AN EXCELLENT FRESH-WATER FOOD FISH,MEGALOBRAMA AMBLYCEPHALA,AND ITS PROPAGATING AND CULTURING

This herbivorous bream (Megalobrama amblycephala Yih) occurs wild in certainlarge and median-sized lakes of the mid-lower Yangtze basin and was not found elise-where.Since its recognition in 1955 as a new species distinct from Megalobramaterminalis,to which it bears a superficial resemblance,it has been subjected to generalbiological studies as well as pond-culture experimentation.Observations made in our hatcheries indicate that this bream is much more resis-tant to bacterial diseases than the well-known grass carp (Ctenopharyngodon idellus),which is highly esteemed by our pisciculturists on account of its big size,quickgrowth,tastefulness,and herbivorous food habit,yet on the other hand,it is alsonotorious for its susceptibility to bacterial infections.Except for the smaller size,this bream has as many favourable features as the grass carp and is,in other respects,even superior to the latter.Of particular interest is that this bream can matureand breed spontaneously in ordinary fish ponds.In middle Hupei,this bream spawns from late April to early June.Its eggs,like those of the common carp and goldfish,are of the adhesive type and can beincubated in the same way as for incubating goldfish eggs.But the rearing of itsfry,which are so small and delicate,is more difficult.In our experimentation forrearing the fry,better results have been obtained by letting the eggs and the newly-hatched larvae stay in the hatching pond until the fry grow to inch-sized fingerlings,in contrast to the ordinary practice (for various carps) in which the fry are to betransferred to the rearing pond shortly after they become capable of swimming abouthorizontally.At a water temperature of 26—28℃,the eggs hatch in 24—30 hours,with anaverage hatching rate of 60% both in indoor incubation and in the pond.When the yolk sac of the larvae is nearly absorbed,the fry feed first on rotifersand nauplii,but soon become large enough to feed on cladocerans and copepods.Ifthe pond is rich in zooplanktaon,the fry will grow fast with little mortality.Theproduction of natural food organisms should be promoted by manuring the hatching-rearing pond,although care should be taken not to overfertilize.Fingerlings of this bream when reared in ponds even without any prophylacticprecautions will grow nicely on vegetable diet and very rarely get bacterial infections,so they have much better chance of surviving as compared with the grass carp.Thisis also the case with the yearling cultures.Experimental polycultures with bream andgrass carp indicated that the bream had a survival of 84—89%,while the grass carp had a survival of only 14—14.5% because of bacteriai infections.Fingerling bream 10—13 cm in total length stocked in the pond at the rate of2500—3000 fish per mou will in the course of one year attain to a weight of 300 gramsper fish,which is a good size for the market,whereas fingerling grass carp usuallytakes two years to grow to its market size,thus the tempo of pond utilization can bequickened one year by raising the bream.The bream is fairly tame and easy to seine.In pond culture,the first seiningwould catch about 70% of the individuals present.In short,this bream has many favourable features to fullfil the requirements ofan excellent fresh-water food fish and is worthy of being propagated and raised.Ithas already been successfully cultured in most provinces of our country at present.