The effect of flow on size, weight and lipid levels of overwintering channel catfish Ictalurus Punctatus. (Middle Mississippi River).

Method

The lab work took place in the laboratory of the Missouri Department of Conservation.

Channel catfish were collected from the middle Mississippi River (near Cape Girardeau,

Missouri) during late fall 2016 using a mini-Missouri bottom trawl using the same procedure as

Herzog et al. (2005). All channel catfish were captured and returned to the laboratory at the Big

Rivers and Wetlands field station. Six hundred fish were used in this study.

For the purpose of this study, twelve ponds have been utilized to investigate the effects of

flow on fish size, weight and lipid levels. Half of these ponds were utilized in such a way that

would simulate flow and currents in a typical river. In other words, fish in these ponds were

exposed to flow. The other ponds were used as a control group. That is, the fish in this group

were not exposed to flow.

The daily care for the lab fish was as follows. The care began by shutting off power to the

powerheads and pumps. The fish were fed approximately 1-2 spoonful of frozen bloodworms

and the fish were given 10-15 minutes to consume the food. After 10-15 minutes, water was

siphoned out, including any excess food. When siphoning was finished, all ponds were refilled

with treated water from storage tanks. After the ponds were refilled, the power was turned back

on. Water in the storage tanks was treated with 2 capfuls of a conditioner to the storage water to

prepare and stored for one day.

On the 15th day of each month, I took ten random samples from each pond and measured

the size, weight and lipid levels. One hundred and twenty fish were collected on the 15th day of

each month also, from twelve different sites on the Mississippi river, six of these sites were areas

of high flow whereas the other six sites showed no flow. All channel catfish were captured and

processed at the laboratory at the Big Rivers and Wetlands field station. All fish were stored at -

20°C.

Lipid extraction protocol

The lipid levels of fish were determined using the phosphovanillan assay (Van Handel,

1985). Prior to homogenization, frozen individual fish were chopped into small parts while still

frozen to minimize loss of tissue. The pieces were added to a glass tube and followed by. Each

specimen was allowed to thaw and was homogenized in 20 ml 1:1 Methanol:Chloroform.

For each sample, I took 50 µl aliquot from the chloroform layer of the homogenate and

added it to the bottom of a 2.0 ml micro-centrifuge tube and let the solution dry under a fume

hood. Once the sample was dry, 200 µl of con sulfuric acid was added and the sample was heated

at 100 C for 10 min. Once heated, the samples were transferred to a labeled glass tube and 3 ml

of phosphovanillin reagent was added and allowed to develop for 30 min. The absorbance was

measured at 525 nm in a Spectrophotometer (Beckman Coulter DU 700 Series UV/Vis

Spectrophotometers) and compared to a standard curve using 4.5, 7.2, 9.0, 10.8, 13.5, 14.4, 18.0

mg corn oil. Total lipids were calculated following the analysis.

Statistical analyses

A MANOVA model (proc glm in SAS, SAS/STAT Software, SAS Institute Inc., Cary, NC) was

used to determine whether there was any effect of flow of time (month), flow and the

environment (field vs. lab) on the size, mass and lipid levels of overwintering channel catfish.

Results

The MANOVA was significant for month (F=3.31, DFN=6, DFD= 208, p=0.0039), flow (F=6.94

DFN=3, DFD= 104, p=0.0003) and environment (F=22.54 DFN=3, DFD= 104, p=0.0001).

There was a significant effect of month, flow, environment and significant interactions

between month and environment on size of fish (Table 1). Fish sampled in lab were significantly

larger than fish collected in the field in January (p=0.0001) and February (p=0.0001) but not in

March (p=0.27; Figure 1). Fish collected from the field were significantly larger in March than

they were in January (p=0.0001) or February (p=0.0058). There was no effect of flow on fish

raised in the lab but fish collected in no flow areas in the wild were significantly longer than

those collected in areas with flow (Figure 2).

