Bioassay Guided Fractionation and Structural Elucidation of Environmental Attractants for Juvenile European Carp (Cyprinus carpio)

Abstract

Pheromones, semiochemicals that trigger a natural response in a second member of the same species, have been extensively investigated across a variety of vertebrates and invertebrates to manipulate their behaviour. In aquatic species, these pheromones play important roles in larval settlement and metamorphosis, courtship and mating, and foraging. Pheromones responsible for the initiation of mating behaviour in carp and goldfish have been investigated extensively in sexually mature carp but there has been limited investigation on the role the environment plays on behaviour. The introduction of environmental stimuli was investigated to test the hypothesis that environmental cues can be used, like pheromones, to manipulate carp behaviour. Ceratophyllum demersum and Myriophyllum spicatum, a native and invasive aquatic macrophyte, were placed in bioassay tanks with sexually mature carp and spawning incidences recorded across a 15 min monitoring period. A clear preference for the invasive M. spicatum over the native C. demersum was observed even in the presence of yarn used as control. Crude extracts of each plant were tested using yarn as the spawning substrate with similar observations made removing the impact of the physical characteristics to the observed preference. Crude extracts of seven aquatic macrophytes collected from wetlands around Victoria where carp aggregations have been observed (Myriophyllum aquaticum, Egeria densa, Potamogeton crispus. Vallisneria australis, Cabomba caroliniana, Potamogeton sulcatus, and Chara australis) were used in behavioural bioassays mimicking those used for spawning activity to determine if juvenile carp exhibit a behavioural modification in the presence of one of these species. M. aquaticum exhibited the most significant and consistent change to preference and was selected for isolation and purification of potential attractants. In total twelve compounds were isolated and structurally identified using 1D and 2D NMR, mass spectrometry and optical rotation data. Each compound was assessed to determine the preference of juvenile carp. Eight of the twelve compounds tested resulted in a positive behavioural change and provides strong evidence that compounds derived from aquatic flora can potentially be used to manipulate carp behaviour. A final study looking at water collected from known carp aggregation hot spots at Lake Sorell in Tasmania and the Banrock Station wetlands in South Australia was conducted to see if leachates, from the surrounding environment or plants in the water, can result in similar observations. Water collected from the Silver Plains marsh at lake Sorell and the wetland outlet at Banrock station resulted in the most substantial change in carp behaviour. This observation was supported by tracking data of radio-tagged carp obtained during the periods of water collection. While no compounds were able to be successfully isolated from these samples there is potential for future work using water from the wetlands to manipulate carp behaviour. The potential to use environmental attractants to manipulate carp preferences to controlled aggregation sites, or for juvenile aggregation prior to reaching sexual maturity will contribute as part of a broad pest management program assisting in the eradication of carp in our waterways. Show more