Objectives
After participating in this activity, students will be able to:
- Describe and illustrate scientific concepts such as the stages of the fish life cycle
- Diagram progression from egg, larval fish, fry, juvenile, adult
- Examine two general animal reproductive strategies
- Compare and contrast the reproductive strategies of at least two Great Lakes fish
Summary
Like all animals, fish need to survive and grow large enough to reproduce. Fish that survive to spawn use a range of strategies to ensure successful reproduction.
Background
Each fish species has a unique reproductive strategy and favors certain habitats for spawning and for early development of their newly hatched young. Many Great Lakes fish can be found in shallow water during part of their life cycle. Many species use shallow waters of lakes or rivers as spawning habitat either in the spring or fall. Some, such as northern pike, prefer wetlands with aquatic vegetation. Others such as lake whitefish prefer shallow reefs, which provide rich areas for food and rocky structure to protect the eggs and later the fry.
Fish life cycles vary among species. In general, however, fish progress through the following life cycle stages:
- Eggs: Fertilized eggs develop into fish. Most eggs do not survive to maturity even under the best conditions. Threats to eggs include changes in water temperature and oxygen levels, flooding or sedimentation, predators and disease.
- Larval fish: Larval fish live off a yolk sac attached to their bodies. When the yolk sac is fully absorbed the young fish are called fry.
- Fry: Fry are ready to start eating on their own. Fry undergo several more developmental stages, which vary by species, as they mature into adults. Young fish are generally considered fry during their first few months (during their first few months to less than one year in some species).
- Juvenile: The time fish spend developing from fry into reproductively mature adults varies among species. Most fish do not survive to become adults. Threats to survival include fluctuations in water temperature, changes in oxygen levels, competition for habitat, and predators.
- Adult: When fish are able to reproduce, they are considered adults. The time it takes to reach maturity varies among species and individual fish. Fish with shorter life spans reach maturity faster. For example, female round gobies mature in approximately one year and live for two to three years. Lake sturgeon can live from 80-150 years, but females don’t reach maturity until they are approximately 25 years old.
- Spawning: Female fish release eggs into the water (either into the water column or into a nest) and male fish fertilize eggs by releasing milt. Not all eggs are fertilized. Some fish spawn each year (or every one or more years) after reaching maturity, while others spawn only once and then die.
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