Correlation of five essential elements in the three tissues of crayfish
The concentrations of five essential elements (Mn, Fe, Cu, Zn and Se) in the red swamp crayfish were examined and the results showed the wide variations for the concentration of the trace of Mn, Fe, Cu and Zn among the tissues of haptopancreas, abdominal muscle and exoskeleton (Table 1). The concentration of Mn in abdominal muscle was 21.02 mg kg− 1, significantly lower than those of in haptopancreas (236.07 mg kg− 1) and exoskeleton (274.67 mg kg− 1). The concentration of Fe (2517.94 mg kg− 1) in haptopancreas was highest, followed by that in exoskeleton (114.92 mg kg− 1), and the one in abdominal muscle (34.85 mg kg− 1) was lowest. The mean concentration of Cu, Zn and Se was highest in haptopancreas, medium in abdominal and lowest in exoskeleton (Table 1). The variation coefficient of the concentration of the five essential elements in the three tissues was arranged from 0.10 to 2.42 (Table 1). For the elements of Se and Fe, there is a highly significant association among muscle, hepatopancreas and exoskeleton (P < 0.01) (Supplementary table 1). The content of Mn in exoskeleton has the significant positive relevance with that of in muscle and hepatopancreas (P < 0.01). The content of Cu between exoskeleton and muscle has the significantly positive correlation and the content of Zn between muscle and hepatopancreas has the significantly positive correlation (P < 0.01).
Table 1
The concentrations of five essential elements in the different tissues of red swamp crayfish (Procambarus clarkii) (mg kg− 1, Dry weight)
Element
|
Am
|
He
|
Ex
|
Mn
|
21.02 ± 17.77b
|
236.07 ± 191.75a
|
274.67 ± 236.98a
|
CV
|
0.85
|
0.81
|
0.86
|
Fe
|
34.85 ± 17.72c
|
2517.94 ± 1571.74a
|
114.92 ± 108.81b
|
CV
|
0.51
|
0.62
|
0.95
|
Cu
|
19.62 ± 7.93b
|
116.85 ± 283.34a
|
16.52 ± 8.76c
|
CV
|
0.40
|
2.42
|
0.53
|
Zn
|
73.95 ± 7.72b
|
124.74 ± 60.43a
|
21.79 ± 8.55c
|
CV
|
0.10
|
0.48
|
0.39
|
Se
|
1.04 ± 0.47b
|
2.56 ± 0.89a
|
0.38 ± 0.16c
|
CV
|
0.45
|
0.35
|
0.42
|
Data were showed with mean ± SD; He, hepatopancreas, Am, abdominal muscle, Ex, exoskeleton; a, b and c, ranked by Duncan test at P < 0.05. |
As shown in Supplementary table 2 and Supplementary table 3, the content of Mn in crayfish has a significant positive association with Cu (P < 0.01), Zn (P < 0.05) and Se (P < 0.01) in hepatopancreas, has a highly significant positive correlation with Cu, Zn and Fe (P < 0.01) in muscle, also has a highly significant positive correlation with Cu and Fe in exoskeleton (P < 0.01), but has a significant negative correlation with Zn in exoskeleton (P < 0.05). The content of Se both in heptopancreas and exoskeleton of crayfish has a highly significant positive correlation with Zn (P < 0.01). The content of Se have a highly significant positive correlation with Cu in exoskeleton (P < 0.01), and Fe in hepatopancreas (P < 0.01).
Correlation of the five essential elements between crayfish and environment
The significant difference for the five essential concentrations in each of the three tissues were examined among the four investigated geographic regions (Fig. 2, Supplementary Fig. 1 and Supplementary Fig. 2). Three of the five elements (Mn, Fe and Zn) in abdominal muscle showed the highest content in the region of northwest of Poyang Lake (NWPYL) where had the highest concentration of the five elements in haptopancreas among the four investigated regions. On the contrary, the concentrations of three elements including Mn, Zn and Se both in abdominal muscle and haptopancreas were lowest in the region of north of Dongting Lake (NDTL). But the concentration of Cu for three tissues was lowest in the region of south of Dongting Lake (SDTL). The concentrations of Se in two tissues of abdominal muscle and exoskeleton were the highest in the Enshi region (ESR) (Fig. 2 and Supplementary Fig. 2).
