摘要
鰔鱼(Elopichthys bambusa)在我国南北各地分布很广，江汉平原的水系中产得尤其多。它是一种所谓凶猛鱼类，早在14毫米长的鱼苗时期就巳能捕食其他鱼苗。又因为它生长快、体形大——可达50公斤以上——而且行动迅速善于猎食，所以鰔鱼是我国养鱼业上著名的“害鱼”，也一向是清除的对象。
1.The intestinal contents of 969 samples of Elopichthys bambusa were examined during the complete year from February 1955 to January 1956,all from Liang-Tze Lake in Hu-peh Province.Every fish yielding even only small fragments of bones,scales,spines or rays,were considered to be“with food”or“feeding”.The various species of food- fishes were identified by their characteristic pharyngeals,cleithra,and other bones found in the intestine of the predator.From these bones the original length,height,and weight, of the food-fishes have been reconstructed. 2.The percentage of Elopichthys“with food”averages for the whole year,31.2% (feeding percentage).Regarding this as an index,the feeding intensity of E.bambusa is not very remarkable. 3.Elopichthys feeds exclusively on fishes:19 species have been discovered to be victims.Erythroculter mongolicus is the most important of them.It occupies first place both in total frequency and in rate of incidence,accounting for 23.8% of the total number of food-fishes,while the rate of incidence is 29.0%.The second in numerical abundance is Gobio argentatus,accounting for 16.7%;Erythroculter ilishaeformis comes third,with only 9.7% of the total number.According to the rate of incidence,the second in im- portance is E.ilishaeformis(12.5%),and the third place is held by Acanthobrama simoni (10.9%). 4.Elopichthys feeds sparingly,or almost ceases to feed,in the cold weather of winter and early spring.While the transition to normal,from an extremely low feeding- intensity,occurs rather abruptly,that from normal intensity to nearcessation occurs gra- dually.The fish take food normally(at a normal rate)at lower temperatures before the declining phase than they are ever known to do during the transition phase up to normal intensity,and at still lower temperatures only does the feeding begin to decline. 5.The feeding intensity as expressed by feeding percentage seems to be lower in larger predators than in smaller.The feeding percentage of fish less than 79.9 cm.long is 32.1%,and that of fish over 80 cm.long is 17.4% 6.It seems that there is a tendency for Elopichthys to prefer fishes of more slender form as food.But at the same time it is evident that behavionr,such as mode of swim- ming,location of habitat,etc.exerts the predominant influence on food selection.Hemi- culter leucisculus has a body height similar to that of E.mongolicus(height in length respectively 17.3% and 17.1%),yet owing to its swimming movement,and its darting forwards in a zigzag way when disturbed,it often eludes capture and its significance in the food list is not high.These aspects of food-selectivity by Elopichthys are possibly governed by the structure of its seizing organ,its mouth.There is a knob at the anterior end of the upper iaw and a corresponding notch on the lower jaw,These appear to be the only adaptive structures to its predatory habit.The mouth is not armed with parti- cularly effective seizing and holding structures,such as the powerful maxillary teeth of Some non-cyprinid fishes,like Esox,for example.Also,the gape of its mouth is not very large.Thus,Elopichthys is a not very effective predator:it cannot catch large or swiftly swimming fishes for food.The quantity of any given species of food fish in the lake, that is,its aceessability to the predator,is an important external factor in its being selected. 7.The four economic cyprinids,Mylophatryngodon,Ctenopharyngodon,Hypophthal- michthys and Aristichthys,Which are the chief species in Chinese pond culture,were not found as food in the intestine of Elopichthys in the lake.Therefore,it would seem that in this lake,Eloplchthys can do little harm to the so-called culture-fishes.It is very likely that the same situation is repeated in other natural lakes,and in ponds,particularly where other fishes of slender form are in abundance.
