612 U. S. BUREAU OF FISHERIES 
Mr. Serre. That is another thing I have left out. Since last year, 
the Bureau of Fisheries has arranged with the Lighthouse Service to 
supply the temperatures to these light vessels, as far as they go. 
Doctor Bircetow. You do not say anything about why the towing 
is so successful this year and whether there were a lot of eggs in the 
water. 
Mr. Serre. We strained the water in Massachusetts Bay from 
about the middle of May to early in July, towing close to the bottom 
and at the surface, thus getting a large number of plankton samples. 
However, there was no one to look over the material, so I went at 
it myself; spent about six weeks over it and examined only a frac- 
tion of the material, covering approximately the collections from the 
middle of June and extending over two weeks. I identified, beyond 
reasonable question, an astounding number of mackerel eggs, and 
during the last (lays the larve appeared in numbers that were 
astonishing to me. 
Doctor Biertow. Certainly, only a handful of larve. 
Mr. Serre. I got as many as 80 to 100 larvee in one sample, and 
the eggs numbered tens of thousands. 
STUDIES ON LARVAL FISHES 
By Mariez D. P. FisH 
The spontaneous remarks of visitors to the laboratory, when they peer 
through the microscope at our work, are not always complimentary. It is a 
difficult task to convince many very practical persons that a tiny thread of 
fish life—often just a few millimeters in length—can truly be of such economic 
worth that a perfectly able-bodied man or woman is justified in spending time 
upon it. Fortunately, I do not have to apologize to this group! 
It is a knowledge of that crucial period between the time when the adult fish 
is indicated merely by a few cells or an egg-confined embryo, until it ceases to 
be carried around passively by currents and tides, that gives us a key to the 
distribution of species, abundance, and the answer to many such questions, 
which we, as fisheries’ investigators, are constantly asked to solve. 
My general problem has been the identification, embryology, and distribution 
of the young of North Atlantic fishes. I place identification first, inasmuch as 
other problems are dependent, primarily, upon a determination of species. The 
work has consisted in the identification of all larval and young fishes collected 
by the various fisheries vessels in the region, a study of their early life history- 
based on these records, supplemented wherever possible by artificial fertilization 
and development experiments in the laboratory. It has been our purpose to 
study the seasonal distribution of the species that occur in this region in 
relation to physical factors, and particularly in relation to the other organ- 
isms that occur with them in the sea. Much of this investigation has formed 
a part of the problem of the early life histories of the cod, haddock, and 
pollock now being carried on by Doctor Fish. A complete knowledge of the 
life histories of all fishes forms an essential part of the bureau’s program 
in the North Atlantic. At the present time almost nothing is known concern- 
ing the early stages of many species, some of them commonly abundant. 
As to methods, the surest way to identify a larva with an adult species is, 
of course, to secure a ripe male and female, fertilize the eggs artificially, and 
study the resultant developmental stages in the laboratory. Many of the com- 
moner North Atlantic fishes have been studied in this way, and we have excel- 
lent descriptions and illustrations based upon the experiments. However, the 
possibility of keeping a larval fish alive for long after the yolk sac has been 
absorbed and the animal is actively feeding is very slight. We can not dupli- 
eate exactly their normal conditions of life in the laboratory, and, therefore, 
only early larval stages can be reared. 
The chief source of our larval-fish material is the sea itself. Gaps often 
occur in our developmental records, for certain stages can not be found by ordi- 
nary collecting methods. 
