Design and validation of artificial feeders to study feeding preferences and growth of hematophagous juvenile sea lamprey (Petromyzon marinus)

The parasitic and invasive land-locked sea lamprey Petromyzon marinus populations contributed to the collapse of the Great Lakes fisheries in the mid-1900s, while native anadromous populations are currently under threat and require conservation efforts for protection. Despite the increasing concern for both populations of this species, the juvenile stage of the sea lamprey’s life cycle has not been well studied. This is due, in part, to ethical concerns raised around holding live host fish with juveniles and the lack of an alternative feeding method to maintain these juveniles in the laboratory. The feeder should be designed to minimize fouling of the water with blood, and trigger juvenile sea lamprey to volitionally feed at comparable rates to naturally feeding fish. Two artificial feeder prototypes were developed that used porcine blood in lieu of using host fish body fluids to study the feeding physiology and behaviour of juvenile sea lamprey. The first feeding system, the ‘Porto’ feeder, consisted of a feeding plate that uses umbrella-type microvalves to regulate flow from a food reservoir. The second feeder was a hollow silicone fish with self-sealing perforations filled with the liquid meal. The artificial feeders were developed to make use of the suctorial feeding mechanism of the juvenile sea lamprey which generates a negative pressure. Both feeder types were capable of delivering a liquid meal to an attached juvenile sea lamprey but volitional attachment by the juvenile sea lamprey only occurred with the silicone fish. When placed into the silicone fish, porcine blood was the only liquid meal found to encourage volitional attachment compared to liquid meals that incorporated fish (Pangasius bocourti) fillet extract. When manually force fed, ration size of the liquid meal did impact the amount of blood consumed by the juvenile sea lamprey. Absorption of the iron from porcine blood likely occurred in the anterior intestine while secretion of excess iron occurred in the posterior intestine. Unfed animals had higher amounts of iron in the liver compared to fed animals, indicated by the iron staining intensity. This suggests that the fed animals mobilized the iron in the liver to aid in the growth observed in other studies during feeding or for the purposes of elimination during feeding. The decision-making maze task (Y-maze) showed no preference towards bile salts from rainbow trout (Oncorhychus mykiss) compared to the control. However, neither positive (trout water) nor negative (lamprey homogenates) controls elicited expected responses either. Thus, whether fish-related olfactory cues may enhance artificial feeding systems is inconclusive at this point. The silicone fish has demonstrated its use in the laboratory setting based on behaviour and attachment rates and should be considered for use when feeding juvenile sea lamprey in the laboratory. Although volitional attachment did not occur with the Porto feeder, it may be useful when performing feeding studies with juvenile sea lamprey where the liquid meal can be dosed with other compounds. In conclusion, although the silicone feeder prototype requires additional optimization, it is a viable system to deliver a blood meal to parasitic lamprey for laboratory and potentially field application without the need of a live host. This will aid future research on this problematic life history stage