka in this marsh was easily cultured with commercial feed similar to domesticated strain.The author use the medaka captured in the marsh of Qinhuangdao as experimental material to study its part of breeding biology within different sanity included freshwater(0‰),5‰,15‰,20‰,seawater. Results indicate that medaka can survive normally in all sanity. Brood death rate was 8% during experiment and without significant difference among all sanity group. Moreover, most of brood dead because of injure of net in the time of temporary foster. Sexual behavior of brood within 5‰sanity group was first came up. The performance of sexual behavior become more and more obvious with sanity increased. However, the performance sexual behavior of brood in seawater with 30‰is not more obvious than other groups. During experiment,the number of egg spawned of 15‰group is maximum and others is 5‰,20‰,seawater (30‰),freshwater(0‰) group respectively. The number of egg spawned of freshwater group is minimum. The fertilization rate of egg of 5‰group is maximal with 76.34% and others is freshwater(0‰),15‰,20‰,seawater (30‰) group with 60.91%,51.97%,41.06%及17.45‰respectively。The diameter of fertilized egg among all groups has not significant difference (P>0.05). The average diameter of fertilized egg all groups is 1.0124mm(freshwater 0‰),0.9932mm(seawater 30‰),0.9904mm(20‰),0.9742mm(15‰),0.9712mm(5‰) respectively from maximum to minimum. In the aspect of hatching rate, 5‰sanity group is highest about 73.80% and others are 15‰,freshwater and 20‰groups with 70.78%,42.50%及17.19%respectively. However, there are only two fry hatched in seawater group and hatching rate is only 0.67%. Most embryos happen to die gradually when they develop to the stage of heart beat and obvious blood cycle. In the aspect of deformity rate of fry,20‰group is highest about 5.51% and others are 15‰and 5‰groups with 0.80%和0.60% apart from seawater group. Apart from seawater group, the overall length of fry of 5‰and 15‰groups has not significant difference with the other two groups. The overall length of fry is 3.1888mm(freshwater),3.1184mm(20‰),2.9184mm(15‰),2.8952mm(5‰) respectively from maximum to minimum. Include all the results, we can say that it is helpful for medaka to breed to improve the sanity at some tense, when other case are the same. We can get that 5-15‰is the ideal sanity range for medaka to breed by this experiment.