Biology Of Sepia Esculenta In The Coastal Waters Of Rizhao

The golden cuttlefish, Sepia esculenta Hoyle, 1885 (Cephalopoda: Sepioidea) is widely distributed in the Russian Far East Sea, coast of China, Japan, Korea and Philippines. It is not only one of the most important species of coastal fisheries resource in China, but also a good wild species with high commercial value. After the 1980's, due to the development of fishery and modernization, the environment of the spawning site and conservation areas for S. esculenta were threaten. The resource declined sharply in recent years because of over-fishing and natural disaster, such as typhoon that impact the eggs badly. For the purpose of protecting and making rational use of this resource, and accelerating sustainable development of the fishery, the biology and heredity of the S. esculenta population of Lan Shan Tou, Rizhao, Shandong Province, China, were investigated in this paper. In a sense, it is also important and has far extensive significance for maintenance and reproduction of the S. esculenta.The morphologic characters of configuration, cuticular ring, cuttlebone, mandible, etc. of S. esculenta were observed and described. The frequency of mantle length and body weight in different months and the growth of S. esculenta were studied through conventional measurement and statistic analysis. The relationships between some biological parameters were analyzed and the life history of S. esculenta was described. There were some differences in the results of morphology between the present study and previous reports.S. esculenta grew rapidly and the body weight and mantle length were decreased significantly in post-reproduction period. Size difference among individuals was probably caused by the difference of the time of hatching out. The relationships between body weight and mantle length, body weight and cuttlebone weight, headwidth and mantle length can be expressed with power models. The logarithm equations can describe the relationships between total length and mantle length, tentacle length and mantle length. The relationships between mantle width and mantle length, cuttlebone length and cuttlebone width, fin length and mantle length, arm length and mantle length were derived by linear regression. The relationships between body weight and mantle length, mantle length and mantle width, cuttlebone length and cuttlebone width, head width and mantle length were significantly between males and females. The relationship between body weight (TW, g) and mantle length (ML, mm) was expressed by separate regression curves as follows, TW premature =7.0 ×10-4 ML2.7207, TW=5.0×10-4ML2.7998, TW =11.0×10-4ML2.6164. The result showed that females are heavier than males of the same mantle length.The life span of S. esculenta is one year. In May and June, adults spawn and then die out. From the end of June, juveniles appear and grow fast. The average weight is 117.1 g in November and 413.4 g in March, and the weight reach maximum in May. They mate and spawn in May and June.The arm formula of S. esculenta was analyzed and its application in taxonomy was discussed. The results showed that there were many types of arm formula in S. esculenta. Duncan multiple comparisons indicated that the arm formula of them were difference in different individuals, size, left and right and sex. The Sepiella maindroni, Loligo japonica and Octopus ocellatus have the similar conditions. When all the arm formulas are same in all samples, including the left and right side of male and female, the arm formula could be the actual for the species. When arm formula of cephalopods is mentioned, there should be some propositions such as sex, left and right, size, and so on. So it is not feasible to adopt arm formula as a morphological parameter for taxonomy. It is suggested that the arm formula should be used with carefulness in the taxonomy of cephalopods.Horizontal starch gel electrophoresis was used to investigate the tissue-specificity and genetic structure of S. esculenta. A preliminary screening for 19 isozymes in six kinds of tissues (eye, branchia, mantle muscle, buccal bulb muscle, branchial heart, liver) was carried out using TC-7.0 buffer system. The results showedthe isozymes expression was highly tissue-specificity in S. esculenta. Twelve enzymes (PGDH, MPI, GPI, ME, SOD. IDHP, DIA, PGM, G3PDH, MDH, AAT and LDH) showed various degrees of activity in the six different kinds of tissues, while the others (HK, LAP, ADH, G6PD, SDH, EST and ALP) showed no reaction. Of all the tissues, buccal bulb muscle was the most suitable, most stable, and clearest for isozymes expression while liver was the worst. Eye and mantle muscle were next to buccal bulb muscle. Branchial heart was especially well suited for the reaction of Lactate dehydrogenase (LDH) and superoxide dismutase (SOD). At the same time, malic enzyme (ME) was stained only in the eye tissue, and phosphogluconate dehydrogenate (PGDH) was stained in the eye and buccal bulb muscle tissues. Twelve isozymes (PGDH, GPI, MPI, IDHP, SOD, ME, AAT, DIA, MDH, LDH, G3PDH and PGM) and three kinds of tissues (eye, buccal bulb muscle and branchial heart) were selected for genetic analysis of S. esculenta population of Rizhao coast. Among the eighteen putative enzyme-coding loci examined, three loci were polymorphic, i.e., LDH-2*, G3PDH-1* and PGM*. The proportion of polymorphic loci was 0.1667 (P0.99) and 0.0556 (P0.95). The average values of observed and expected heterozygosity were 0.0159 and 0.0143, respectively. The average effective number of alleles was 1.0201. Analysis of S. esculenta in the present study revealed low levels of genetic variability.