Construction of artificial river and lake banks changes the aquatic environment, and these changes are known to cause decreases of aquatic plants in shallow waters. We conducted experiments to examine the involvement of aquatic plants in spawning behavior of goldfish, Carassius auratus, and cruicuan carp, Carassius buergeri subsp.2. The spawning behavior was induced by injecting prostaglandin F2α into females. Pairs of male and female goldfish or crucian carp were placed in experimental tanks with or without aquatic plants made of acrylic yarn. Both goldfish and crucian carp spawned actively onto the aquatic plants whereas the behavior significantly decreased without the aquatic plants. The present experiments demonstrate that aquatic plants are essential as spawning substrates for performance of spawning behavior of these species. It is critical for conservation of fish species that use aquatic plants as spawning substrates to maintain aquatic plants on river and lake banks.
