Effects of stunning methods on pre rigor changes in rainbow trout (Oncorhynchus mykiss) reared at two different temperatures

Figures & data

Table 1. Blood plasma parameters and cortisol levels in rainbow trout reared at 8 °C or 12 °C and stunned by asphyxia with CO (CO) or electricity (E) (n = 5 fish/experimental group).

	Stunning (S)		Temperature (T)		Significance			RSD
	CO	E	8 °C	12 °C	S	T	S × T
Glucose, mM	7.46	5.00	5.99	6.48	***	ns	ns	0.74
Lactate, mM	5.33	3.26	3.94	4.65	***	*	ns	0.73
Cortisol, ng/mL	38.60	62.30	46.60	54.30	ns	ns	ns	52.10
K^+, mM	6.62	6.04	7.40	5.25	ns	*	**	0.66

*p < .05; **p < .01; ***p < .001; ns: not significant; RSD: residual standard deviation.

Table 2. Results of the significant interaction (stunning × temperature, S × T) emerged for K⁺ (mM) plasma content.

	Stunning
	CO	E
Temperature
8 °C	8.12^A	6.69^B
12 °C	5.11^C	5.40^C

A,B,C: means with different superscripts are significantly different at p ≤ .01 level.

CO: carbon monoxide asphyxia; E: electroshock.

Table 3. ATP contents, AEC values, and fillets shape changes immediately post mortem in muscle of rainbow trout reared at 8 °C or 12 °C and stunned/slaughtered by asphyxia with CO (CO) or electricity (E) (n = 3 fish/experimental group).

	Stunning (S)		Temperature (T)		Significance			RSD
	CO	E	8 °C	12 °C	S	T	S × T
Energy content
ATP, µmol/g	2.28	1.12	1.05	2.35	*	*	ns	0.85
AEC	0.83	0.64	0.61	0.85	***	***	*	0.05
Fillet shape
Perimeter, cm	60.98	59.11	60.05	60.04	ns	ns	ns	2.18
Area, cm^2	141.24	134.26	138.76	137.75	**	ns	ns	3.68
Length, cm	24.57	23.93	24.43	24.07	ns	ns	ns	1.05
Width, cm	7.72	7.46	7.56	7.62	ns	ns	ns	1.69

*p < .05; **p < .01; ***p < .001; ns: not significant; RSD: residual standard deviation; CO: carbon monoxide asphyxia; E: electroshock; S × T: stunning × temperature; AEC: Adenylate Energy Charge; ATP: Adenosine triphosphate. .

Table 4. Results of the significant interaction (stunning × temperature, S × T) emerged for AEC values determined immediately post mortem (T0) in muscle of rainbow trout reared at 8 °C or 12 °C and stunned by asphyxia with CO (CO) or electricity (E).

	Stunning
	CO	E
Temperature
8 °C	0.81^A	0.42^B
12 °C	0.84^A	0.86^A

A,B: means with different superscripts are significantly different at p ≤ .01 level.

CO: carbon monoxide asphyxia; E: electroshock.

Figure 1. Post mortem evolution of rainbow trout pH as affected by rearing water temperature [8 °C, (A); 12 °C, (B)], and stunning methods (asphyxia with CO, CO; electricity, E). Values are presented as means (n = 5 fish/experimental group). Vertical bars indicate the standard deviation.

Figure 2. Post mortem evolution of rainbow trout Rigor Index (RI, %) as affected by rearing water temperature [8 °C, (A); 12 °C, (B)], and stunning methods (asphyxia with CO, CO; electricity, E). Values are presented as means (n = 5 fish/experimental group). Vertical bars indicate the standard deviation.

Figure 3. Effect of asphyxia with CO (CO) or electricity (E) stunning methods on perimeter, area, maximum length and maximum width in fillets of rainbow trout, measured at different times after death, expressed as percentage of the value measured immediately after death (n = 3 fish/experimental group).

Figure 4. Effect of rearing temperature (water set at 8 or 12 °C) on perimeter, area, maximum length and maximum width in fillets of rainbow trout, measured at different times after death, expressed as percentage of the value measured immediately after death (n = 3 fish/experimental group).