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Dispatches from the field

Scientists seek out the tiniest catch, larval fish in the Gulf of Alaska


grouping of larval arrowtooth flounder, Pacific cod, pollock and sablefish
Photo: Ali Deary / Rebecca White, NOAA Fisheries

Larval Fish
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The curious transformation of fish: larvae to adults

May 23, 2017 -- Have you ever wondered what young fish look like before they arrive on your plate as an adult? Larval fish and adult fish often look very different. So far, we have successfully caught fish larvae at all 51 stations we have sampled and many of the species we have encountered are commercially important. We’ve found walleye pollock, rockfish, sablefish, arrowtooth flounder, Pacific cod, Pacific sand lance, and slender blacksmelt.


larval slender blacksmelt
Larval slender blacksmelt   Photo: Ali Deary, NOAA Fisheries


We have also caught some squid, krill, and copepods.

This is my first trip sampling larval fishes in Alaska so I am eagerly sorting through our catch after every net haul! I saw many of the species we are catching now about eight years ago when I was a summer intern working with the Center’s Groundfish Assessment Program. We only caught adults during those trips. Now, I am revisiting the region and looking at the earlier stages of fish and many of them look very different from the adults.


larval squid
Larval squid   Photo: Ali Deary, NOAA Fisheries


Newly hatched larvae do not yet have fins and their bodies are transparent. However, as they develop, the young fish will transform and begin to resemble the adults. Similar to a caterpillar maturing into a butterfly, many larval fish metamorphose and do not resemble the adult form until they are juveniles. It is as juveniles that fish develop fins, scales, and coloration similar to adults. When this transformation happens varies by fish species but for most of the species we are researching, it occurs early, during the first few months of life.

We are interested in studying the early stages of fish because their habitat needs can be extremely different from the adults. For example, adult sablefish (also known as black cod) live along the bottom at depths up to 1,500 meters -- that is equivalent that is equivalent to more than eight Space Needles stacked on top of each other. The larvae and juveniles live in the top few meters of the water.

We know a lot about the adults but we know very little about the earlier stages, which are the most sensitive times for a fish. We continue to learn about what larvae need from their habitat in order to survive and reach adulthood. That is why during this survey we classify the larval fish species we encounter and record the temperature of the water, how salty it is, and what food is available to the larvae. With these data, we can identify the various habitat needs of fish larvae and determine how their needs differ from the adults in order to understand the factors that affect survival in the early stages.

Post by: Ali Deary


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