Salmon Anatomy and Dissection w/ PSF Biologist, Nicole Frederickson

Summary

Nicole Frederickson, a biologist with the Pacific Salmon Foundation, demonstrates the external anatomy and internal organs of male and female pink salmon. She explains how each feature helps the fish survive, move, or reproduce, and guides viewers through a dissection and a matching-diagram activity.

External Anatomy

Spawning-related differences

Male and female pink salmon look similar in the ocean, but change as they return to spawn. Males develop a hump on their backs and a hooked jaw, which may help them compete with other males. Females do not develop these features.

Features and functions

• Operculum: The fleshy flap covering the gills. It protects delicate gill tissue.
• Lateral line: A sensory system running along the fish’s side. It detects movement and vibrations in the water, helping salmon sense predators or prey and keep track of nearby fish.
• Fins: Fins generally help with movement, steering, balance, and stability.
  • Dorsal fin: Helps stabilize the fish and make sudden turns.
  • Adipose fin: A small fin behind the dorsal fin. The presenter says it may have a sensory role and may help with maneuvering in fast or turbulent water. Hatcheries clip it from young fish, so its absence can indicate a hatchery-raised salmon.
  • Caudal fin (tail): Helps steer the fish.
  • Anal fin: Helps with stability and balance.
  • Pelvic fins: Paired fins used for steering, balance, and stabilization.
  • Pectoral fins: Paired fins used for steering and balance, and for moving up and down in the water.

Dissection and Internal Anatomy

The demonstration begins by removing the operculum to expose the gills. The presenter then opens the body cavity with a cut from the vent toward the front of the fish, taking care not to cut into the stomach. Viewers are invited to locate and cut out corresponding organs on a salmon diagram.

• Gills: Extract oxygen from water passing over them. Gill rakers—the pale, tooth-like structures—help direct food toward the stomach rather than out through the gills.
• Liver: Produces bile, stores energy, helps detoxify blood, and contributes to nutrient absorption and hormone production.
• Heart: Pumps blood toward the gills and around the body. The subtitles describe it as having four chambers; fish hearts are generally two-chambered, so this detail may be an error in the transcript or presentation.
• Stomach and pyloric caeca: The pyloric caeca are finger-like structures surrounding the stomach. They increase surface area and help with digestion and nutrient absorption. The presenter notes that salmon stomachs are relatively small.
• Testes: The male gonads, which produce sperm.
• Ovaries and eggs: The female gonads contain her eggs. The presenter says female pink salmon typically carry about 1,000–2,000 eggs.
• Spleen: Identified during the dissection, but its function is not explained in the subtitles.
• Intestine: Moves digested food toward the vent for excretion and is a major site of nutrient absorption.
• Gallbladder: Stores bile produced by the liver. Bile helps the intestine digest fats. The presenter says the gallbladder’s color and fullness can indicate when the fish last ate: yellow and nearly empty suggests within about 24 hours, while bluish-green suggests roughly a week. The dissected fish had little food in its stomach, which the presenter attributes to salmon eating less as they return to spawn and use energy for reproduction.
• Kidneys: The presenter describes an anterior kidney involved in producing blood cells and hormones, and a posterior kidney that balances salt and water.
• Swim bladder (also called the gas or air bladder): A gas-filled sac that helps the fish maintain buoyancy and adjust its position in the water.

The female dissection shows the same general internal organs as the male, but with eggs rather than testes. The video concludes by showing how to place the male or female reproductive organs in the appropriate locations on the diagram.

Speakers and Sources Featured

• Nicole Frederickson: Biologist with the Pacific Salmon Foundation; presenter and dissection guide.
• Pacific Salmon Foundation: The organization Nicole identifies as her employer.