278 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The eggs were incubated in pint or quart mason 

 fruit jars. The pint jars had glass tops held in 

 place by a spring clamp; the quart jars were wide- 

 mouthed and equipped with plastic lids. 



Procedure for use 



While the vessel is still at the dock, the incu- 

 bator and cooling mechanism are secured to the 

 deck. The water bath is filled with fresh water 

 (which causes less corrosion in the cooling system 

 than salt water) and the circulating and cooling 

 motors are started. Operability of the thermostat 

 is checked. 



Once the vessel is in the collecting area, the 

 thermostat is set so that the water in the water 

 bath assumes the same temperature as the sea. 

 Later on, at the time the biological sample is re- 

 ceived, a bathythermograph reading is taken and 

 the thermostat adjusted. The fruit jars are filled 

 with sea water from the area and the samples 

 placed in them. A small air space is left at the 

 top of the jars to aid aeration of the sample. The 

 jars are then placed in the jar rack and locked into 

 place. From then on the operation is automatic, 

 although temperature readings should be taken 

 frequently to assure that the incubator is operating 

 properly. 



General specifications 



The outside dimensions of the incubator were 

 32 inches by 32 inches by 35 inches deep. The 

 inside dimensions, the perimeter of the water bath, 

 were 26 inches by 26 inches by 26 inches. Both 

 the inside and outside boxes were made of 5^-inch 

 marine plywood fastened together with brass 

 screws. The space between the boxes was filled 

 with an insulating material. The inside box was 

 lined with copper sheeting that had been soldered 

 at the joints and was therefore watertight. The 

 jar rack also was made of copper. The individual 

 chambers of the bottle rack were 4 inches square 

 and accommodated either pint or quart wide- 

 mouthed jars. 



The copper lining was pierced by three holes: 

 one for inflowing water, one for outflowing water, 

 and one for the temperature-sensing element. 



The lid was fastened by two heavy metal strap 

 hinges and tliree clamp locks. A sponge-rubber 

 gasket prevented leakage. 



The water in the water bath was circulated by a 

 Jabsco pump and cooled by a Temprite cooler. 

 The temperature control was maintained by a 

 Partlow thermostat. Two j4-inch plastic garden 

 hoses with brass fittings connected the pump and 

 cooler with the water bath. All exposed surfaces 

 were painted with green plastic paint. 



B. STAGING SCHEME OF JACK MACKEREL 

 EGGS 



Stage I. — Unfertilized eggs or fertilized eggs be- 

 fore cell division. 



Stage II. — Begins when the first cell becomes 

 visible on the yoke and ends at the completion 

 of blastodisk formation (at about the 256-cell 

 stage). 



Stage III. — Starts at the completion of blastodisk 

 formation and terminates when the germ ring 

 has migrated to its greatest diameter (half-way 

 up the egg). 



Stage IV. — Begins as the germ ring moves up- 

 ward over the greatest diameter and ends when 

 the germ ring lies over the oil globule, prior to 

 blastopore closure. 



Stage V. — Begins at blastopore closure and ter- 

 minates when the tail bud starts to separate 

 from the yolk. 



Stage VI. — Begins when the tail bud becomes free 

 of the yolk and ends when the caudal one-eighth 

 of the body is free of the yolk. 



Stage VII. — Begins when the caudal one-eighth 

 of the body is free of the yolk and ends when 

 the caudal one-quarter of the body is free of the 

 yolk. A finfold is visible. 



Stage VIII. — Begins when the caudal one-quarter 

 of the body is free of the yolk and the tip of the 

 tail approaches the chin. The tail portion of 

 the embryo begins to rotate out of the em- 

 bryonic plane and the finfold is moderately 

 wide. 



Stage IX. — This stage is characterized by the tip 

 of the tail laterally approaching the head. The 

 oil globule comes to lie in the anteroventral 

 portion of the yolk sac. The finfold is wide and 

 fuUy formed. This stage terminates when the 

 embryo hatches. 



Disintegrate. — Includes all jack mackerel eggs 

 whose internal structure is such that staging is 

 impossible. 



