ZOOLOGICAL SOCIETY BULLETIN 



THE FRESH-WATER SHRIMP (GAMMARUS FASCIATUS) 



Its Precarious and Interesting Existence. 

 By Ida M. Mellen. 



WK have at the Aquarium in a 50-gallon 

 tank, thousands of fresh-water shrimps, 

 the descendants of a few dozen speci- 

 mens from Staten Island, collected and bred 

 from by the present writer for the feeding of 

 sea horses. Minute though these animals are, 

 no observing person can view them for two min- 

 utes without becoming interested in their be- 

 havior: and as practically nothing was known 

 regarding their development, it has seemed that 

 a special study, however limited in scope, might 

 yield some facts of value. 



Like any other animal, the fresh-water shrimp 

 is, of course, concerned chiefly with the preser- 

 vation of the individual and the continuation of 

 the species ; but aside from these common and 

 important racial obligations, it derives a con- 

 siderable amount of enjoyment from its precari- 

 ous existence. It appears to be of almost uni- 

 versal distribution, having been reported from 

 various countries, though said to be entirely 

 absent from the Malay Archipelago. We might 

 add parenthetically that this little animal is not 

 a true shrimp, but its superficial resemblance 

 is close enough to have suggested the name. 



Various guesses have been made concerning 

 the character and life habits of fresh-water 

 shrimps: — that they swim on one side; that they 

 "carry their spawn under their tails" like lob- 

 sters : that the young (like crayfishes) remain 

 attached to the mother for some time after 

 hatching: that when born they are the exact 

 counterpart of their parents : that they follow 

 their mother about like chickens after a hen ; 

 that they live in burrows; that those of maxi- 

 mum size are males, the females being smaller, 

 etc. But for strict accuracy we must refer to 

 the statement of Dr. A. E. Ortmann in Fresh 

 Water Biology to the effect that investigations 

 have been altogether lacking regarding the 

 North American forms of the group to which 

 the fresh-water shrimp belongs : the group called 

 Amphipods, — animals with bodies flattened from 

 side to side, and feet that turn some forward 

 and some backward. 



After some observations made upon specimens 

 at the Aquarium, it is possible to state that 



Xote — The illustrations are from pen drawings 

 by the author. The appendages being confusingly 

 numerous, those of only one side of the animal are 

 shown, excepting that in two of the drawings (speci- 

 men in snail's shell and those on plant) both pairs 

 of antennae are shown to illustrate the true character 

 of the head. 



they swim habitually upside down and not on 

 one side ; that the eggs are carried by the moth- 

 er, not, like lobster's eggs, attached to the 

 swimmerets. but in a brood chamber under the 

 thorax ; that the young remain in the brood 

 chamber only a few days after hatching; that 

 they are not adherent to the mother ; that they 

 never follow her about; that when born the head 

 and its appendages, including the eyes, are un- 

 like those of the parents and undergo gradual 

 changes until the adult type is reached; that 

 they do not live in burrows; and that adult 

 females are not less than maximum size, but al- 

 ways to be found among the largest specimens. 

 At birth the fresh-water shrimp measures 

 1 mm. (l/25th of an inch) in length; at ma- 

 turity 10 mm. (some say 15 mm. and it may 

 occasionally attain that length, but the largest 

 raised at the Aquarium was a single specimen 

 12 mm. long). The shrimp, which belongs to 

 the same class of crustaceans as the lobster 

 (malacostraea), is to the fish what the lobster 

 is to the human palate; and shrimps that die 

 of old age must be rare indeed. Nor is it to 

 be supposed that many die a natural death, for 

 if one falls ill, another will despatch it as here- 

 inafter described. 



In the matter of seeking comfort, the fresh- 

 water shrimp, as previously hinted, knows how 

 to make hay while the sun shines. On a bright 

 morning it may be seen near the surface of 

 the water, browsing upon the aquatic vegetation 

 and taking its ease in the branches of the plants, 

 where it assumes rabbit-like poses, cleans its 

 antennae, or repairs with a bit of food brought 

 up from the bottom. Few animals enjoy their 

 food more than the shrimp, which is omnivorous, 

 eating plant and animal substances, dead or 

 alive. Its favorite fresh food appears to be 

 the red Daphnia ; and if a cupful of these "wa- 

 ter fleas" is poured into the tank with the 

 shrimps, it is but a few seconds before the larger 

 crustaceans may be seen conveying the smaller 

 ones and eating them alive, without ceremony 

 or compunction. What causes the shrimp to 

 appear particularly happy at its meals is its 

 gay habit of displaying the food it has captured 

 or discovered, by jauntily carrying it around 

 for a time preparatory to settling down to the 

 repast. 



The shrimp will also swim about in the same 

 way with some inedible object, — a bit of debris, 

 an empty snail shell, a scrap of dead wood, a 