There was a highly significant positive correlation for the concentration of Se between sediment and abdominal muscle (r = 0.68) and exoskeleton (r = 0.72), respectively. A significant positive correlation was examined for the concentration of Cu between hepatopancreas and sediment (Table 2). The positive correlations were also identified for the concentration of Mn, Fe and Zn among abdominal muscle and sediments (0.14 ≤ r ≤ 0.34). Whereas, the negative correlations were examined for the concentration of Fe, Cu and Zn among exoskeleton and sediment (-0.43 ≤ r ≤ -0.17).
Table 2
The correlation of five essential elements concentrations between tissues and sediments.
Element
|
Mn
|
Fe
|
Cu
|
Zn
|
Se
|
Am
|
0.29
|
0.14
|
-0.09
|
0.34
|
0.68**
|
He
|
0.30
|
0.20
|
0.88**
|
0.27
|
0.28
|
Ex
|
0.34
|
-0.43
|
-0.17
|
-0.20
|
0.72**
|
He, hepatopancreas, Am, abdominal muscle, Ex, exoskeleton; “**”, represents P < 0.01. |
Different enrichment level for the five essential elements in red swamp crayfish
To investigate the element distribution of the different sample environments, the sediments and culture water of sixteen sample locations were examined the five elements. In sediment, the concentration of Fe, Mn, Cu, Zn and Se was arranged from 20.46 mg g− 1(Hujiawan) to 86.34 mg g− 1 (Liyushan), 79.91 mg kg− 1 (Taolin) to 751.36 mg kg− 1 (Chunmuying), 9.77 mg kg− 1 (Futian) to 139.72 mg kg− 1 (Liyushan), 27.20 mg kg− 1 (Futian) to 146.02 mg kg− 1 (Liyushan) and 0.11 mg kg− 1 (Chetianping) to 0.68 mg kg− 1 (Chunmuying), respectively (Supplementary table 4). The concentrations of the five elements in cultural water were far less than those of the sediment (data not shown). The bioaccumulation factors (BAF) of the five elements in crayfish were calculated, respectively. Three elements (Se, Zn and Cu) have been showed a high accumulation level in haptopancreas (BAF value more than 1) (Table 3). Interestingly, the accumulation level of Se elements was far more than those of the other four elements, the highest BAF value in haptopancreas was up to 17.65 (Table 3). Besides, the BAF values of the five elements in haptopancreas were higher than those in abdominal muscle. Furthermore, the similar accumulation situation was detected in the four investigated regions (Table 3).
