DISTRIBUTION OF EGGS AND LARVAE OF JACK MACKEREL 



277 



Settb, Oscar E., and Elbert H. Ahlstrom. 



1948. Estimation of abundance of the eggs of the 

 Pacific pilchard (Sardinops caervlea) off southern 

 California during 1940-41. Journal Marine Re- 

 search, vol. 7, no. 3, p. 511-542. 



South Pacific Fishery Investigations. 



1952. Zooplankton volumes off the Pacific coast, 



1951. U.S. Fish and Wildlife Service, Special 

 Scientific Report: Fisheries No. 73, 37 p. 



1953. Zooplankton volumes off the Pacific coast, 



1952. U.S. Fish and Wildlife Service, Special 

 Scientific Report: Fisheries No. 100, 41 p. 



1954. Zooplankton volumes off the Pacific coast, 



1953. U.S. Fish and Wildlife Service, Special 

 Scientific Report: Fisheries No. 132, 38 p. 



1955. Zooplankton volumes off the Pacific coast, 



1954. U.S. Fish and Wildlife Service, Special 

 Scientific Report: Fisheries No. 161, 35 p. 



Turner, C. Donnell. 



1948. General endocrinology. W. B. Saunders Co., 

 Philadelphia and London, 604 p. 

 Walford, Lionel A. 



1948. The case for studying normal patterns in 

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 7, no. 3, p. 505-510. 



APPENDIX 

 A. FISH EGG INCUBATOR 

 Description 



When estimating the total abundance of pelagic 

 fish eggs it is necessary to know the rate of develop- 

 ment. Since this parameter varies with tempera- 

 ture it has been customary in the past to compute 

 a regression of log hours of development against 

 temperature in tenths of a degree centigrade. This 

 indirect method, while very accurate, is extremely 

 laborious and time consuming. A more direct 

 method was desired, and \vith this need in mind, 

 an incubator was designed for use at sea. 



Since most of the biological material is taken 

 well offshore, and since hatching times are rela- 

 tivelj' short, it is necessary to work at sea. Some 

 of the many technical problems that are peculiar 

 to sea work and their solutions are described here. 



The pitch and roll of ships cause delicate equip- 

 ment to be damaged quite easily, and the need for 

 sturdy construction is readily apparent. Instru- 

 ments such as this one should be portable, since 

 they have a limited use and cannot be left aboard 

 research vessels indefinitely. A compromise be- 

 tween sturdy construction and portability of an 

 egg incubator was effected by resorting to a double- 

 box construction, using marine pljnv'ood. The 

 temperature-sensing and temperature-control de- 

 vices were of a mechanical nature. A heavy duty, 



stainless steel sensing element enclosing a mercury 

 colmnn was employed. The mercury column ac- 

 tivated a mechanical linkage in the thermostat, 

 which in turn opened and closed an electrical 

 switch. The circulating pump and cooling device 

 were remote from the incubator itself, but con- 

 nected by garden hoses (appendix fig. 1). The 



RUBBER GASKET 



THERMOSTAT 



INFLOW 



TEMPERATURE 

 ,.««tl» ^ SENSOR 



WATER BATH 

 JAR RACK 



OUTFLOW 



CLAMP 

 LOCK 



PUMP a 

 COOLING UNIT 



Appendix Figure 1. — Fish egg incubator. 



separation of units contributed to the portability 

 of the instrument. 



Corrosion from the salt air which attacks most 

 metals was controlled by using a synthetic resin 

 paint on all exposed parts of the incubator. Other 

 structures were concealed in corrosion resistant 

 housings. 



Temperature control (± 0.2° C. of selected tem- 

 perature) was obtained by using the main water 

 mass in the water bath as a heat reservoir. As the 

 water mass warmed, the change in temperature 

 was recorded by the sensing element and the water 

 routed through the cooling mechanism. It was 

 believed that temperature changes in the incuba- 

 tion chambers were small, because the main water 

 mass was so large, by comparison, that a large 

 amount of heat would have to be transferred before 

 anj^ appreciable temperature change in the incu- 

 bation chambers would occur. 



