ON THE BIOLOGY AND CULTURE OF THE MUD CARP,CIRRHINUS MOLITORELLA

The feeding habit,age and growth,and the propagation of the mud carp,Cirrhinus molitorella,has been studied.And suggestions concerning its culture have beenmade accordingly.The mud carp feeds mainly on phytoplankton.When water temperature is bet-ween 16.4℃ and 29.4℃,the fish have a strong appetite,above and below this tem-perature feeding declines.Most fish cease to eat at a dissoved oxygen level of 0.24—0.65 mg/l,and when the oxygen level exceeds 0.99 mg/l the feeding of the mudcarp becomes quite active.The age of the fish was determined according to the disposition of the circuli ofthe scales.New circuli are formed between March and November,which denote thegrowing period of the fish.Among the fish examined,the largest female had a body-length of 595 mm,wei-ghing 4,100 g,10 years of age;the largest male's body-length was 580 mm,weighing3,850 g,9 years of age.The correlation between body-length and body-weight is calculated for 261 fishfrom Yu-kiang River and for 382 pond-reared fish.Pearl-organs appear on the head and pectoral fins of the mature male duringApril through July.The females have none.The sex ratio of the 1,119 fish examined was about 1∶1.But when the fish weredivided into different size-groups,it was found that the proportion of the maledecreased as the size increased.The seasonal changes of the ovaries and the testes of the pond-reared mud carpwere studied.And the gonadal development of the pond-reared mud carp was com-pared with that of the mud carp caught from Yu-kiang River.It is found that the mud carp is capable of natural spawning in the Da-wang-tan Reservoir.During the years of 1962—1964,the spawning grounds of the mud carp inYu-kiang River were investigated.The ecological conditions for spawning include:water level rises rapidly （0.37—2.12m within 24 hours）,the velocity of currentincreases markedly,and the water temperature ranges between 25.9 and 29.6℃.The minimum size for sexually mature individuals are as follows:fish from Yu-kiang River,female 273 mm,525 g,male 275 mm,415 g;pond reared fish,female247 mm,366 g,male 235 mm,291g.According to the data obtained from 28 fish,the fecundity for river fish is 84 eggs/g body-weight,and 139 eggs/g body-weight for pond reared fish.The embryonic development is divided into 4 stages and 26 periods while thepost-embryonic development,8 stages.Induced spawning has been successfully carried out from early-May until mid-June,with the water temperature from 22℃ to 29℃.Spawning takes place 4.5 to6 hours after the injection of pituitaries or gonadotropins.According to the experiences of the fish-farmers,in ponds for poly-culture ofvarious fish,a stocking rate of 1,000 fingerlings of the mud carp to each mou（666m2） is suitable,the number of the silver carp （Hypophthalmichthys molitrix）fingerlings stocked should be kept at one-third that of the mud carp.In pondswhere the mud carp is intended to be the main object,a rate of 1,500—2,000 permou is desirable.