Table 3
The bioaccumulation factor (BAF) values of five essential elements in haptopancreas and abdominal muscle to sediments
Region
|
Mn
|
Fe
|
Cu
|
Zn
|
Se
|
Am
|
H
|
M
|
H
|
M
|
H
|
M
|
H
|
M
|
H
|
SDTL
|
0.13
|
0.75
|
0.00
|
0.13
|
0.69
|
2.12
|
1.11
|
2.00
|
6.66
|
17.65
|
NWPYL
|
0.08
|
0.80
|
0.00
|
0.16
|
0.66
|
4.40
|
1.21
|
2.16
|
4.77
|
13.35
|
NDTL
|
0.05
|
0.29
|
0.00
|
0.12
|
1.07
|
3.97
|
1.44
|
2.13
|
4.18
|
11.68
|
ESR
|
0.06
|
1.29
|
0.00
|
0.09
|
1.28
|
4.63
|
1.31
|
2.57
|
2.77
|
6.31
|
SDTL, represents South of Dongting Lake region; NDTL, represents North of Dongting Lake region; NWPYL, represents Northwest of Poyang Lake region; ESR, represents Enshi region; Am, abdominal muscle; He, hepatopancreas. |
The enrichment of the five essential elements in different aquatic species
To validate whether the accumulation level and pattern of the five elements is specific in crayfish, the concentrations of the five elements both in the three different freshwater animals (crayfish, P. clarkii, crab, E. sinensis and carp, H. nobilis) and the corresponding sediments were examined in the same ponds with three independent repeats. The concentrations of three elements including Mn, Fe and Cu in haptopancreas of crayfish were significant higher than those of crab and carp, but the concentrations of Mn and Cu in muscle of carp were significant lower than those of crayfish and crab (Table 4 and Supplementary table 5). The concentration of Zn for haptopancreas was highest in carp (189.27 mg kg− 1), and lowest in crayfish (77.50 mg kg− 1). On the contrary, the concentration of Zn for muscle was lowest in carp (27.58 mg kg− 1), but was the highest in crab (205.52 mg kg− 1) (Table 4). For element of Se, there was a significant higher concentration for liver (7.60 mg kg− 1) and muscle (1.16 mg kg− 1) of carp than those of crayfish (haptopancreas, 2.15 mg kg− 1, abdominal muscle, 0.74 mg kg− 1) and crab (haptopancreas, 2.48 mg kg− 1, muscle, 0.90 mg kg− 1) (Table 4 and Supplementary table 5), respectively. In addition, the accumulation level (BAF) and pattern of the five elements in liver / haptopancreas and muscle of the three freshwater animals were similar. The BAF values of Mn and Fe in the two tissues of three animals were respectively smaller than 0.40, but the BAF value of Se was more than 3.90 (Table 5). Especially, they were more than 11 in haptopancreas of the three animals. The BAF value of Cu in two tissues of carp was smaller than those in crayfish and crab. The similar situation was observed for BAF value of Zn in muscle of the three animals, but it was opposite situation in liver / haptopancreas (Table 5).
Table 4
The concentrations of five essential elements in different Specie’s muscle (mg kg− 1).
Specie
|
Mn
|
Fe
|
Cu
|
Zn
|
Se
|
Crayfish
|
24.37 ± 6.14a
|
93.06 ± 29.55a
|
31.76 ± 4.55b
|
84.31 ± 6.18b
|
0.74 ± 0.09b
|
Carp
|
3.66 ± 1.02b
|
46.49 ± 16.84c
|
1.57 ± 0.26c
|
27.58 ± 2.33c
|
1.16 ± 0.10a
|
Crab
|
27.16 ± 11.01a
|
61.61 ± 16.05b
|
64.60 ± 14.76a
|
205.52 ± 14.6a
|
0.90 ± 0.13b
|
Carp, Bighead carp (Hypophthalmichthys nobilis); Carb, Chinese Mitten crab (Eriocheir sinensis); Crayfish, red swamp crayfish (Procambarus clarkii); Data were showed with mean ± SD; a, b and c, ranked by Duncan test at P < 0.05. |
Table 5
The bioaccumulation factor (BAF) values of five essential elements in different tissues to sediments
Species
|
tissues
|
Mn
|
Fe
|
Cu
|
Zn
|
Se
|
Crayfish
Carp
Crab
|
Am
|
0.04
|
0.00
|
1.19
|
1.17
|
3.92
|
0.01
|
0.00
|
0.06
|
0.38
|
6.20
|
0.05
|
0.00
|
2.41
|
2.86
|
4.81
|
Crayfish
Carp
Crab
|
He
|
0.36
|
0.11
|
11.88
|
1.08
|
11.47
|
0.03
|
0.02
|
4.06
|
2.63
|
40.46
|
0.05
|
0.03
|
4.58
|
1.83
|
13.23
|
Carp, Bighead carp (Hypophthalmichthys nobilis); Carb, Chinese Mitten crab (Eriocheir sinensis); Am, abdominal muscle; He, hepatopancreas. |