MANUAL OP FISH-CULTURE. 201 



but they can rarely be induced to eat. A certain percentage of th© 

 penned fish die and are removed at once from the cars. The develop- 

 ment of the sexual organs is noted when the dead fish are taken out. 

 Fish about ready to spawn are placed in a separate car and carefully 

 watched. They are examined two or three times a week and any ripe 

 eggs are taken. 



In taking and fertilizing the eggs of brood cod the same general 

 methods are followed as are adopted on the fishing vessels in Ipswich 

 Bay. The spawn-taker grasps the ripe fish near the tail with his left 

 hand and holds the fish's head either between his body and left arm or 

 between his thighs, using his right hand to strip the fish. The eggs 

 are usually taken in a bucket. Both the dry and wet methods of fertil- 

 ization are used at Woods Hole. Usually about 80 per cent of the eggs 

 taken are fertilized. Unlike many other fishes artificially propagated, 

 the cod does not yield all of its eggs at one time. After expressing all 

 the eggs possible from a given fish, it is returned to the live-car, and in 

 a few days will have matured more eggs, which are then taken. When 

 the ovaries have discharged all their eggs, the fish is released. 



In recent years from 1,6U0 to 9,000 cod have been penned annually 

 in the protected basin at Woods Hole. Only from one ninth to one- 

 third of these, according to the season, yield good eggs. 



CHARACTERISTICS OF COD EGGS. 



Cod eggs are nearly transparent, and float at the surface of the water 

 when first taken. They vary in color from a pale green to a deep red, 

 those having the green color being tlie best. Good results are seldom 

 obtained from the red eggs, and those of a deep red color almost invari- 

 ably die in three or four days after being received. Unless the density 

 of the water is low, the eggs normally float during the entire hatching 

 period. However, it frequently happens that, owing probably to the 

 accumulation of sediment, the eggs gradually sink during the last third 

 of the incubation period, and finally mass together on the bottom of the 

 hatching-box; here they would quickly smother but for the current. 



Floating eggs are not necessarily good ones, for unfertilized and 

 injured eggs usually float 18 to 36 hours before going to the bottom. 

 Unfertilized eggs may be readily detected, as they have no disc which 

 marks fertilization and have a milky appearance. Th»e dead eggs 

 quickly sink, and are easily distinguished from the sound eg^s by a 

 white spot in the center. 



Eggs received at the hatchery are transferred from the vessels in 

 which they came to Chester jais partly filled with water, and in 10 

 or 15 minutes they rise to the surface in a dense mass. Tl>e eggs are 

 put in each Jar to the depth of an inch, a (juantity representing ai)prox- 

 imately 370,000 eggs, if the hatchery is full, about a fifth more eggs 

 may be put in a box, the maximum number that may be safely carried 

 being 450,000. The first measurements are carefully made, as they form 

 the basis for subsequent estimates. As soon as the eggs ai'e measured 

 they are transferred to the hatching-boxes with dippers. 



