Initial Investigations of Hops as a Salmonid Egg Fungicide

Abstract

Hatchery incubation of salmonid eggs typically requires the use of chemical fungicides that possess potential negative effects on human health or the environment. Strobiles from the hops Humulus lupulus plant have exhibited antimicrobial properties in nonaquaculture situations. This study investigated the use of hops as an alternative zoosporic fungal treatment with three experiments. In the first experiment, dried strobiles from wild variety hops were ground and placed at two concentrations in petri dishes containing sesame seeds and hatchery water containing Saprolegnia diclina. There was a positive relationship between the concentrations of hops and the amount of time elapsed before the observance of zoosporic fungal infestation. In subsequent experiments, the antimycotic activity of two concentrations of commercially available Summit variety hop pellets were evaluated using dead Chinook salmon Oncorhynchus tshawytscha eggs in vertical-flow incubation trays. In the second experiment, which involved static treatments of either 24 or 48 g of hop pellets wrapped in cheesecloth, zoosporic fungi appeared on the eggs in all the treatments at the same time and developed at the same rate. In the third experiment, the cheesecloth was eliminated and hop pellets were placed directly in the incubation trays at amounts of either 224 g for the entire duration of the experiment, or 112 g initially with 88 g of hops added after 3 d. Zoosporic fungi did not appear on the dead eggs in any of the hops treatment trays until 72 h after water mold was observed on the controls. Hops also delayed complete egg infestation by 72 h. Results from these experiments indicate for the first time the potential use of both wild and commercially available hops to control zoosporic fungi on incubating salmonid eggs.

Received October 3, 2011; accepted November 25, 2011

ACKNOWLEDGMENTS

We thank Mindy Capp, Tom Mead, and Darlene Thompson for their assistance with this study.