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We review various applications of biocontrol for invasive fish and aquatic invertebrates. We adopt a broader definition of biocontrol that includes traditional methods like predation and physical removal (biocontrol by humans), and modern approaches like genetic engineering and use of microbes (including pathogens). While physical removal and predation (by native predators) are used relatively commonly, use of genetic technologies and microbes is in developmental stages. The two latter strategies are most advanced in case of the common carp (Cyprinus carpio), one of the world's most invasive fish; virus release to control carp might soon occur in Australia. Drawing from empirical examples in North America, we emphasize that biocontrol strategies are most likely to be successful if they include multiple approaches that target specific behaviors or weaknesses in pests' life histories. This is illustrated by reviewing case studies on the common carp and rusty crayfish (Orconectes rusticus) in Midwestern North America. In case of the common carp, basic research on movement patterns and recruitment bottlenecks identified a strategy where winter aggregations of adults were targeted for removal with nets, while native predators of carp eggs and larvae were instrumental in controlling carp's reproductive success. In the case of the rusty crayfish, basic research on interactions between crayfish, habitat, and native predators identified a successful strategy of stocking selected native predators to control juvenile crayfish in conjunction with physical removal of adult crayfish using traps. We are also reviewing the case of the round goby (Neogobius melanostomus) in the Great Lakes. In this example, multiple pieces of evidence (diet, bioenergetics) illustrate how initially abundant pest was brought under control (in some areas) by several species of native predators in a large, natural ecosystem. Overall, examples of successful biocontrol of aquatic pests have been rare and have relied on physical removal and predation. We expect that new technologies (e.g. genetic technologies) will occur in the next decade but will have to clear regulatory and ethical concerns before they are applied. While developing more sophisticated control techniques, we advocate for more basic research on the life history of the pests to identify behavioral or developmental weaknesses that could be targeted with specific tools to increase chances of success while minimizing impacts on native ecosystems. [ABSTRACT FROM AUTHOR]

In lakes of the Upper Mississippi River Basin (UMRB), invasive common carp (Cyprinus carpio) employ a reproductive strategy in which adults migrate out of lakes to spawn in seasonally unstable marshes that have few egg and larval predators. The rates with which the juveniles outmigrate from marshes into adjacent lakes have critical management implications but have not been quantified using direct approaches. We used passive integrated transponder (PIT) tags to quantify outmigration of young-of-year (YOY) carp from marshes into lakes in two systems in UMRB. In both cases, marshes were located upstream of lakes and PIT antennas continuously monitored the movement of carp. In the first system, which we monitored for three years, 0.2% to 5.5% of PIT-tagged YOY carp outmigrated to the lake each year; highest outmigration occurred during mid-summer periods of low water level in the marsh. In the second system, which comprised much more extensive area of deeper marshes, 0.2% of YOY carp outmigrated to the lake. Ageing and mark-recapture analyses confirmed that relatively few YOY carp recruited into the lake populations from the marshes each year (between 5 and 50 per hectare). Our results show that YOY carp outmigration rates are low (< 6%) but can vary an order of magnitude among years. These findings are important for removal-based management strategies for carp in lakes of UMRB by showing what adult removal rates are needed to compensate for juvenile recruitment from marshy nurseries. [ABSTRACT FROM AUTHOR]

Across-ecoregion analyses showed that the recruitment of common carp, Cyprinus carpio (Linnaeus 1758), a globally invasive fish, is strongly influenced by lake productivity: while recruitment was frequent in hypereutrophic lakes, it was invariably absent in oligotrophic lakes. This led to a hypothesis that common carp larvae might have faster growth rates in productive lakes that allow them to outgrow native predators, whereas larvae might encounter nutritional bottlenecks in oligotrophic lakes. We shed some light on this hypothesis by documenting how zooplankton communities found in oligo-, meso-, and eutrophic lakes in Minnesota, USA affected larval carp survival, growth and diet composition. We cultured larval carp in tanks fed zooplankton at naturally occurring densities from three lakes of varying trophic states for 20 days during two consecutive springs. The growth rates were significantly higher (up to 5 times) among larvae fed zooplankton from the eutrophic lake and lowest in larvae fed zooplankton from the oligotrophic lake. Despite their small size (~6 mm), carp larvae selected large zooplankton (0.3–0.6 mm), primarily Bosmina spp., even on the first day of exogenous feeding. This pattern was consistent across all treatments. Rotifers were generally not found in the stomachs of larval carp, despite their high abundance, even if other food items were scarce. The densities of cladocera were highest in the productive lake, especially during one of the two years when larval carp showed very rapid growth rates. Our study shows that larval carp have well defined dietary preferences and that common carp recruitment might be especially likely to occur in productive systems with abundant cladocera populations in which carp larvae are expected to be more likely to escape gape-limited, native predators. [ABSTRACT FROM AUTHOR]