| Procambarus clarkii is world freshwater economic shrimp, originates from south of North America. It was introduced to China in the1930s, and its distribution has expanded to Jiangsu, Hubei and Jiangxi Province. P. clarkii has become one of the most important freshwater products in China. In recent years, the value of P. clarkii is soaring and P. clarkii farming is booming throughout China. Its growing has become one of the fastest, most characteristical and potential variety of cultivation in Chinese aquaculture. But the technology of cultivation P. clarkii is poor, seeding, yields and specifications are the bottlenecks of the crayfish industry. Therefore, the reproductive biology and cultivation ecology was investigated in this article, in order to solve the limitation of the crayfish industry. The main results were present as follows:1. Warming up to stimulate Procambarus clarkii to breed in winterWarming up to stimulate Procambarus clarkii to breed in winter was researched. And the effect of temperature on hatching and larvae development of Procambarus clarkii was investigated. The results showed that the female crayfish could breed by warming up in winter. The female crayfish was oogenetic in the water tank of26℃temperature after38days. The female crayfish wasn’t oogenetic in the water tank of18℃, but the ovary developed. The eggs carried by female crayfish were fertilized and could be hatching normally. The hatching time was (39.67±3.06)d,(28.33±2.52)d and (15.00±2.00)d respectively in the tank of18℃,21℃and26℃water temperature. During45d breeding, the body length of larvae was (1.90±0.25)cm,(2.73±0.38)cm and (3.78±0.70)cm respectively in the tank of18℃,21℃and26℃water temperature, and the weight was (0.223±0.100)g,(0.688±0.331)g and (2.145±1.272)g respectively. Larvae exhibited positive allometric growth (b>3) at26℃and showed isometric growth at18℃and21℃(b=3).The hatching speed and larvae growth were positively correlated with temperature in a certain range.2. In vitro incubation of P. clarkii ovumThe effect of hatchability on different period ovum in vitro incubation and different incubation ways was researched. The results showed that the hatchability of ovum separate from crayfish after0h,72h,144h and216h were very low in standing water, no significant difference among them(P>0.05). In this way, the hatchability of ovum separate from crayfish after288h reached65.00±10.00%, was significant higher(P<0.01). The hatchability of ovum separate from crayfish after0h,72h and 144h were very low in inflating water, no significant difference among them(P>0.05). In this way, the hatchability of ovum separate from crayfish after216h reached46.67±7.64%, was significant higher(P<0.05). And the hatchability of ovum separate from crayfish after288h reached75.00±13.23%, was highest (P<0.05). The hatchability of in vitro ovum in inflating water was higher than in standing water.3. The effect of female crayfish on larval growth and survival rate.The female P. clarkii carry ovum on their abdomen. Even after the ovum hatching, the larval can be back to the crayfish’s abdomen occasionally. This experiment was conducted to study the effect of female crayfish on larval growth and survival rate. The results showed that the female crayfish was significant influence the survival rate of larval. The survival rate of larval with mother is34.00±11.14%, significantly lower than which without mother. The survival rate of period Ⅰ and period Ⅱ separated from mother were66.66±4.32%and74.00±11.14%respectively, had no significantly difference (P>0.05). After cultivation, the body length and weight of the crayfish with mother and period Ⅱ separated from mother were2.11±0.32cm,0.31±0.13g, and2.09±0.39cm,0.31±0.21g respectively, has no significant difference (P>0.05). But the body length and weight of these two groups were significant higher than the group of crayfish period Ⅰ separated from mother, which were1.67±0.27cm,0.15±0.07g respectively. The length-weight relationships for the crayfish with mother, period Ⅰ and period Ⅱ separated from mother were y=0.030x2.991, R2=0.970, y=0.029x3.030, R2=0.947and y0.028x3.083, R2=0.965respectively, all growth were isometric(b≈3).4. Length-weight and chelae length-width relationships of the crayfish Procambarus clarkii under culture conditionsLength-weight (body length; LB vs. wet weight; WWT) and chelae length-width (LCh vs. WCh) relationships were determined for male and female crayfish (Procambarus clarkii) under culture conditions. The length-weight relationships for males, females, and total individuals were described as WWT=0.014×LB3.603,WWT=0.020×LB3.350, and WWT=0.017×LB3.467, respectively. This relationship was significantly different (P<0.001) between males and females. Compared to females, males were heavier and their tail length was shorter (P<0.001). No statistical difference was observed in mean LCh, cheliped length (LCp), and WCh between the right and left sides within a gender (P>0.05), but significant differences were detected between males and females (P<0.001). The regressions for LCh vs. WCh for males and females were WCh=3.083×LCh0.847and WCh=0.284×LCh1.232, respectively. This regression differed significantly between males and females; males’ chelae were wider than those of females (P<0.001). Lch,LCp, and Wch were highly related to LB;males had longer Lch and LCp and wider Wch than females. Individuals without chelipeds were measured to determine the length and body weight(WBW) relationship. The LB-WBW relationships for males and females were described as=0.074×LB2.638and WBW=0.033×LB3.023, respectively. Females exhibited positive allometric growth (b>3), and males showed negative allometric growth (b<3). No statistical difference was observed in mean WBW between males and females when LB was used as a covariate (P>0.05).5. The growth of juvenile crayfish of different genderSexual dimorphism appears to be common in freshwater crayfish. Particularly obvious sexual dimorphism in crayfish is due largely to the disproportionately rapid growth of chelae in males compared with females. This experiment was in order to determine when the secondary sexual characteristics appeared. The results showed that the weight and length growth rate of female and male juvenile crayfish were2577.00±407.33%,171.75±10.25%and2982.40±605.97%,177.62±17.32%respectively after75d culture, has no significant difference(P>0.05). The body length and weight of male and female juvenile crayfish at different stages showed no significant difference(P>0.05). The weight of male and female has no significant difference at Od,15d,30d and45d(P>0.05), but·showed significant difference at60d and75d(P<0.05), when body length was used as a covariate. The length of female and male at60d were5.54±0.38cm and5.61±0.43cm respectively, so the secondary sexual characteristics emerged when the body length of crayfish reached around5.5cm.6. The effect of sex ratio on P. clarkii growthThe effect of sex ratio on P. clarkii growth were researched in order to understand if the male shrimps affect the growth and survival of P. clarkii. The results showed that survival rate, weight and length growth rate of female, male and two genders juvenile crayfish groups were54.17±7.22%,4996.00±1857.42%,258.33±39.83%;45.83±14.43%,4075.70±1620.98%,228.67±39.50%and37.5±12.50%,4972.70±479.65%,254.00±5.00%respectively, had no significant difference among them(P>0.05). The survival rate, weight and length growth rate of female male and two genders adult crayfish groups were91.67±8.34%,8.33±0.97%, 1.60±0.25%;83.33±8.34%,1.82±0.91%,1.41±0.20%and86.11±4.82%,24.84±2.06%,5.94±0.53%respectively. The survival rate had no significant difference(P>0.05). But the growth rate of weight had significant difference(P<0.01), two genders>female>male. The growth rate of length had no significant difference between female and male(P>0.05), but both were significant lower than the group of two genders(P<0.01). |
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