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Chinook raised in partial RAS outshine its raceway-grown counterparts

December 19, 2019
By Jean Ko Din


Catherine Willard presented her team’s findings at the Northwest Fish Culture Concepts Annual Meeting in Victoria, B.C.
VICTORIA, B.C. – Chinook salmon smolts reared in a partial reuse aquaculture system (PRAS) are outperforming their counterparts reared in traditional flow-through raceways in Washington State.

Senior fisheries biologist Catherine Willard from Chelan County Public Utility District led a presentation on the team’s findings at the 70th Northwest Fish Culture Concepts Annual Meeting and Workshops in Victoria, B.C., Canada. On Dec. 3, she shared the stage with Josh Murauskas of Four Peaks Environmental to share what they have learned in raising 500,001 summer Chinook yearling smolts at the Eastbank Fish Hatchery.

When they first started tracking the coded wire tags (CWT) and the passive integrated transponder (PIT) of the fish in PRAS and their “SUPER” raceways, Murauskas said the one question they wanted to answer is if the PRAS system was going to perform in the same way, if not better.

“Every single year, and not only in this program but in other programs we looked at, it’s a slam dunk,” he said.

Murauskas showed graphs that indicated PRAS fish that had consistently faster travel times downstream than the raceway fish. In five of the past seven years, PRAS fish have also seen better survival rates than their raceway counterparts. In the Chelan River, data showed a 20-percent increase in survival rates of juvenile summer Chinook.

Aside from the improved water conservation and quality, the shape of the vessels where the smolts were reared make a huge difference, said Willard. She said it’s as if the fish reared in the circular PRAS vessels are being raised on a full exercise program ¬– like on a treadmill as opposed to just sitting at your desk.

“We joke about treadmills and all these kinds of stuff but it’s about two to four body lengths per second that you’re seeing the fish in the reuse (PRAS),” added Murauskas. “And they’re also distributed a lot throughout the water column, as opposed to a raceway. In a raceway, it’s maybe about half a body length per second.”

Chelan Public Utility District’s (PUD) Eastbank Hatchery pumps its ground water from the Columbia-River-charged Eastbank Aquifer, which is shared with the regional water supply system. The Eastbank Aquifer provides water to businesses and residents within the greater Wenatchee Valley. Projecting increases in demand from the regional water supply system due to community growth, Chelan PUD evaluated options for water conservation at its Eastbank Hatchery.

The pilot program for the PRAS system was first implemented in 2008. They quickly realized the operational benefits of using identical flow and density indices that use only a quarter of the amount of water used in traditional flow-through raceways.

The water quality was also consistently better because of the consistent hydraulic flow that distributes the dissolved oxygen throughout the circular vessel. Willard said waste capture of suspended sediments in the water is also “emphatically improved.” Staff labor is significantly reduced because of the tanks’ self-cleaning attributes.

“It was just a pilot for just a few years,” said Ian Adams, hatchery maintenance and operations coordinator at Chelan PUD. “The intention was to actually just tear it down. It was so successful that we left it.”

Adams helped implement the PRAS system in which 120,000 summer Chinook are being early reared in. The other 380,000 smolt are reared in the “super” raceways. He said the advantage of a PRAS system, instead of a fully recirculating aquaculture system, is that there is a lot more risk involved in reusing 100 percent of the water.

“We’re bringing in roughly 20 percent of make-up water which is balanced with the appropriate alkalinity, the appropriate D.O. (dissolved oxygen), so we already have this guarantee of nice water coming in,” Adams explained to Hatchery International. “When you do 100 percent recirc, you’re relying on all that infrastructure to keep functioning to keep that water quality at the appropriate balance.”

Based on their findings at Chelan PUD, Willard said the PRAS system comes highly recommended.

“If you’re building a new hatchery, there is no other vessel. You should do circular vessels and if you can, do reuse because you use less water,” she said.

After completing 10 years of this program, Willard said Chelan PUD is looking to expand to its steelhead stock where they are seeing similar results in the PRAS and raceway systems. She said the team is also interested in diving deeper into the mechanisms that are contributing to the better performance of PRAS fish.

“We think it’s because they’re exercising but we don’t know for sure. That would be an interesting thing to figure out – what specifically is happening with the fish to make them perform better,” said Willard.

Aquacultural Engineering
Volume 31, Issues 3–4, October 2004, Pages 157-181
Aquacultural Engineering
A partial-reuse system for coldwater aquaculture
Author links open overlay panelSteven TSummerfeltJohn WDavidsonThomas BWaldropScott MTsukudaJulieBebak-Williams
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doi.org/10.1016/j.aquaeng.2004.03.005Get rights and content
Under a Creative Commons licenseopen access
Abstract
A model partial-reuse system is described that provides an alternative to salmonid production in serial-reuse raceway systems and has potential application in other fish-culture situations. The partial-reuse system contained three 10 m3 circular ‘Cornell-type’ dual-drain culture tanks. The side-wall discharge from the culture tanks was treated across a microscreen drum filter, then the water was pumped to the head of the system where dissolved carbon dioxide (CO2) stripping and pure oxygen (O2) supplementation took place before the water returned to the culture tanks. Dilution with make-up water controlled accumulations of total ammonia nitrogen (TAN). An automatic pH control system that modulated the stripping column fan ‘on’ and ‘off’ was used to limit the fractions of CO2 and unionized ammonia nitrogen (NH3N). The partial-reuse system was evaluated during the culture of eight separate cohorts of advanced fingerlings, i.e., Arctic char, rainbow trout, and an all female brook trout × Arctic char hybrid. The fish performed well, even under intensive conditions, which were indicated by dissolved O2 consumption across the culture tank that went as high as 13 mg/L and fish-culture densities that were often between 100 and 148 kg/m3. Over all cohorts, feed conversion rates ranged from 1.0 to 1.3, specific growth rates (SGR) ranged from 1.32 to 2.45% body weight per day, and thermal growth coefficients ranged from 0.00132 to 0.00218. The partial-reuse system maintained safe water quality in all cases except for the first cohort—when the stripping column fan failed. The ‘Cornell-type’ dual-drain tank was found to rapidly (within only 1–2 min) and gently concentrate and flush approximately 68–88% (79% overall average) of the TSS produced daily within only 12–18% of the tank’s total water flow. Mean TSS concentrations discharged through the three culture tanks’ bottom-center drains (average of 17.1 mg/L) was 8.7 times greater than the TSS concentration discharged through the three culture tanks’ side-wall drains (average of 2.2 mg/L). Overall, approximately 82% of the TSS produced in the partial-reuse system was captured in an off-line settling tank, which is better TSS removal than others have estimated for serial-reuse systems (approximately 25–50%). For the two cohorts of rainbow trout, the partial-reuse system sustained a production level of 35–45 kg per year of fish for every 1 L/min of make-up water, which is approximately six to seven times greater than the typical 6 kg per year of trout produced for every 1 L/min of water in Idaho serial-reuse raceway systems.

