238 



Appendices to Fifth Annual Report 



absolutely necessary to be in a position to keep the spawners for several 

 months : this can of course be easily accomplished by means of large 

 floating pens or cars, or well-boats, such as are sometimes used by fisher- 

 men. The necessity of this will be still more evident when it is mentioned 

 that only about 300,000 eggs can be 1 stripped ' from a cod at a time- 

 that, in fact, a cod takes several weeks to get rid of its spawn. 



Given plenty pure sea water and a number of ripe fish, the next desi- 

 deratum is a hatching apparatus. The form of the hatching apparatus 

 must depend on the nature of the eggs to be manipulated. While herring 

 eggs are heavy, and not only fall to the bottom, but adhere to whatever 

 they touch, the eggs of most of the food fishes are non-adhesive and 

 lighter than sea water, and hence they float at or near the surface. The 

 egg of the cod, e.g., has a specific gravity of 1*020, while the water of the 

 North Sea varies from 1-024 to 1*026 or more. Numerous hatching boxes 

 have been suggested for both heavy and floating eggs. 



I have recently designed a hatching jar for adhesive eggs, which pro- 

 mises good results. The structure of this apparatus will be readily under- 

 stood by referring to the drawing (Plate VII.). It consists of an outer glass 

 cylinder (A), in which a smaller cylinder (B), is suspended from a wooden 

 cover (C) held in position by a circle of iron fixed by nuts (a) to three 

 uprights from an iron band (b), which surrounds the neck of the outer 

 cylinder. The sea water passes along the glass tube (c) into the outer 

 cylinder, from which it escapes by the tube (d). The outer surface of 

 the inner cylinder (B) may be coated with eggs, or eggs may be placed 

 both on the outer surface of B, and the inner surface of the larger jar (A). 

 The centre of the small jar or cylinder (B) may be filled with some filter- 

 ing material, or if a low temperature is required, water from an ice chamber 

 or a freezing mixture may be conveyed into B by the lead pipe (e), and 

 allowed to escape by the pipe/* and, if necessary, the whole apparatus 

 may be introduced into an insulated wooden box, from which the water 

 from / might be conducted so as to ensure a still more equable temperature. 



For floating eggs, entirely different arrangements are required. The 

 most successful apparatus hitherto devised is the one used at Arendal. 



Through the courtesy of Captain Dannevig, I have obtained one of the 

 Arendal hatching boxes, with all the necessary fittings. The various parts 

 of this hatching box are illustrated in the accompanying plates. The 

 apparatus, which is both simple and inexpensive, consists of a wooden box, 

 8 feet in length, 2 feet 3 inches in breadth, and 1 foot deep, equally 

 divided into two by a longitudinal partition, and each of these is again 

 divided by transverse partitions into seven compartments, the five in the 

 centre being larger than the end ones. 



The whole apparatus, therefore, contains 10 large compartments (PI. 

 VIII. G) and four small ones (D). The larger compartments are not in 

 communication with each other, but the end ones are connected by an aper- 

 ture in the longitudinal partition. The first pair of compartments receive 

 the water from the inflow pipe (E) ; the last pair serve to collect the water 

 for the outflow pipe (F). 



Into the large compartments square boxes (H), adapted for floating 

 eggs, or sloping boxes (I), suitable for lobster berries, may be introduced. 



The hatching boxes (H) for the floating eggs of the cod, plaice, &c, are 

 12 inches in length, 10 inches in breadth, and 10 inches in depth (PI. IX., 

 fig. 3). The sides are made of deal fths of an inch in thickness, and the 

 bottom is made of hair netting, sufficiently fine to keep in the eggs and 

 fry, but yet wide enough to admit of a free passage of water. 



These boxes are attached by leather hinges to the transverse partitions 

 (PI. IX., AA). 



