Attempts to Improve Survivorship and Condition of Pond‐Reared Hybrid Striped Bass during Live Transport

Abstract

Anecdotal information from fish growers in Illinois has suggested that pond‐reared hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis) are more vulnerable to transportation‐related stressors than are cage‐reared fish. We conducted two simulated transport experiments to verify these reports and explored ameliorative strategies. In experiment 1, we evaluated changes in blood chemistry and water quality during transport of pond‐ versus cage‐reared hybrid Striped Bass. Replicate trials were conducted on 4 d in August 2013. For each trial, market‐size fish (weight = 650 ± 13 g, mean ± SE) were harvested from earthen ponds and floating cages, stocked in a two‐compartment, semibaffled, insulated, aluminum live hauler supplied with supplemental oxygenation (density = 97 ± 3 g/L), and held for 8 h. Changes in circulating cortisol, glucose, lactate, and osmolality indicated all fish underwent an acute stress response following harvest and transport, but subtle differences in performance and conditions experienced by pond‐ versus cage‐reared fish suggested greater CO2 accumulation during transport of pond‐reared fish may be problematic. Accordingly, in experiment 2, we evaluated changes in blood chemistry and water quality occurring during transport of pond‐reared hybrid Striped Bass with or without agitation. The same hauler was fitted with “bull‐style” agitators and stocked with market‐size, pond‐reared fish (weight = 812 ± 12 g, density = 106 ± 3 g/L), and replicate trials were conducted on 4 d in April–May 2014 in a manner otherwise identical to experiment 1. Although agitation mitigated CO2 accumulation and stabilized pH, total ammonia nitrogen equilibrium shifted in favor of un‐ionized ammonia nitrogen. Minor differences in blood chemistry were noted, but the use of agitators did not substantially attenuate the stress response observed. Harvest may be a greater stressor than others experienced during transport, and seining may contribute to poorer condition of pond‐reared fish during and after transport.