Sticklebacks get Steamy at the University of Limerick!

This week at the University of Limerick, Éabha finds a spicy little species entering its breeding season with a vibrant new look.

The Three-Spined Stickleback (Gasterosteus aculeatus) is a fascinating freshwater fish that can be identified by its mottled olive colouration and the spines that run along its back. Known for its ability to tolerate a wide range of water conditions from brackish coastal waters to freshwater streams, this fish also displays a wide range of elaborate social and breeding behaviours.

A male Three-Spined Stickleback beginning to show his breeding colours.

Sticklebacks usually exhibit group behaviors, living in loose aggregations or shoals for protection against predators. In some cases, sticklebacks can show hierarchical social structures within these groups, with dominant individuals having priority access to preferred foods.

When breeding season starts in April, the eyes of male sticklebacks will turn bright emerald-blue and their throats and bellies turn a vibrant red. Males will also start to become solitary and establish territories. Despite each fish being an average of only 3-4cm long, males will defend their territories with surprising ferocity!

The tiny heart throbs will spend 5-6 hours constructing nests using plant materials, pebbles and a spit-like glue called spiggin. Once ready, males will exhibit courtship displays with fin flaring and zigzag swimming to attract females and deter rival males.

Breeding male

If successful, the female will deposit her eggs in the nest where they are then fertilized by the male. For the next 10 days, the male diligently defends the nest against intruders and continuously fans the eggs with his fins to provide the eggs with oxygen and prevent fungal growth.

After hatching, the male continues to protect and care for the young fry until they are capable of fending for themselves. Once the fry have matured, they disperse into the surrounding waters, continuing the cycle of life for freshwater sticklebacks!

The presence and abundance of three-spined sticklebacks can serve as an indicator of the ecological health of aquatic ecosystems. Their sensitivity to environmental changes such as pollution and habitat degradation make them valuable bioindicators. The sticklebacks I have been recording at UL can be found in the small stream that runs behind the PESS Building.

The surrounding woodland, grassland and vegetation acts as a crucial buffer zone around the stream, protecting it and these stunning little fish from pollution. Monitoring stickleback populations can provide valuable information about the overall health and integrity of our freshwater systems, assisting in conservation and management efforts and sounding the alarm if any damage occurs.