Guest post: Shemaiah Kentish, George Mason University
An alevin with a orange yolk-sac attached (photo credit: fishbio.com)
An alevin is a newly hatched salmon or trout that still has its yolk-sac attached. The yolk-sac provides the alevin nourishment for the first 2-3 weeks after hatching. Typically, at this life stage, salmon or trout will stay in the gravel but they might be pushed into open water by a strong current, making them more susceptible to predation.
This Sockeye Salmon (Oncorhynchus nerka) displays a spawning kype (photo credit: Ron Harris).
Not to be confused with the popular internet phone/video chat platform of a similar name, kypes are hook like structure that develops on the jaw of some male salmonids during the spawning season. Though Skype for salmon is still far fetched, this secondary sex characteristic does, in fact, have a role in communicating sexual fitness.
Research suggests that kype size has been linked to spawning frequency, via mate choice (that is, female salmon find a hooked jaw desirable) and competition on spawning grounds (namely, battles between males where the winner gets to pass on his genes). For repeat spawners with an iteroparous reproductive strategy, the elongated jaw is reabsorbed after the spawning season ends.
Guest post by Emily Argo
Each year adult salmon migrate upstream to spawn (lay eggs) putting into motion their offsprings’ journey from hatching to making their way back to the ocean as juveniles. In addition to being a spectacular event to witness, these migrations also play a central role in ecosystem health. Over 100 different species benefit from the nutrients that the salmon provide! In order for a juvenile salmon to successfully complete their journey to the ocean and continue providing benefits to marine and freshwater ecosystems when they return to as adults, the juveniles must undergo a series of changes through a process called smoltification.
Coho salmon are one of many salmon species, their smolt lifestage is pictured here.
Smoltification occurs in anadromous species prior to entering saltwater. For example, as salmon juveniles move from their freshwater nursery habitats to the ocean, they transition from what scientists call parr to a smolt lifestage. During this transition, they change color, losing their parr bars (dark, vertical bars) and defined countershading, making them appear silvery. Their bodies also change to be more streamlined and buoyant. Even their attitudes change! While parr are typically highly territorial in shallow water, this aggression declines as the smolts move into deeper water and form shoals (large groups). During smoltification salmon smolts get a good whiff of the water to imprint on the odor of their natal stream (stream where they were born) in order to identify it during their return spawning migration as adults. Finally, how the salmon breathe (take oxygen out of the water with their gills) also changes as they go from freshwater to saltwater.
Smoltification does not begin at a specific time in all salmon species, but varies depending on temperature, latitude, size, rate of growth, age, and feeding opportunities or a combination of these factors. Since the changes that take place during smoltification are not necessarily beneficial for remaining in freshwater, the changes will reverse (desmoltification) for fish who are unable to migrate to saltwater. This is sometimes the case when there is a barrier to migration, which can cause fish to remain in freshwater throughout their lifecycle. Luckily for these individuals, salmon are equipped to survive in freshwater as long as they need to, but the inability to migrate will limit their ability to provide important nutrients to these freshwater ecosystems on their return migration as adults.
How many species of salmon can you name?
Pacific salmons are well-known examples of anadromy. They live most of their lives at sea but spawn in fresh water
An anadromous fish hatches and spawns in fresh water but spends most of its life in the salt water. This dual life cycle allows the younger fish to grow and feed in the less perilous fresh water habitats (fewer predators in the smaller systems) and the older, larger fish to grow and feed in the marine systems, where there is a greater prey base. Migrating between fresh and salt water requires complex osmoregulatory adaptations. Some species, such as Pacific salmons, only transition between fresh and salt water twice, migrating to salt water early in life and then migrating back to freshwater to spawn once and die (a semelparous reproductive strategy). Other species, such as Striped Bass (Morone saxatilis) will migrate between fresh and salt water every year to spawn (an iteroparous reproductive strategy).
For more information, check out the “CAN YOU SAY ANADROMOUS, CATADROMOUS, AMPHIDROMOUS, OCEANODROMOUS, OR POTAMODROMOUS?” post on The Fisheries Blog!
Striped bass are anadromous fish that migrate between fresh and salt water every year to spawn