194 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



case of many species are very transparent, are protected by this trans- 

 parency, which renders them to a great extent invisible in water. The 

 transparency of the larval shad is notorious, and with the exception of 

 the glittering iris and two dark lines of pigment cells above and below 

 the intestine, would be almost invisible in the water; yet it is evident 

 from our experience that this transparency affords little or no prtection 

 from so sharp-sighted an enemy as the stickleback. And if it could be 

 shown that one stickleback under natural conditions could devour a 

 dozen shad larvae in an hour in the weedy flats of rivers, where the natu- 

 rally spawned young of Alosa may be supposed to abound, the destruc- 

 tion of such larvae during a season must be enormous in respect of num- 

 bers. The foregoing observations tend to show, it would appear to the 

 writer, that the transparency of larval fishes is practically of no avail 

 in the presence of the predaceous species of their own class. If shad 

 larvae are visible to sticklebacks, there is no valid reason why they should 

 not be equally so to young predaceous fishes of a dozen other species, 

 and if, as we may suppose with good reason, not unsupported by obser- 

 vation, that young fishes will be attracted to weedy flats on account of 

 the insect prey which there abounds, we may be almost equally certain 

 that any very young fish larvae, although still transparent, will not es- 

 cape the vigilant eyes of their finny enemies, and consequent destruc- 

 tion. 



The larvae of many neuropterous insects which undergo their trans- 

 formations in water, as well as those of certain coleoptera, such as Dytis- 

 cus, are noted for their predaceous habits. I have seen the larvae of the 

 dragon-fly capture and devour a young salamander almost or quite as 

 large as itself. These gourmands of both the neuropterous and coleopter- 

 ous order are probably not excelled in rapacity by any small fishes, though 

 their rapidity of movement is probably not as great as that of the latter. 

 Now as to the facts of the case, I find upon trial that both neuropterous 

 and coleopterous larvae are capable of destroying young shad, but to what 

 extent I am not assured, as a sufficient number of observations are 

 wanting. 



The main point at which we have been aiming is, however, clear. 

 Transparency is no safeguard from either active vertebrate or inverte- 

 brate enemies, and now the question arises as to the point already urged 

 in a former paper by the writer, as to the expediency of setting shad 

 larvae free in weedy shallows in rivers where it is found that their nat- 

 ural food abounds, together with their enemies. The only answer that 

 seems possible under the conditions as we now know them is the fol- 

 lowing : That it is best to put the larvae where they will soonest find food, 

 although they be at the same time brought iuto the presence of the greatest 

 number of enemies. The chances of survival seem to me to be greater 

 where the food is most abundant, for the following reason : Notwithstand- 

 ing the fact that many enemies may be present, the chances to obtain 

 food in such places are so much more favorable, so that the growth and 



