The use of reproductive chemical cues is widespread amongst fishes. However, the most understood sex pheromone systems derive from species that employ a scramble spawning reproductive strategy. This thesis investigated for the first time the use of reproductive chemical communication in topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel) and sunbleak Leucaspius delineates (Heckel) that use two different forms of a male nest guarding reproductive strategy. In topmouth gudgeon, approximately a third of reproductive females adopted a body posture in response to reproductive male conditioned water advertising high receptivity to potential mates. Electro-Olfactory Gram recordings of reproductive male and female topmouth gudgeon revealed a high magnitude response to reproductive male and female odours. In addition, both topmouth gudgeon and sunbleak reproductive females responded to chemicals cues derived from conspecific reproductive males by an increase in swimming behaviour. In contrast to male topmouth gudgeon, reproductive male sunbleak responded to chemical cues from reproductive conspecific males and females. Active compounds were isolated from reproductive male topmouth gudgeon conditioned water by two different methods solid phase extraction (C-18 cartridges) and using a freeze drier. The eluate was subsequently separated using High Performance Liquid Chromatography into retention time fractions. An active fraction was identified using a bioassay guided separation. Nuclear Magnetic Resonance analysis showed that compounds were present in the active fraction. Chemical interaction between topmouth gudgeon (invasive to Europe) and sunbleak (native to Europe) was also investigated. Behaviour responses in the two species were asymmetrical topmouth gudgeon did not respond to sunbleak chemical cues. In contrast, both reproductive female and male sunbleak responded to topmouth gudgeon chemical cues. The results show that reproductive chemical communication is in operation in both test species. The cross species interaction indicates that pheromone pollution may represent an additional impact of non-native species introductions.