LABORATORY EXAMINATION OF SAMPLES 



One- Meter Net Tows 



At the completion of a cruise, the eggs and 

 larvae collected in the surface hauls with the 

 1 -meter net were examined in detail. The late- 

 stage eggs and recently hatched larvae fronn 

 the hatching jars were examined, and nunnbers 

 and proportions of individuals of each species 

 determined. All eggs preserved at the time of 

 capture were measured, counted, and "staged", 

 i.e., the stage of development determined. The 

 larvae were counted and measured. Measure- 

 ments of egg diameters and hatching length 

 of the various species were made to the nearest 

 0.01 nnm. with an ocular micrometer. The 

 larger larvae were measured to the nearest 

 miilinneter . Some eggs were not staged because 

 of their extreme opaqueness, and larvae inpoor 

 condition could not be accurately measured. 

 The data for 1 -meter net tows taken on cruise 

 nos. 46, 48, and 50 are included in tables 5-7. 



Six stages, which divided the incubation period 

 into approximately equal periods of tinne, were 

 specified to enable us to estimate the age of 

 eggs at various locations: 



Stage I . --From fertilization to the formation 

 of the early blastodermal cap. 



Stage II. --From the completed blastodermal 

 cap to the development of the segmentation 

 cavity. 



Stage III. --From the appearance of the early 

 embryonic axis to the approach of the germinal 

 ring to an equatorial position. 



Stage iy.--From the equatorial position of 

 the germinal ring to just before blastopore 

 closure. 



Stage V.--From blastopore closure (half cir- 

 cle) to almost full circle (scattered pigmenta- 

 tion). 



Stage VI. --Fronn the formation of the charac- 

 teristic pigment pattern to hatching. 



Distinguishing features of embryonic develop- 

 ment in the six stages and the age in hours and 

 days for eggs developing at 38 F. are shown in 

 figure 4. 



The species composition of eggs at each 

 1-meter net station served as a guide in deter- 

 nnining the proportion of each of the species of 

 eggs picked up by the recorders on runs in the 

 general vicinity of these stations. Thus, if it 

 were found that at a certain station 70 percent 

 of the eggs were cod and 30 percent haddock, 

 this ratio was used in the species allocation 

 of eggs on the individual 2-inch sections of 

 gauze in this area. It was only necessary to do 

 this for stages I-V cod and haddock eggs, as 



the stage VI eggs usually could be separated 

 by pigmentation. This served as a check on the 

 species composition as determined by the two 

 sampling methods. 



Little difficulty was encountered in the iden- 

 tification of other fish eggs. Their character- 

 istic size, taxonomical and distributional (both 

 in time and space) differences made separation 

 relatively simple. 



The identification of larval forms of fish often 

 was difficult because of the lack of definite 

 pigment patterns at certain stages of develop- 

 ment and because of the crushed condition of 

 some specimens due to impact on the recorder 

 gauzes. In the postlarval stages, especially of 

 haddock, cod, and pollock, where the fish are 

 undergoing a transition from the larval to the 

 mature form, pigmentation patterns tend to fuse 

 making identification extremely difficult. Larval 

 fish from the time of hatching to about 10 mm. 

 can usually be separated by their distinctive 

 pigmentation pattern. Fry of about 30 mm. and 

 larger usually had assumed adult character- 

 istics. 



We found that vertebral counts, especially of 

 the abdominal vertebrae, served as an excellent 

 means of separating postlarval gadoids. 



After clearing and staining, using the tech- 

 nique described by Hollister (1934) with some 

 modifications described by Clothier (1950), the 

 following vertebral counts were made: 



Total vertebrae .-- Total number ofvertebrae, 

 excluding the urostyle (atlas through penulti- 

 mate). 



Abdominal vertebrae .-- Anterior vertebrae 

 (without haemal spines). In gadoids this is 

 synonymous with the number of vertebrae with- 

 out haemal arches. 



Caudal vertebrae . --Posterior vertebrae (with 

 haemal spines). In gadoids this is synonymous 

 with the number of vertebrae having haemal 

 arches. 



This method of identification has proved 

 extremely helpful in the classification of sam- 

 ples taken in the plankton recorder where there 

 is a tendency for the specimens to be crushed 

 or flattened beyond recognition. Fortunately, 

 the vertebrae remain intact, and it is usually 

 possible to make a count of abdominal vertebrae. 



Hardy Plankton Recorder 



In analyzing the material collected by the 

 Hardy Plankton Recorders the following pro- 

 cedures were followed: 



The gauzes were cut into divisions of four 

 sections to facilitate handling and examination. 

 The covering gauze was folded back, and both 



