Fish Families Grow in Spring
Spring has arrived, signaling the start of another season of life for many fish species living in the Credit River.
Fish require a complex set of conditions to reproduce, known as spawning. Factors such as water temperature, day length, flow levels and habitat availability can all affect the timing of spawning. These conditions can differ widely across species.
Through our long-term monitoring, we track these changing conditions in our rivers and streams to better understand when and where fish are spawning. This helps us identify trends over time and determine what conservation actions are needed to protect spawning habitat and support overall watershed health.
Let’s take a closer look at some spring fish spawning examples from the Credit River Watershed.
Bluntnose Minnow
The bluntnose minnow (Pimephales notatus) is a cavity-nesting fish that spawns beneath rocks or logs in streams and rivers. During breeding season, males use their snout and tail to clear sediment from the underside of these surfaces, creating a clean space where females can lay eggs. Because good nesting sites can be limited, several females may use the same spot.
After spawning, the male guards the nest and fans the eggs with his fins to keep them clean and oxygenated until they hatch, usually within about two weeks. Spawning typically begins once water temperatures reach 19 to 28 degrees Celsius, and males develop darker, bluish colouring during this time.
River Chub
When water temperatures are between 15 and 20 degrees Celsius, river chub (Nocomis micropogon) lay its eggs on rocky substrates, which are a hard, non-shifting foundation that provides a stable surface. Males collect small stones with their mouths to create a large mound with lots of nooks and crannies to hide eggs in. The larger the pile he creates, the more attractive he is to potential mates. Once he’s enticed females to nest in his masterpiece of small stones, the hidden eggs typically hatch in five to six days. These leftover rock nests are often used by other spawning species, like the common shiner.
Western Blacknose Dace
The western blacknose dace (Rhinichthys obtusus) is a small minnow that spawns over rocky streambeds. During breeding season, males develop a bright orange stripe along their sides and darker mottling on their backs, while females remain shades of brown. Females scatter their eggs in shallow gravel, where they settle between stones for protection. Spawning typically occurs when water temperatures range between 12 and 27 degrees Celsius.
Northern Hog Sucker
The northern hog sucker (Hypentelium nigricans) is another species that prefers rocky substrates for spawning when water temperatures are 16 to 22 degrees Celsius. Adults gather in suitable habitats and stir up the bottom with their fins and tails. Eggs settle in the small depressions that are created in the gravel and are left unprotected until they hatch in roughly 10 days, making them susceptible to predation by some of the other species mentioned above.
Iowa Darter
The colourful Iowa darter (Etheostoma exile) attaches its eggs to aquatic plants. Rather than carefully depositing eggs like the bluntnose minnow, females of this species scatter eggs so they stick to submerged plants or roots. Neither parent will protect the eggs once laid, leaving them undefended for up to 20 days before hatching. This species prefers chillier water temperatures for spawning between 12 and 16 degrees Celsius.
Another Season of Monitoring
In 2025, we surveyed the fish communities at 42 sites across the Credit River Watershed, ranging from small tributaries to large sections of the main Credit. Amazingly we documented 37 species. Since the inception of the Integrated Watershed Monitoring Program in 1999, we have surveyed over 270,000 individual fish. This information is used by other teams within Credit Valley Conservation and by our municipal and provincial partners, academic institutions and watershed residents to guide management decisions, conservation actions and support aquatic research.
As temperatures warm, we’re excited to get back in to the field and monitor these species through our Integrated Watershed Monitoring Program (IWMP).
Visit our Open Data Portal where you can view the data yourself and learn more about our monitoring program.
Share your fish photos with us on Instagram, Facebook and X.
By McKayla Jarvie, Watershed Monitoring Technician