U.S. Fish and Wildlife Service

Effects of a partial reuse aquaculture system (PRAS) on proximate composition and smoltification of brood year 2017 steelhead (Oncorhynchus mykiss) reared at Hagerman National Fish Hatchery

Annual Report 2018

July 23, 2018 By Ronald Twibell1, Katey Strailey, Ashley

Carr, Kelli Hawke and Richard Glenn

Abernathy Fish Technology Center 1440 Abernathy Creek Road Longview, Washington 98632

1Email address: ronald_twibell@fws.gov

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Introduction

The desire to reduce water consumption at Hagerman National Fish Hatchery (HNFH,

Hagerman, ID) has prompted an evaluation of a partial reuse aquaculture system (PRAS).

Reputed advantages of reuse aquaculture systems (RAS) compared with traditional rearing

systems are that the former are environmentally sustainable, require less water and land area, and

facilitate environmentally safe waste management (Summerfelt et al. 2004, Timmons and

Ebeling 2010). Due to different rearing conditions in raceways and various water reuse designs,

it is likely that fish physiology could be affected by rearing system. For example, Chinook

salmon (Oncorhynchus tshawytscha) exhibited gill epithelial hypertrophy that was thought to be

caused by reduced water quality in a PRAS system (Good et al. 2011). Although studies with

Chinook and Atlantic salmon (Salmo salar) suggest that PRAS systems can be utilized to rear

anadromous fish to the desired size (Summerfelt et al. 2009, Good et al. 2011), the effects of

such systems on smolt to adult survival have not been reported. Given the critical role of HNFH

in rearing steelhead (O. mykiss) for conservation and mitigation purposes, there is a paucity of

information regarding the effects of PRAS on factors of importance to salmonid enhancement

programs such as maturation rates, smoltification, tissue proximate composition, outmigration

and adult returns.

Whole body proximate composition can provide information on energy reserves of fish

reared in different culture systems. Differences in water flow between PRAS and traditional

raceways could influence exercise rates thereby altering tissue proximate composition and

energy reserves. Exercise has been shown to alter body energy stores including changing fatty

acid profiles (Kiessling et al. 2005) and decreasing tissue lipid levels (Jobling et al. 1993, Jarboe

and Grant 1996, Simpkins et al. 2003) since lipids are preferentially consumed to power

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continuous swimming (White and Li 1985, Lauff and Wood 1996). However, the lipid lowering

effects of exercise have not been observed in all studies (Davison 1997, Rasmussen et al. 2011,

Grisdale-Helland et al. 2013).

Fish body composition may also change during smoltification as stored lipid is utilized to

fuel the increased metabolism required for seawater adaptation (Sheridan et al. 1983). Declining

tissue lipid reflects its use as an energy source for various physiological adaptations that must

occur for successful seawater entry, including increased gill Na+, K+ ATPase (NKA) enzyme

activity (Woo et al. 1978, Sheridan et al. 1983). Gill NKA enzyme activity can be an indicator

of migratory preparedness as upregulation of this enzyme is required for extrusion of salt to

maintain osmotic balance upon entering saltwater (Hoar 1988, Evans et al. 2005). Sheridan et al.

(1983) reported steelhead lipid levels began to decline in January and continued to do so until the

fish smolted in April while gill NKA enzyme activity increased in these fish during the same

period. As such, determination of tissue lipid content and gill NKA enzyme activity in fish

sampled during the months preceding hatchery release may be useful in evaluating the effects of

rearing system on steelhead smoltification at HNFH.

Objective

The objective of this project was to determine whether whole body lipid concentration

and gill NKA enzyme activity differed between brood year (BY) 2017 HNFH steelhead reared in

a PRAS or raceways.

