Is humane slaughtering of rainbow trout achieved in conventional production chains in Germany? Results of a pilot field and laboratory study.

BACKGROUND: Rainbow trout, Oncorhynchus mykiss, is an important fish in European freshwater aquaculture. This industry sector is dominated by small family-owned enterprises located in rural areas. A large percentage of rainbow trout produced by these small enterprises is marketed directly and killed on demand and not processed in commercial processing plants. EU and national regulations stipulate that fish shall be stunned prior to killing and slaughter. The overall objective of this study was to monitor how stunning interventions were integrated into the production chains of German conventional trout aquaculture in order to safeguard animal welfare during stunning and killing. For this, the stunning and slaughtering processes were monitored on 18 rainbow trout farms in various German federal states. During the on-farm research, (i) the stunning success, (ii) injuries related to the stunning procedure, (iii) duration between stunning and killing, and (iv) visible responses at the time of slaughtering were assessed as welfare indicators. In addition, haematological and biochemical blood parameters were measured as indicators for physiological stress. Due to the fact that stunning interventions should induce a loss of consciousness in fish, in a laboratory study, it was examined whether the absence of the brainstem/ behavioural responses, opercular movements (OM) or eye-rolling reflex (vestibulo-ocular reflex, VOR) was correlated with the stage of insensibility. RESULTS: The majority of rainbow trout farms applied manual percussion (38%) or electrical stunning (48%), while on 14% of the farms, the fish were stunned by electrical stunning which was immediately followed by manual percussion. After percussive stunning, about 92.3% of the rainbow trout displayed no OM or VOR as brainstem/ behavioural indicators of consciousness. This percentage varied on farms which applied electrical stunning. While on the majority of farms, 95 to 100% of the fish were unconscious according to the observation of brainstem/ behavioural indicators, the stunning intervention was less effective on farms where rainbow trout were stunned at current densities below 0.1 A dm2 or for a few seconds only. The laboratory study confirmed that the absence of brainstem/ behavioural indicators correlated with the absence of visually evoked responses (VER) of the brain to light stimuli as a neuronal indicator of insensibility. Therefore, the brainstem/ behavioural signs can be used to interpret the stage of insensibility in rainbow trout. A stage of insensibility could safely be induced by exposing portion-sized rainbow trout to an electric current density above 0.1 A dm2. This was not influenced by the orientation of the electric field. CONCLUSIONS: In conventional aquaculture, rainbow trout can effectively be stunned by manual percussion or electrical stunning. Consciousness can be monitored by the absence of opercular movements or the eye-rolling reflex, which are lost approximately at the same time as neurological responses like VER. For safeguarding animal welfare during stunning and killing of rainbow trout in conventional production processes, the stunning process requires careful attention and the operating personnel need to be trained in using the stunning devices and recognising indicators of consciousness.

Tissue damage in organic rainbow trout muscle investigated by proteomics and bioinformatics.

The response to tissue damage is a complex process, which involves the coordinated regulation of multiple proteins to ensure tissue repair. In order to investigate the effect of tissue damage in a lower vertebrate, samples were taken from rainbow trout (Oncorhynchus mykiss) at day 7 after damage and proteins were separated using 2DE. The experimental design included two groups of rainbow trout, which were fed organic feed either with or without astaxanthin. In total, 96 proteins were found to be affected by tissue damage, clearly demonstrating in this lower vertebrate the complexity and magnitude of the cellular response, in the context of a regenerative process. Using a bioinformatics approach, the main biological function of these proteins were assigned, showing the regulation of proteins involved in processes such as apoptosis, iron homeostasis, and regulation of muscular structure. Interestingly, it was established that exclusively within the astaxanthin feed group, three members of the annexin protein family (annexin IV, V, and VI) were regulated in response to tissue damage.

Inflammatory and regenerative responses in salmonids following mechanical tissue damage and natural infection.

Locale responses in muscle tissue against either a sterile tissue damage or infection were compared in salmonid fish in order to examine the inflammatory responses and regeneration of tissue. From higher vertebrates both damage and infection are known to cause inflammation since DAMPs released from injured cells as well as PAMPs from the surface of pathogens are immunogenic. To examine this in salmonid fishes, Atlantic salmon (Salmo salar) were infected with Moritella viscosus, the causative agent of winter ulcer. Muscle tissue was sampled from infected fish at 4, 7 and 14 days post infection. Samples were obtained from site of lesions and from locations without clinical signs of disease and lesions. The tissue damage was performed in rainbow trout (Oncorhynchus mykiss) by applying sterile needles to skin and muscle tissue to one side of the fish. Samples were taken 7, 14, 21, 28 and 42 days post injury from the injured side and non-injured site (internal control). From both infected and damaged fish, samples were subject to real-time RT-PCR for measuring the expression of IL-1beta, IL-8, IL-10, Hsp70, iNOS, TGF-beta, TLR-5m, TLR-9, TLR-22, TGF-beta, MMP-2, CTGF, myostatin-1alphabeta and collagen-1alpha which are coding for immunological factors and tissue regeneration. Locale, inflammatory responses were seen as strong up-regulation of IL-1beta and IL-8 in both groups of fish, but it was more pronounced in infected fish. Expression of the toll-like receptors showed induction of TLR-5m following infection, but TLR-9 and TLR-22 following damage. Further, in both studies the regenerative genes TGF-beta, MMP-2, CTGF, myostatin-1alphabeta were induced, but showed different kinetics. Collagen-1alpha was only induced in infected fish, probably due to heavier tissue damage in these.

Fin erosion on rainbow trout on commercial trout farms in the United Kingdom.

Fish weighing less than 30 g and more than 100 g were sampled from 38 rearing units on 10 commercial farms growing rainbow trout for the table market. A fin index was calculated for each of the eight rayed fins on 949 trout by dividing their length by the standard length of the fish. There was a large range in the indices of all eight fins. The fin indices of the small and large fish were compared, controlling for farm effect. With the exception of the dorsal fin, all the indices were larger for the small fish than for the large fish, but the magnitude of the difference was greater for some fins than others. In comparison with the fins of wild fish, the pectoral and dorsal fins appeared to be most eroded and the damage to these fins was evident even in the small fish. The erosion of the caudal, anal and ventral (or pelvic) fins was more prominent in the larger fish. Variations in the fin indices of the caudal, anal and ventral fins suggested that there was little variation between rearing units on the same farm, but that there was significant variation between individual fish in the same rearing units, and between fish on different farms.