There was a significant effect of month, flow, environment and significant interactions between

month and environment on weight of fish (Table 2). Fish sampled in lab were significantly larger

than fish collected in the field in January (p=0.0015) and February (p=0.0001) but not in March

(p=0.27; Figure 3). Fish collected from the field were significantly larger in March than they

were in January (p=0.0001) or February (p=0.0058). There was no effect of flow on fish raised

in the lab but fish collected in no flow areas in the wild were significantly heavier than those

collected in areas with flow (Figure 2).

There was a significant effect of environment (p=0.0002; Table 3), and significant interactions

between flow and environment on lipid levels of fish (p=0.0006; Table 3). Fish in flow areas in

the lab had more lipids than those which were collected in flow areas from the river (Figure 5).

Fish collected in no flow areas in the wild had more lipids than those collected in areas with flow

(Figure 5).

Tables

Table 1: Results of the MANOVA for Size.

Source DF Type I SS Mean Square F Value Pr > F

Month 2 0.51867335 0.25933667 7.60 0.0008

Flow 1 0.54405107 0.54405107 15.93 0.0001

Eviron 1 2.36271110 2.36271110 69.20 <.0001

Month*Flow 2 0.01749202 0.00874601 0.26 0.7745

Month*Eviron 2 0.31802061 0.15901030 4.66 0.0115

Flow*Eviron 1 0.17052063 0.17052063 4.99 0.0275

Month*Flow*Eviron 2 0.01909608 0.00954804 0.28 0.7566

Table 2: Results of the MANOVA for weight.

Source DF Type I SS Mean Square F Value Pr > F

Month 2 2.30037663 1.15018832 6.94 0.0015

Flow 1 3.10984753 3.10984753 18.75 <.0001

Eviron 1 9.79069868 9.79069868 59.05 <.0001

Month*Flow 2 0.11657175 0.05828587 0.35 0.7044

Month*Eviron 2 1.72752998 0.86376499 5.21 0.0070

Flow*Eviron 1 0.61382178 0.61382178 3.70 0.0570

Month*Flow*Eviron 2 0.12187032 0.06093516 0.37 0.6934

Table 3: Results of the MANOVA for lipid.

Source DF Type I SS Mean Square F Value Pr > F

Month 2 0.30202250 0.15101125 0.18 0.8376

Flow 1 0.05925283 0.05925283 0.07 0.7923

Eviron 1 13.05156506 13.05156506 15.34 0.0002

Month*Flow 2 2.25402682 1.12701341 1.32 0.2702

Month*Eviron 2 0.42978397 0.21489199 0.25 0.7772

Flow*Eviron 1 10.77487097 10.77487097 12.67 0.0006

Month*Flow*Eviron 2 2.04496189 1.02248095 1.20 0.3046

Figures

Figure 1: Size (± SE) of fish sampled from lab (blue bars) and wild (orange bars) populations

from January (Jan), February (Feb), and March (Mar). Different letters indicate significant

differences based on a MANOVA and Tukey Honest Significant Difference Test.

0

20

40

60

80

100

120

Jan Feb Mar

Size

a a a

b b

a

Figure 2: Size (± SE) of fish sampled from lab and wild populations with no flow (blue bars)

and with flow (orange bars). Different letters indicate significant differences based on a

MANOVA and Tukey Honest Significant Difference Test.

0

20

40

60

80

100

120

Lab Wild

Size

a a b

c

Figure 3: Weight (± SE) of fish sampled from lab (blue bars) and wild (orange bars) populations

from January (Jan), February (Feb), and March (Mar). Different letters indicate significant

differences based on a MANOVA and Tukey Honest Significant Difference Test.

0

2

4

6

8

10

Jan Feb Mar

Weight

aa a a

bb

Figure 4: Weight (± SE) of fish sampled from lab and wild populations with no flow (blue bars)

and with flow (orange bars). Different letters indicate significant differences based on a

MANOVA and Tukey Honest Significant Difference Test.

0

2

4

6

8

10

Lab Wild

Weight

a,b a

b

c

Figure 5: Lipid (± SE) of fish sampled from lab and wild populations with no flow (blue bars)

and with flow (orange bars). Different letters indicate significant differences based on a

MANOVA and Tukey Honest Significant Difference Test.

0

50

100

150

200

250

Lab Wild

Lipid/ g Fish

a,b

a

b

c