[5J APPAEATUS FOR HATCHING SPANISH MACKEREL. K)99 



also be made tiglit by rubber packiug. The strainer must be made of 

 pure block tin, and the convex portion perforated by holes one-fortieth 

 of an inch in diameter, these holes to be as close together as the strength 

 of the tin will allow. To the extremity of strainer tube uniy be at- 

 tached rubber hose, which conveys the water olf. The glass entran(!e 

 tube passes through a piece of pine wood, so notched as to keep the 

 tube in the center of the aquarium. The clamp for exit rubber tubing 

 may be made of spring brass, and at the extremity have a thumbscrew 

 for adjusting. 



I might add that an advauatge will be found in having the aquaria of 

 the above size, which are large enough for several million Spanish 

 mackerel eggs, but were they larger it would be difficult to establish a 

 sufficient current of water, while it would be increasing rhe number of 

 aquaria needed if they were made smaller. All the parts, as you may 

 see, are such as may readily be replaced and fitted at the station. Kx- 

 perience has uot demonstrated the truth of the opinion that this foini 

 of apparatus will serve for cod hatching, but the ])r()bability is so great 

 that a trial at least might be made, with reasonable hopes of success. 



Mr. Barry suggests an automatic arrangement to keej) the water at a 

 certain height, but I see no need of additional complications. The ad- 

 vantages of this glass aquarium, arranged as described, may be summed 

 up as follows: 



1. It is inexpensive, and all the parts are easily duplicated. 



2. It furnishes a regular supply of water, the amount at our command. 



3. The eggs float without being in the least disturbed. 



4. The perforated surface of the strainer looks downward, and its cir- 

 cular slope prevents clogging by eggs or dirt ; if such, however, collect, 

 a feather readily removes without disturbing the good eggs. 



5. It is entirely of glass, save the strainer, which is of block tin, and 

 not influenced by salt water. 



In using the above apparatus the eggs may be introduced after they 

 have come up, care being taken by changing the water to free them 

 from sperm, which readily decays. After the young fishes are hatched, 

 they should be carefully siphoned into another vessel and the supply of 

 water immediately established, for the young fish need a greater amount 

 of fresh water than the eggs. I think it best to change on hatching, 

 for by this means we free the fish from the influence of the i^gg mem- 

 branes, which decay. 



Although light is absolutely necessary for the healthy development 

 of the egg and young fish, yet at no time should the sun shine directly 

 upon them. This may do in nature, but in our artificial work the snuill 

 body of water is heated, which must fall at night, subjecting the fish to 

 a change they can only occasionally survive. I might also add, the 

 mackerel are believed to spawn most freely in the afternoon, and if this 

 be true, 18 hours later the fish would be ready to hatch, and the sun 

 would not yet have acquired much power. 



