Evaluation of Barley Straw and a Commercial Probiotic for Controlling <i>Prymnesium parvum</i> in Fish Production Ponds

Abstract

Abstract Since 2001, the ichthyotoxic microalga Prymnesium parvum has caused major fish kills in 13 U.S. states, including Texas, raising concerns about its impacts on hatchery fish production, sport fisheries, and local economies. We investigated the efficacy of two natural products, barley Hordeum vulgare straw and the probiotic Liquid Live Micro-Organisms (LLMO) System in controlling P. parvum and its ichthyotoxicity. Their effects on factors essential for successful production of fingerling fish (i.e., water quality, nutrient levels, phytoplankton biomass and composition, zooplankton density and composition, and fingerling fish production) were also evaluated. Barley straw and LLMO were individually tested during summer and fall 2004 in hatchery ponds for 140 d (experiment 1). Four ponds were treated with barley straw applied once at the beginning of the study at 252 kg/ha, and four ponds received LLMO at a rate of 1 L/56,718 L of pond water at 2-week intervals throughout the study. Another four ponds were untreated and served as the control. Barley straw was further tested at 280 kg/ha in winter 2005 for 93 d (experiment 2). These barley straw treatment rates were similar to those used in other studies, and the LLMO rate was recommended by the supplier. In both experiments, P. parvum blooms did occur. Neither barley straw nor LLMO had a significant effect on P. parvum density, toxin levels, or ichthyotoxicity at the rates used in this study. Similarly, neither barley straw nor LLMO affected any of the other variables investigated. Our results do not support reports that barley straw and LLMO can control planktonic algae.