Materials and Methods

Sample collection and analyses

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During the final three months of rearing at HNFH prior to release (January-March, 2018),

we randomly selected BY2017 steelhead for the determination of gill NKA enzyme activity and

whole body lipid level (Table 1). Twenty randomly selected fish were sampled each month from

each of three replicate PRAS tanks and seven raceways (Table 1). At the time of distribution,

mean density index (DI) of the rearing units that were sampled was 0.21, 0.20 and 0.19 for the

PRAS tanks (n=3), standard density raceways (SDR, n=3) and low density raceways (LDR,

n=4), respectively (Table 1). Fish in the LDR were stocked at a DI similar to that of the PRAS

tanks whereas the SDR were stocked at a density that was similar to the typical stocking density

used at HNFH. Weight and fork length (FL) of the 20 fish per replicate were measured prior to

gill sampling. Gill samples were excised according to McCormick et al. (1993) and transported

in liquid nitrogen to Abernathy Fish Technology Center (AFTC). At AFTC, samples were stored

at -80°C until analyzed for NKA enzyme activity following the methods described in

McCormick (1993). Following gill biopsy, fish were euthanized and transported on ice to AFTC

where they were stored frozen (-20°C) until analyzed for whole body lipid level following

standard procedures (Folch et al. 1957). Samples of the final feeds fed to the fish in the PRAS

and raceways were analyzed for proximate composition according to standard procedures

(AOAC 2010).

Statistical analyses

Proportional data (whole body lipid concentration) were normalized using arcsine square

root transformation prior to statistical analysis. Data from each sampling date were analyzed

separately by one-way analysis of variance (ANOVA) using the statistical package R (R Core

Team, 2015) with an accepted level of statistical significance of 0.05. If a significant difference

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was detected by ANOVA, Tukey’s honestly significant difference test was used to compare

treatment means.

Results

Rearing system had little effect on the responses analyzed in the current evaluation

(Table 1). On 1/09/18 and 2/13/18 condition factor was significantly lower in LDR steelhead

compared with PRAS steelhead. No other significant differences were detected during the three

sample dates (Table 1). Of the two final diets fed to the steelhead prior to release, lipid content

was somewhat higher in the diet fed to the raceway fish compared to the diet fed to the PRAS

fish (Table 2).

Discussion

The present results for BY2017 HNFH steelhead are in agreement with the findings for

BY2016 HNFH steelhead (Twibell et al 2017) that suggest a PRAS can be utilized to produce

steelhead that, at hatchery release, do not differ in size, body composition or in gross smolting

characteristics compared with steelhead produced in conventional raceways. Although slight but

statistically significant differences in condition factor were detected in BY2017 steelhead

sampled in January and February, it is unlikely that such differences would have a meaningful

biological impact on post-release survival given that none of the other measured responses were

affected by rearing system and no differences were detected during the final sampling in March.

In our evaluation of BY2016 HNFH steelhead, PRAS fish were smaller and leaner than raceway

fish in January and February, but not at the final sampling in March (Twibell et al. 2017).

Differences in size, condition factor and body composition among rearing systems during these

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two years could have resulted from a number of factors that varied between rearing systems,

including feed type, feed consumption, exercise and water quality. For example, the feeds fed to

BY2016 and BY2017 steelhead were produced by different manufacturers (Rangen, Inc. and

Skretting USA, respectively) and, in both years, the feed types fed to steelhead in the PRAS

(sinking pellets) and raceways (floating pellets) were somewhat different.

During smoltification, fish have an increased metabolic rate and consume lipid reserves,

ultimately becoming more slender than non-migratory parr (Folmar and Dickhoff 1980, Hoar

1988, Sheridan et al. 1983, Sheridan 1989, Sheridan and Kao 1998) which is reflected in reduced

condition factor (Hanson et al. 2011). This pattern of declining lipid level and condition factor

was evident in the PRAS and raceway fish, as both responses were lower in March compared

with the previous two months. However, steelhead in neither rearing system exhibited

increasing gill NKA enzyme activity during the months preceding downstream migration as has

been reported in other research with this species (Sheridan et al. 1983). There also was no

increase in the activity of this enzyme in BY2016 HNFH steelhead (Twibell et al. 2017). This

could reflect the great distance that steelhead reared in ID must travel to the ocean and the

possibility that gill NKA enzyme activity does not increase prior to hatchery release in these fish.

