| The amphipod Eogammarus sinensis belongs to the gammaridean crustaceanswhich is widely distributed along the coastal and estuarine ecosystems of the YellowSea and Bohai Sea in northern China. Because of its easy maintenance and the fact thatthe yield of offspring is abundant, this amphipod is a favourable choice for the diet oflarge decapod crustaceans in China, such as the shrimp Penaeus chinensis. In thecurrent study, we investigated its basic features of developmental biology and ecology.The embryonic development processes and life history were recorded usingexperimental ecology combined with basic biology methods. The influence ofenvironment factors on the growth and development were determined. Then, thepossible reason which might lead to the difference of growth was estimated. At last, thestudy was designed and Corophium sp. and E. sinensis were transplanted into farmpond-reared prawns P. chinensis. Our results will be useful in the mass production ofthis species for use in aquaculture. Details on the studies of this paper were as follows:1. The preliminary study on the life history of E. sinensisObservation described the life history including life cycle and breeding cycle wasstudied using the combination of morphological, physiological and ecological methods.It will be useful to learn about the biological characteristics of E. sinensis such asreproduction and growth. The longest survival time of f1generation female of E.sinensis recorded was179days, the male was260days under the conditions of20℃and a13h light/11h dark cycle. The number of eggs showed positive correlation to thelength of female E. sinensis and the relation can be described by equation y=7.4696x-42.257, R~2=0.8147. The sex ratio of f2infants were determined to be about1.55：1（♀：♂）The sexual maturity period of juveniles released was35to40days. Matured femaleand male of E. sinensis mated one time every2to3weeks. Within a certain period of time, larval quantity production increased with the increase of the body length of female.Female spawned about8to11times in her life.2. The embryonic development of E. sinensis and its relationship with watertemperatureThe embryonic development process was studied and the relationship between theembryonic development and the main environmental factor temperature. The resultindicated that the development process of E. sinensis embryo was about220hoursunder the conditions of21℃, salinity28~33and pH7.74~8.03. The hatched larvaewas with similar morphological characters to those of adult. Temperature showedsignificant influence to the embryonic development time (P <0.01). Within15~27℃,the embryonic development time decreased with the increase of temperature, and viceversa. The maximal and the minimal development rate were0.15d-1and0.07d-1.Hatchability was significantly influenced by temperature (P <0.01) and presented aupside-down parabolic curve with the increase of temperature. Based on thedevelopmental time under the different temperature, the developmental thresholdtemperature (C) was calculated to be6.02℃, sum of effective temperature (K) was137.30d·℃and the formula of duration calculation was N=K SK137.307.90/T （C Sc）=T (6.020.89).3. Effects of temperature and salinity on survival and growth of E. sinensisIn the current study, the effects of temperature (15,20,25,30℃), salinity (5,10,15,20,25,30and35) and temperature-salinity combination (five temperatures15,18,21,24and27℃and four salinities15,20,25and30) on the development, fecundity,survival and growth rate of E. sinensis were investigated.1) The results showed that thattemperature had significant effects on the development of E. sinensis (P <0.05), butthat different salinities did not (P>0.05). As the temperature increased, the duration ofembryonic development of E. sinensis decreased. Fecundity was affected significantlyby temperature and the combination of temperature and salinity, but not by salinityalone. The number of juveniles released from each female E. sinensis was significantly influenced by the temperature and the salinity-temperature (P <0.05), but not in thesalinity treatment group. Within the temperature limits of15and30℃, the relation canbe described by equation y=–0.1958x2+7.2975x–36.037, R2=0.9952. Survival ofmatured E. sinensis was affected significantly by the temperature but not the same casein the new born organisms. There was positive correlation between the length and theweight of E. sinensis which could be described as the equation that: BW=5E–05BL2.4999, R2=0.9665. In addition, high temperature accelerated the growth rate of E.sinensis juveniles within15℃to25℃, and the largest daily growth rate and specificgrowth rate were recorded as0.23mm/d and6.40%/d respectively at25℃. Higher thanthat, growth of E. sinensis was inhibited. Whereas, high salinity reduced the growth of E.sinensis and the maximal body length and body weight were detected at salinity30and20. Between the salinity5~35, the body length and body weight showed no obviousdifference.2) The results of temperature-salinity combination showed that thattemperature had significant effects on the development of E. sinensis, but that differentsalinities did not. As the temperature increased, the duration of embryonic developmentof E. sinensis decreased. Fecundity was affected significantly by temperature and thecombination of temperature and salinity, but not by salinity alone. In addition, hightemperature accelerated the growth rate of E. sinensis juveniles, whereas high salinityreduced it. Therefore, our data suggest that the E. sinensis tolerates a wide range ofsaline conditions and that temperature has more significant effects on the embryonicdevelopment, fecundity and growth of E. sinensis than does salinity.4. Effects of temperature on feeding rate and digestive enzyme activity of E. sinensisDifferent temperatures on the feeding rate and digestive enzyme activity of E.sinensis were determined and analyzed by using physiological ecology methods. Theactivities of pepsin, trypsin and amylase in E. sinensis presented an increasing trendwithin the temperature scope of15to25℃. Pepsin, tryptase and amylase activity ishigher between20to25℃, which shows that the scope of temperature is the optimumtemperature. And there were significant differences on digestive enzyme activitybetween temperature treamtment groups (P <0.01). As the index to evaluate the feeding habits of crustacean, amylase/trypsin (A/T) value fluctuation is small, and the A/Tvalues are between1.2to1.5. It seems that the larvae of E. sinensis is partial to plantdiets. Consumption rate of E. sinensis juveniles was affected greatly by the temperature,and the maximal consumption rate was calculated to be89.84%according to thecorrelation equation (y=-0.7544x~2+33.297x-277.57, R~2=0.9577) within20℃to25℃. Moreover, the assimilation rates were similar between the juveniles and the adultsof E. sinensis. The maximal assimilation efficiency was59.86%and56.86%and theoptimal temperatures were21.30℃and21.24℃.5. The small ecological breeding test for shrimp farming by feeding biological baitgammarid amphipodsA small ecological breeding test for shrimp farming by feeding biological bait wasdesigned. The polyculture experiment was composed of Corophium sp., E. sinensis andP. chinensis in the cylindrical tank. The results showed that the initial density of P.chinensis might be the main limiting factor to control the total output of P. chinensis.High density may bring a good total yield but with the small individuals, while lowdensity bring large individuals but with low total yield of P. chinensis. Based on theoverall consideration of growth and total yield of P. chinensis, we proposed thecombination of Corophium sp., E. sinensis and P. chinensis that of each species wasrespectively as follows:10g-40g-35individuals. Meanwhile, it seems that the biomassof living bait is an important factor to influence the yield of P. chinensis, but the detailedcorrelation need to be researched further. The proposed consists of living baits and P.chinensis was set up on the basis of pilot scale test, which would be amended in thefollowing cultivation in large scale. |
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