| The golden cuttlefish Sepia esculenta is a large, commercially importantcephalopod in the Far East sea of Russia and the coasts of China, Japan, Korea andthe Philippines. In recent years, the resource has sharply decreased and has been nearextinction because of excessive fishing and severe destruction of their spawningenvironment. Consequently, recovery methods and techniques have been developed torestore the cuttlefish resources. But there are still some problems, such as the lowsurvival rate of the newly hatched larvae and the high cost of the initial feeds. Tosolve these problems, it is necessary to know the physiological procsee of theembryonic and post embryonic development of this species. In this study, embryonicdevelopment and post embryonic development of S. esculenta were investigated bystatistical, physiological, histological and behavioral methods. The results are asfollows:1. A comparative study of Sepia esculenta and Sepiella maindroni on embryonicdevelopment and ability of salinity toleranceFertilized eggs of Sepia esculenta and Sepiella maindroni were collected fromthe wild and the embryonic development of S. esculenta was observed in thelaboratory. The morphological characters of fertilized eggs and newly hatched larvaebetween the two species were also compared. The effects of different seawatersalinities of20,25,30(control),33,36for S. esculenta and15,20,25,30(control),36for S. maindroni on hatching rate were studied, respectively. Changes in egg fluidosmolality and egg Na+-K+~ATPase activity of S. esculenta and S. maindroni werealso measured during the abrupt salinity changes of192h, respectively. Hatching rates of fertilized eggs at the same salinity and physiological adaptation to the abruptsalinity changes during192h were compared between S. esculenta and S. maindroni.The results showed that organ differentiation happened when embryo was7-day-old,whileorgan formation occurred when embryo was14-day-old for S. esculenta. Theincubation period of S. esculenta fertilized egg ranged from21d to22d at22~24°Cand salinity of30. Hatching rates of S. esculenta and S. maindroni under the controltreatment were significantly higher than those under the other salinity treatments(P<0.01), indicating that salinity of30is the suitable hatching salinity for fertilizedeggs of two species. Fluid osmotic pressure of S. esculenta and S. maindroni fertilizedegg changed as seawater salinity altered during the abrupt salinity change. The eggfluid osmotic pressure of S. esculenta was equal to the medium osmotic pressure,while the egg fluid osmotic pressure of S. maindroniwas60mosm/kg higher thanthose in the medium. Activities of Na+-K+~ATPase were not found in fertilized eggsof two species. These results indicate that fertilized eggs of two species have littleability in regulating the osmotic pressure. However, fertilized egg of S. maindroni canaccommodate the salinity alteration better than S. esculenta.2. Biochemical composition of cuttlefish (Sepia esculenta) eggs during embryonicdevelopmentIn this study, changes in egg volume, water content, proteins, carbohydrates,lipids, amino acids and fatty acids in cuttlefish (Sepia esculenta) were determinedduring embryogenesis to understand the nutritional requirements in the early lifephase. The egg volume and the water content decreased significantly (P<0.05) duringthe early embryonic development, and then increased abruptly after the beginning oforgan differentiation. During embryonic development, protein was found as the majorcontent in the yolk and the percent composition varied to a large extent (55.19%to78.45%). By contrast, carbohydrates (9.86%to15.56%) and lipids (1.62%to2.97%) were lower. During the embryonic development, proteins and lipids showed23.3%and0.4%decrease in dry weight, respectively, whereas carbohydrates exhibited a0.46%increase in dry weight. Total amino acids and essential amino acids (EAAs)were stable during the early embryonic developmental stage, but decreasedsignificantly until the eggs hatched (P<0.05). The largest utilisation of the yolkprotein possibly occurred with respect to EAA (25.7%) because of a decrease inmethionine (70.3%), valine (63.0%) and phenylalanine (58.5%). The most importantfatty acids were saturated fatty acid (SFA) C16:0and polyunsaturated fatty acids(PUFAs) C22:6and C20:5. Unsaturated fatty acids (UFAs) and SFA decreased at asimilar rate during embryonic development (5.69%and6.15%, respectively). ForUFAs, monounsaturated fatty acids were consumed at a greater rate than PUFAs (29.6%and0.05%, respectively). These data contribute to the understanding on thebiochemistry and physiology of cuttlefish embryos and pre-feeding larval stages.3. Effects of temperature and capsule layer on oxygen consumption andammonia excretion during embryonic development of cuttlefish Sepia esculentaThe metabolic responses of the embryo Sepia esculenta in terms of oxygenconsumption and ammonia excretion to changes in temperature and capsule layerwere investigated. Temperature had significant effects on hatching time (P<0.05). At16.0oC, the control group had the longest hatching time (49.23d), while the hatchingtime for the group with egg capsule removed was46.14d. At28.1oC, the group withegg capsule removed had the shortest hatching time (14.26d), while the hatching timefor the control group was15.61d. Temperature had significant effects on oxygenconsumption rate and ammonium excretion rate during embryonic development (P<0.05), and metabolic rate increased with the increasing temperature. The relationshipbetween temperature and oxygen consumption rate as well as ammonia excretion rateof the hatchlings could be described as the quadratic model, respectively. Metabolic rate increased with the development stage. Under all temperature conditions, groupwith egg capsule removed had higher oxygen consumption rate and ammoniumexcretion rate (P<0.05) than that in group with the capsule intact indicating that thecapsule impede the oxygen diffusion and ammonia excretion as well as prolong thehatching time of the embryo. The data contribute to optimize the hatching conditionof cuttlefish embryos.4. Study on early development and growth pattern in golden cuttlefish SepiaesculentaEarly development and allometric growth patterns of Sepia esculenta larvaeraised under culture conditions were described.From hatching to day56, ten larvaewere sampled every five day and measured dorsal mantle length, mantle breadth,body weight, cuttlebone length, cuttlebone breadth and lamella number. Therelationship between dorsal mantle length, body weight, lamella number and dayscould be described as the exponential model, respectively. However, there were twodifferent phases during early development, because of the different growth rate of thejuvenile. The lamella in the cuttlebone was notdeposited daily that demonstratedthenumber of lamellas in the cuttlebonedid not correspond to actual age.In addition,allometric growth of mantle and cuttlebone were discovered, indicating that theseimportant organs like swimming organ had developed prior to other ones.The presentresultssupport the hypothesis of differential growth patterns for primary functionsduring early ontogeny in cephalopod.5. Histological observation on sexual differentiation in golden cuttlefish SepiaesculentaIn the present study sexual differentiationwere investigated in culturedindividualsof a gonochoristic species of cuttlefish, Sepia esculenta during newly hatched larvae to107days old using light microscopy. At the time of hatching, theinitially undifferentiated gonad contains primordial germ cells. Ovarian differentiation,initiated20days post hatching (DPH), is characterized by the appearance of theoogonia. Testes remain undifferentiated until differentiation of thespermatogoniahappened at86DPH. The appearance of the developing seminiferous tubules (107DPH) confirmed testicular differentiation. The individuals that do not form an ovaryduring20DPH to84DPH are destined to become males.6. Effects of temperature fluctuations on cuttlebone formation of cuttlefish SepiaesculentaThe morphological characteristics and the cuttlebone formation of Sepiaesculenta exposed to different water temperature fluctuations were investigated underlaboratory conditions. Temperature fluctuation cycles (15cycles,60d in total)consisted of the following three regimes of4d duration: keeping water temperature in26°C for3d (Group A),2d (Group B),0d (Group C, control); then keeping watertemperature in16°C for the next1,2,4d. No significant difference in the survivalrate was observed between the control and temperature fluctuation groups (P>0.05).Lamellar depositions in a temperature fluctuation cycle were2.45±0.02for Group A,2.00±0.02for Group B, and1.78±0.02for Group C (P<0.05). The relationshipbetween age and number of lamellas in the cuttlebone of S. esculenta under eachwater temperature fluctuation could be described as the linear model and the numberof lamellas in the cuttlebone did not correspond to actual age. Group A had the highestcuttlebone growth index (CGI), the lowest locular index (LI), and inter-streakdistances comparing with those of control group. However, the number of lamellasand LI or CGI showed a quadratic relationship for each temperature fluctuation group.In addition, temperature fluctuations caused the breakage of cuttlebone dark rings,which was considered a thermal mark. The position of the breakage in the dark rings was random. This thermal mark can be used as supplementary information formarking and releasing techniques.7. Study on feeding behavior and feeding ability of juvenile cuttlefish SepiaesculentaFeeding behavior of the golden cuttlefish Sepia esculenta was observed inlaboratory conditions. The feeding behavior on prawns consisted of two phase namely,attacking and eating. The sequence of attacking behavior comprised three phases:attention, positioning and seizure. The successful feeding rate of the juvenilecuttlefish whose dorsal mantle length (DML) was>10mm was relatively high, noless than80%. The relationship between DML and feeding times, attacking distance,maximum of attacking distance, total feeding time could be described as the quadraticmodel, respectively while the relationship between DML and total feeding amount,handling time was exponential model, respectively. Feeding times, attacking distance,maximum of attacking distance, total feeding time and total feeding amount increasedwith growth while handling time decreased with growth. Feeding ability of juvenilecuttlefish rapidly increased with growth. |
