Sudden increased mortality in large seemingly healthy farmed Atlantic salmon (Salmo salar L.) was associated with environmental and dietary changes

Figures & data

Figure 1. The weighted mean dietary lipid (a) and protein level (b) of the control and test experimental diet series used during the production cycle (May 2015 to July 2016). The values for protein and lipid levels are based on the mean Near Infrared (NIR) analysis of each batch, weighted for the total amount of feed produced in each batch of the particular pellet size

Figure 2. Ambient daily sea temperature (°C, y-axis), day length (hours of daylight, z-axis) (a) and weekly cumulative mortality during the production cycle for the control and test pens (b) during the production cycle (May 2015 to July 2016). The specific feeding rate (%) for the control and test pens from December 2015 to May 2016 (c)

Table 1. Fatty acid composition (% of total) of the 10 mm winter test and control diets used prior to the increased mortality among the test group

10 mm winter diet	Control	Test
14:0	1.9	2.4
16:0	7.9	8.0
18:0	2.6	2.2
Σ SFA^a	14.0	14.0
16:1n-7	1.6	1.9
18:1n-9	40.0	38.0
18:1n-7	5.4	4.6
20:1n-9	2.9	3.8
Σ MUFA^b	52.8	52.2
18:2n-6	16.3	14.0
20:4n-6	0.2	0.2
Σ n-6^c	16.8	14.7
18:3n-3	5.8	5.9
20:5n-3	4.4	5.5
22:5n-3	0.4	0.6
22:6n-3	2.6	3.5
Σ n-3^d	13.5	15.7
n-3/n-6	0.8	1.1

^aIncludes 15:0, 17:0, 20:0, 22:0, and 24:0.

^bIncludes 14:1n-5, 16:1n-5, 17:1n-7, 22:1n-7, 22:1n-11, 22:1n-9, and 24:1 n-9.

^cIncludes 16:2n-6, 18:3n-6, and 20:2n-6.

^dIncludes 16:2n-3 and 20:4n-3.

Figure 3. Percentage change of muscle fat content during the experimental period (May 2015 – June 2016) for the control and test group. Samplings were conducted in May, June, and October 2015, in addition to January and June 2016. Values are shown as pooled means of the pens

Figure 4. Visceral somatic index (a) and visceral fat score (b) of Atlantic salmon fed control and test dietary series sampled January 7, 2016. Values are shown as pen means ± SEM, n = 10

Table 2. Biometric data of Atlantic salmon fed the two experimental diets and presenting differences in health status. (Mean values with their standard errors; n = 10)

Dietary treatment	Control	Test	Test	P-value
Health status	Normal	Normal	Moribund	Diet	Health status
Body weight, g	2533 ± 227	2501 ± 152	2511 ± 151	ns	ns
Gutted weight, g	2201 ± 192	2211 ± 129	2145 ± 104	ns	ns
Length, cm	57.6 ± 1.6	58.3 ± 1.0	57.6 ± 1.0	ns	ns
CF	1.30 ± 0.04	1.25 ± 0.03	1.31 ± 0.04	ns	ns
CFg	1.13 ± 0.03	1.11 ± 0.02	1.12 ± 0.02	ns	ns
HSI	1.49 ± 0.08	1.48 ± 0.05	1.56 ± 0.09	ns	ns
Liver score, 0 – 5	1.7 ± 0.1	2.3 ± 0.3	1.3 ± 0.2	ns	0.001

CF; condition factor, CFg; condition factor gutted, HSI: hepatic-somatic index.

Table 3. Fatty acid composition (% of total) in the liver of Atlantic salmon fed the two experimental diets and presenting differences in health status. (Mean values with their standard errors; n = 10)

Dietary treatment	Control	Test	Test	P-value
Health status	Normal	Normal	Moribund	Diet	Health status
14:0	1.0 ± 0.12	1.2 ± 0.14	1.4 ± 0.03	ns	ns
16:0	7.7 ± 0.30	7.3 ± 0.19	6.6 ± 0.29	ns	ns
18:0	3.9 ± 0.14	3.7 ± 0.09	3.5 ± 0.15	ns	ns
Σ SFA^a	13.4 ± 0.31	13.0 ± 0.25	12.4 ± 0.39	ns	ns
16:1n-9	0.0 ± 0.00	0.1 ± 0.04	0.1 ± 0.05	0.025	ns
16:1n-7	1.7 ± 0.07	1.9 ± 0.13	2.4 ± 0.13	ns	0.001
18:1n-9	36.0 ± 0.97	35.8 ± 1.65	40.6 ± 0.92	ns	0.001
18:1n-7	2.8 ± 0.04	2.9 ± 0.09	3.2 ± 0.06	ns	0.009
20:1n-9	4.7 ± 0.13	4.7 ± 0.13	5.0 ± 0.20	ns	ns
Σ MUFA^b	48.5 ± 1.23	49.1 ± 1.66	54.9 ± 1.24	ns	0.006
18:2n-6	10.5 ± 0.21	9.5 ± 0.33	9.8 ± 0.23	0.023	ns
20:4n-6	0.8 ± 0.08	0.9 ± 0.09	0.6 ± 0.04	ns	0.027
Σ n-6^c	11.4 ± 0.18	11.3 ± 0.25	10.6 ± 0.21	ns	0.051
18:3n-3	3.2 ± 0.12	3.3 ± 0.10	3.4 ± 0.08	ns	ns
18:4n-3	2.0 ± 0.05	1.6 ± 0.23	1.9 ± 0.05	ns	ns
20:5n-3	4.9 ± 0.32	4.1 ± 0.30	3.0 ± 0.17	0.031	0.010
22:5n-3	1.4 ± 0.08	1.5 ± 0.16	1.1 ± 0.09	ns	0.023
22:6n-3	11.1 ± 0.71	12.2 ± 1.46	8.2 ± 0.71	ns	0.011
Σ n-3^d	23.6 ± 1.02	23.6 ± 1.74	18.9 ± 0.93	ns	0.02
∆^9 DI^e	3.3 ± 0.18	3.5 ± 0.21	4.3 ± 0.24	ns	0.008

^aIncludes 15:0, 17:0, 20:0, 22:0, and 24:0.

^bIncludes 14:1n-5, 16:1n-5, 17:1n-7, 20:1n-11, 22:1n-7, 22:1n-11, 22:1n-9 and 24:1 n-9.

^cIncludes 16:2n-6, 18:3n-6, 20:2n-6, and 20:3n-6.

^dIncludes 16:2n-3, 20:4n-3, and 20:3n-3.

^e∆⁹ DI = (16:1n-7 + 18:1n-9)/(16:0 + 18:0)

Figure 5. Liver fat content of Atlantic salmon sampled February 3, 2016. Normal-C; normal fish from control pens, Normal-T; normal fish from the test pens, Moribund-T; diseased/moribund fish from the test pens. Values are shown as means ± SEM, n = 10. Significant differences (P < .05) are indicated by different subscript letters on the bars

Figure 6. Alanine aminotransferase (a) and alkaline phosphatase (b) and aspartate aminotransferase (c) in plasma of Atlantic salmon sampled February 17, 2016. Normal-C; normal fish from control pens, Normal-T; normal fish from the test pens, Moribund-T; diseased/moribund fish from the test pens. Values are shown as means ± SEM, n = 10. Significant differences are indicated over the bars

Figure 7. Daily mortality in test-pens 2 and 3 from starvation February 15 and until the end of March 2016. Feeding was resumed on March 12, 2016