TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

filtered through 90 μm openings within a rotating drum filter (Model RFM 3236, PRA
Manufacturing Ltd., Nanaimo, British Columbia, Canada) before it enters a pump sump
(Figure 1). Other than a small water overflow from the pump sump, the majority of water
is pumped by one, two, or three 1.5-hp centrifugal pumps (Model B2-½TPMS, Berkley
Pumps, Delevan, Wisconsin) through an packed aeration column (Figure 1). The water
exiting the aeration column then gravity flows back to the culture tanks after first passing
through a low head oxygenator (Model MS-LHO-400 gal/min, aluminum construction,
PRA Manufacturing Ltd.) installed within a cone-bottom sump (Figure 1). The system
water’s pH was controlled by adjusting the amount of carbon dioxide stripped by turning
the fan “on” and “off.” Initially, fan control was manual, but later a pH controller (GLI
International, Milwaukee, Wisconsin) was used.
Fish and Feeding
The partial-reuse system was stocked with 36,943 15-gram rainbow trout. Fish were fed a
High Fat Trout Grower diet (Zeigler Brothers, Gardner, PA) that contained approximately
38% crude protein and 12% crude fat. Fish were first hand fed to satiation and later fed
to satiation using a commercial ultrasonic waste feed controller that was developed by
Culture Tools, Inc. (Monkton, VT), as described by Tsukuda et al. (2000). Records were
kept on the number of 22.7 kg (50 lb) feed bags fed daily (e.g., 0, 1, or 2 bags per tank per
day) and then these numbers were summed to provide a weekly total feed consumption.
Dead fish were removed daily and weak-appearing trout were culled daily. Records were
kept on the number of culled and dead fish removed. Mean fish size was estimated
bimonthly by weighing in bulk around 300 fish from each tank. Feed conversion rates
were calculated from the total mass of feed fed divided by the total mass of fish produced.
No chemical or antibiotic treatments were used during this study. The experimental
protocol and the methods described were in compliance with the Animal Welfare Act
(9CFR) requirements and were approved by the Freshwater Institute Institutional Animal
Care and Use Committee.
Water Quality Determination
Dissolved oxygen, pH, temperature and flow probes were used to continuously monitor
water quality and quantity within the system. Additionally, water samples were collected
three times weekly (typically) to quantify the concentrations of total ammonia-nitrogen,
nitrite-nitrogen, nitrate-nitrogen, dissolved carbon dioxide, pH, alkalinity, and total
suspended solids, at several locations within the system.
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