However, Samson et al. (1999) reported increasing gill NKA enzyme activity from February

through April in steelhead reared at Dworshak NFH near Orofino, ID. More research is needed

to determine when steelhead at HNFH exhibit signs of smoltification and whether gill NKA

enzyme activity is the most appropriate indicator of seawater preparedness in this stock of fish.

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Conclusions

Results of the BY2016 and BY2017 HNFH steelhead evaluations suggest that a PRAS

can be utilized to produce steelhead that, at hatchery release, do not differ in size, lipid level or

gross smolting characteristics compared with steelhead produced in conventional raceways.

However, information on downstream migration and survival to adult return is required to

determine the true impact of the PRAS system on the conservation and mitigation efforts of the

hatchery.

Data management

A copy of the report is archived in the AFTC database and can be made available to the

public upon request.

Acknowledgements

Funding for this project was provided by the U.S. Fish and Wildlife Service, Lower

Snake River Compensation Plan. Assistance with sample collection provided by HNFH staff is

gratefully acknowledged. The findings and conclusions in this report are those of the authors

and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

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Table 1. Mean weight, fork length, condition factor, gill Na+, K+-ATPase (NKA) enzyme activity and whole body lipid concentration

of steelhead reared in a partial reuse aquaculture system (PRAS) or raceways at Hagerman National Fish Hatchery.1

____________________________________________________________________________________________________________

Date

Rearing Unit

Density Index2

Weight

Fork

Length

Condition

Factor4

Gill NKA

Activity5

Whole Body

Lipid

(g) (mm) (%)

____________________________________________________________________________________________________________

1/09/18 PRAS Tanks 0.21 61.1 174 1.14a 1.2 7.5

Low Density Raceways 0.19

62.3 178 1.09b 1.2 8.0

Standard Density Raceways 0.20

58.3 173 1.11ab 1.2 7.6

Probability3 0.325 0.188 0.0051 0.956 0.159

2/13/18 PRAS Tanks 0.21

91.2 198 1.13a 0.9 7.6

Low Density Raceways 0.19

83.5 198 1.06b 0.8 7.6

Standard Density Raceways 0.20 80.5 194 1.08ab 0.9 8.0

Probability 0.095 0.352 0.021 0.296 0.359

3/27/18 PRAS Tanks 0.21

118.6 219 1.09 0.6 6.6

Low Density Raceways 0.19

118.0 221 1.07 0.6 7.3

Standard Density Raceways 0.20

108.0 216 1.05 0.7 7.3

Probability 0.215 0.486 0.322 0.726 0.098

1At each sampling date, means in the same column with different letters are significantly different (P < 0.05).

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Table 1 continued.

2Density index (total weight of fish/(mean fish length x rearing volume)) at distribution. Fish distribution occurred from April 2-6,

2018.

3Probability of treatment differences as determined by ANOVA.

4Condition factor was calculated as: (weight/fork length3) .100000.

5Units: µmol ADP.mg protein-1.h-1.

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Table 2. Analyzed proximate composition of final feeds fed to steelhead reared in a

partial reuse aquaculture system (PRAS) or raceways prior to release from Hagerman

National Fish Hatchery.

________________________________________________________________________

Diet Protein Lipid Moisture Ash

(%) (%) (%) (%)

________________________________________________________________________

Skretting USA Floating

Steelhead Diet, 4.5 mm, lots

4616799/4553191/46506981

46.2 19.1 7.9 8.3

Skretting USA Sinking

Steelhead Diet, 4.0 mm, lot

42724522

46.2 16.2 9.2

8.6

1Diet fed to steelhead reared in raceways.

2Diet fed to steelhead reared in PRAS.

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U.S. Fish & Wildlife Service Abernathy Fish Technology Center Longview, Washington, 98632 Phone: 360-425-6072 https://www.fws.gov/aftc/