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Keywords
ReuseRecirculatingAquacultureArtic charRainbow trout
1. Introduction
Traditionally, coldwater species have been cultured in raceways that take advantage of large water supplies in locations where space is limited, as in the Idaho Snake River valley and the mountains of North Carolina. Making the most of a large water resource, water is often serially reused as it flows by gravity from raceway to raceway that are stair-stepped down a hillside. However, water quality deteriorates as it moves from one raceway to the next. Dissolved and particulate wastes accumulate in the water column. Settleable particulates accumulate along the raceway bottoms and within the quiescent zones at the end of each raceway. Capture of particulate wastes is relatively inefficient in a raceway system—due to the length of time the solids are within the raceways and the relatively low concentrations involved—with a net capture efficiency of only 25–51% of the total suspended solids (TSS) produced (Mudrak, 1981). In addition, managing particulate wastes within raceway systems and their quiescent zones can account for 25% of farm labor (IDEQ, 1998). More stringent water pollution control and water use permitting, as well as limited availability of large high-quality water resources, have recently increased interest in alternate fish culture system designs that can economically sustain, or even increase, fish production levels using less water and achieving better waste capture efficiencies. To this end, we designed and evaluated a partial-reuse system capable of supporting high production densities and significantly better overall particulate waste capture efficiencies, all on ≤20% of the flow typically required within a flow-through raceway culture system.

A partial-reuse system settles or filters particles from the flow exiting the culture tanks before pumping 80% or more of the flow back to the head of the system where dissolved carbon dioxide (CO2) stripping and pure oxygen (O2) supplementation take place before the water is reused. A partial-reuse system includes one or more culture tanks that are plumbed so that the reused water flow passes through the tanks in parallel, rather than in series as with traditional raceways. Circular tanks can have distinct advantages over raceways and earthen ponds when applied to partial-reuse systems, because the water injected into each circular tank will completely mix to create uniform water quality throughout the tank, e.g., eliminating large profiles in dissolved O2 that would occur in plug flow culture vessels. Also, water rotational velocities can be adjusted (by adjusting the orientation and nozzle size at the water inlet to the circular tank) to create more optimum levels for fish health and solids flushing (Skybakmoen, 1989, Tvinnereim and Skybakmoen, 1989, Timmons et al., 1998). Circular tanks can self clean as they rapidly concentrate and flush settleable solids through their bottom-center drain due to the ‘tea-cup’ solids transport mechanism produced by the primary rotating flow about the tank’s central axis. Circular fish-culture tanks can also be converted into a “swirl” separator where concentrated solids are removed within a relatively small flow stream leaving their bottom-drawing center drain while the majority of flow is discharged with relatively fewer solids through an elevated drain located in the center of the tank (Makinen et al., 1988, Eikebrokk and Ulgenes, 1993, Skybakmoen, 1993, Lunde et al., 1997, Twarowska et al., 1997) or an elevated drain located at the perimeter of the tank, i.e., a ‘Cornell-type’ dual-drain culture tank (Timmons et al., 1998, Summerfelt et al., 2000, Summerfelt et al., 2004, Davidson and Summerfelt, in press). Therefore, removing solids from circular tanks using a dual-drain system can potentially improve the economics and efficiency of solids removal, both within the fish water column and from the effluents of flow-through and water-reuse systems.

This paper describes a partial-reuse system that was designed and installed at the CFFI’s facilities near Shepherdstown, West Virginia, USA. This paper also describes the water quality, waste capture efficiency, and stock performance during the culture of eight sequential cohorts of advanced fingerling Arctic char and rainbow trout. Additionally, this paper provides estimates of the system’s fixed cost, the electrical power cost per kg of fish produced, and labor requirements to clean and maintain the model partial-reuse system. However, this paper does not attempt to address the economics of partial-reuse systems, which is beyond the scope of this work.

2. Materials and methods
2.1. Partial-reuse system
The CFFI’s partial-reuse system (Fig. 1) contains three circular ‘Cornell-type’ dual-drain culture tanks (plumbed in parallel), a drum filter, a pump sump, three pumps (plumbed in parallel), a cascade aeration column, a low head oxygenation unit, and a sump tank to support the low head oxygenation unit (LHO) and provide the water head to drive the water flow back into the culture tanks. This system does not include a biofilter. A pump control system, an O2 control system, and a pH control system were also included. Details of each component are provided below. The fixed cost of the model partial-reuse system are shown in Table 1.