Brown bullhead catfish (Ameiurus nebulosus) are an invasive freshwater fish widely recognised as a threat to New Zealand’s aquatic ecosystems. Early detection of new incursions increases the chances of eradication or control, but current survey methods such as netting and electrofishing are expensive and time consuming when fish are at low abundances. Domestic dogs (Canis familiaris) have previously demonstrated the ability to detect the presence of catfish in laboratory water samples, while discriminating against non-target species. The aim of this research was to investigate whether scent detection dogs could plausibly be employed in aquatic biosecurity programmes. The first experiment used a probe design to determine the scent-detection limits for catfish biomass under laboratory conditions. Water samples taken from tanks containing a standard catfish biomass concentration of 15.5 g/L (equivalent to 38,700 kg/ha) were assessed by the dogs and progressively diluted following the successful attainment of identification and discrimination criteria. All three participating dogs were able to detect the presence of catfish at biomass concentrations ≤12.6 kg/ha, with one dog achieving 4.6 kg/ha. Concurrently, the dogs were also able to successfully discriminate against a goldfish (Carassius auratus) distractor scent indicating that they are able to distinguish specific species of fish in the environment. The effects of sample preservation on dogs’ ability to identify and discriminate target scents have rarely been investigated. In practice, field samples from the environment would likely necessitate the preservation of samples prior to assessment by dogs. A second study used a repeated-measures reversal design to investigate dogs’ abilities to detect catfish at a standard biomass concentration of 310 kg/ha which had been refrigerated or frozen for up to 1-week. No statistically significant difference in hit rates between unpreserved (baseline 1: 93%, baseline 2: 98%), refrigerated (97%), and frozen (96%) samples was apparent; (F(3, 6) = 2.061502, p = 0.2069). These results indicate that dogs are capable of detecting and discriminating the scent of catfish at biomass concentrations typical of many freshwater ecosystems in the Waikato region. Further, limited periods of freezing or refrigeration appear to have no significant effect on the scent-detection abilities of dogs. Future research needs to be conducted with field samples from lakes and could explore the effects of preservation on low biomass concentrations. The results from this study are promising for the potential future employment of scent detection dogs in aquatic biosecurity monitoring.