410 
BULLETIN OE THE BUREAU OF FISHERIES 
Table 4. — Rate of growth of 9,011 pigfish during their first summer 
Month 
Fish 
measured 
Smallest 
Largest 
Average 
Month 
Fish 
measured 
Smallest 
Largest 
Average 
March ... 
April., --- 
May . 
June 
July- - 
15 
571 
1,580 
2, 188 
1,608 
Mili- 
meters 
2.5 
2.5 
2.0 
2.0 
10.0 
Mili- 
meters 
7.0 
12.0 
27.0 
80.0 
112.0 
Mili- 
meters 
4.3 
6.2 
5.6 
18.6 
57.4 
August.. 
September 
October . 
November 
1,656 
482 
326 
585 
Mili- 
meters 
25.0 
60.0 
80.0 
87.0 
Mili- 
meters 
145.0 
155.0 
156.0 
157.0 
Mill- 
meters 
85.9 
106. 1 
116.6 
I 108. 7 
1 Decrease in average length explained in text. 
The almost total cessation of growth indicated in the graph (fig. 39) of the largest 
fish for October and November and a decrease in the average length of all fish measured 
in November, while the smallest fish apparently were still growing rather rapidly, 
seems to require an explanation. The number of fish taken and measured during 
September, October, and November is not large (see Table 4), yet the catches are 
believed to represent fairly accurately samples of the fish present. In other words, 
the methods of collecting, mostly with the otter trawl, did not differ from those used 
the previous months and are believed to have been successful in taking representative 
samples. It has been shown that the larger fish appear to leave the local waters 
earlier than the smaller and jmunger fish. Since fewer and fewer large fish appeared 
in the catches, it would seem as if the earlier exodus of the larger fishes extended down 
to the O class and that the larger fish of the season were migrating in October and 
particularly in November, whereas the smaller ones remained in the shallow waters 
somewhat later. These migrations appear to explain why the growth curve (fig. 39) 
shows virtually no increase in the length of the largest fish taken during October and 
November. They also explain the decrease in the average length of all fish taken, 
from 116.6 millimeters in October to 108.7 millimeters in November, even though the 
graph shows an increase in the length of the smallest fish of the O class from 80.0 
millimeters in October to 87.0 millimeters in November. 
According to the data presented herewith (Table 4 and fig. 39) the earlier and fast- 
est growing young may reach a length as great as 157 millimeters (about 6% inches) 
during their first summer, whereas the later and smaller young of the same season 
apparently are only 87 millimeters (3 % inches) long. Growth does not appear to 
proceed rapidly after the fish withdraw from the local waters, as already pointed out, 
for the smallest individuals definitely assigned to the I class in June were only 105 
millimeters long. The length of the largest representatives of the same year class at 
this time was not definitely determined, because of insufficient data. However, a 
frequency curve indicates it to be near 180 millimeters. 
AGE AT SEXUAL MATURITY 
The smallest sexually mature pigfish observed were from 8 to 8% inches (200-215 
mm.) in length. It may be concluded from this fact and the data presented in the 
preceding paragraph that the fish of the I class are too small to spawn, the largest 
being only about 7 % inches in length in June, at the end of the spawning season; and 
it seems certain that sexual maturity is not reached until the fish are about 2 years 
old. This conclusion was arrived at by Taylor (1916, p. 321) also, who based his 
conclusion mainly on the study of scales. Taylor found a great diminution in number 
after the age of 2 years, and he believes that many of the fish may perish after the first 
spawning. According to this author, comparatively few pigfish reach an age of 3 
years and very few 4 years. 
