The effects of stress and storage temperature on the colour and texture of pre-rigor filleted farmed cod (Gadus morhua L.)

This experiment deals with the effects of pre‐slaughter stress and storage temperature on muscle pH, fillet contraction, colour and texture in pre‐rigor filleted farmed cod fillets. The fish were either sedated with a low dose of MS‐222 (14.3 mg L^?1) (unstressed groups) or exposed to the air for 3 min (stressed groups) before being submerged in a benzocaine bath (150 g L^?1). The fish were then killed by a blow to the head, their gills cut, filleted and finally stored at either 4 or 20°C. The stressed groups had significantly lower pH values after slaughter (pH=7.0) than the unstressed groups (pH=7.3). This difference was maintained until post rigor for the fish stored at 4°C, but at 20°C it was immediately overshadowed by a decrease in pH caused by temperature‐dependent processes. The length contraction and changes in registered colour values were more pronounced at both the higher temperature and the higher level of pre‐slaughter stress. Again temperature dominated, but significant and consistent effects were registered from stress. No significant effects of stress on texture post rigor were observed. It is concluded that high storage temperature masks the majority of effects caused by pre‐slaughter stress on the measured variables. Stress management protocols, however, are important when the fillets are kept at the common storage temperature of 4°C.     

Evaluation of feed protein quality by measuring plasma free amino acids in Atlantic salmon (Salmo salar L.) after dorsal aorta cannulation

Two successive experiments were conducted in order to assess plasma free amino acid (FAA) profiles as a method for evaluating protein quality of fish feeds for Atlantic salmon, Salmo salar (L.). In experiment 1, the importance of meal size and inter‐fish variation was assessed by using dorsal aorta cannulated fish and diets that contained different sources of fishmeal (menhaden versus herring) which in the case of herring, had been dried at either 70 or 100 °C. In experiment 2, an attempt was made to mimic a production situation by comparing the FAA profiles in salmon fed diets containing two commercially available fishmeals that had been produced in accordance with industrial standards (Norse‐LT94® and NorSeaMink®; Norsildmel AL, Fyllingsdalen, Norway). FAA profiles in plasma 6 h after feeding were compared with feed true protein digestibility as determined in mink. Cannulated fish, held in individual tanks, were hand‐fed twice daily to pellet rejection (satiety) and daily records of the actual rations consumed were maintained. A total of 24 different amino acids and other amino‐containing compounds were detected using high‐pressure liquid chromatography. Morning and evening meal size showed significant correlations. Meal size had a significant effect on blood levels of the majority of essential free amino acids (EAA) as well as the total sum of FAA (TFAA). In experiment 1, a marked inter‐individual effect was found, possibly because of incipient sexual maturation. FAA profiles were therefore corrected for meal size by linear regression while repeated sampling via the permanently implanted cannula allowed paired comparisons of the different test diets, minimizing inter‐individual variation. Significant differences in plasma FAA profile, EAA and TFAA were detected between fish fed all diets in both experiments. The preceding parameters for fish ingesting each feed were directly related to their respective mink protein digestibility in experiment 1, but not in experiment 2. Our results show that dietary protein quality can be differentiated by the aforementioned protocol, and by using fish with a low metabolic rate feed qualities could be ranked correctly as in experiment 1.     

Resistance to antibiotics in the normal flora of animals.

The normal bacterial flora contains antibiotic resistance genes to various degrees, even in individuals with no history of exposure to commercially prepared antibiotics. Several factors seem to increase the number of antibiotic-resistant bacteria in feces. One important factor is the exposure of the intestinal flora to antibacterial drugs. Antibiotics used as feed additives seem to play an important role in the development of antibiotic resistance in normal flora bacteria. The use of avoparcin as a feed additive has demonstrated that an antibiotic considered "safe" is responsible for increased levels of antibiotic resistance in the normal flora enterococci of animals fed with avoparcin and possibly in humans consuming products from these animals. However, other factors like stress from temperature, crowding, and management also seem to contribute to the occurrence of antibiotic resistance in normal flora bacteria. The normal flora of animals has been studied with respect to the development of antibiotic resistance over four decades, but there are few studies with the intestinal flora as the main focus. The results of earlier studies are valuable when focused against the recent understanding of mobile genetics responsible for bacterial antibiotic resistance. New studies should be undertaken to assess whether the development of antibiotic resistance in the normal flora is directly linked to the dramatic increase in antibiotic resistance of bacterial pathogens. Bacteria of the normal flora, often disregarded scientifically, should be studied with the intention of using them as active protection against infectious diseases and thereby contributing to the overall reduction of use of antibioties in both animals and humans.     

Evaluating bioencapsulation of florfenicol in rotifers (Brachionus plicatilis)

The rotifer Brachionus plicatilis is one of the most important live‐feed organisms used in the larval culture of marine fish. Bioencapsulation of florfenicol in rotifers was investigated by delivering it directly to the organisms as particles and the doses ranged from 50 to 1000 mg L^?1. Analysis of the florfenicol concentrations in rotifers was performed using high‐performance liquid chromatography. The uptake increased with the dose and the enrichment time, and the highest concentration achieved in this study, 1.25 ng rotifer^?1, was obtained using a dose of 1000 mg L^?1 and 150 min of enrichment. The optimal time for satisfactory enrichment of rotifers with florfenicol was found to be dose dependent and ranged from 30 to 120 min for doses between 400 and 800 mg L^?1. The parameters affecting the concentrations achieved in rotifers were the size of the florfenicol particles, enrichment time and dose.     

Cultivation of the spotted wolffish Anarhichas minor (Olafsen) – a new candidate for cold-water fish farming

The spotted wolffish Anarhichas minor (Olafsen), with its rich and tasty fillets, popular skin and high growth rates in captivity, is a promising candidate for cold-water aquaculture. We have established a production line for the wolffish during 5 years of active research on the biology of the species. Our broodstock, sampled from the Barents Sea, has mainly spawned during autumn. The females must be stripped as soon as possible after ovulation. The best egg batches have shown c. 100% fertilization and survival rates between 60% and 80% during the 800- to 960-daydegrees-long incubation period. Rearing temperatures of 6 °C, 8 °C, ambient and decreasing temperatures have turned out to be satisfactory for survival. Treatment with 150 p.p.m. glutardialdehyde twice a month is recommended to control microorganism growth on eggs. Premature hatching has been a problem in individual egg batches; the reasons are not fully understood. Normally hatched individuals are ≈ 22 mm long and well developed, with a small yolk sac, which is completely resorbed after about 4 weeks at 6–8 °C. The fry have been successfully start fed on formulated feed as well as Artemia. Highest early growth rates have been noted at 8 °C, but overall survival was best at 6 °C. On-growth of spotted wolffish juveniles fed formulated dry floating feed at low temperatures in shallow raceways has been promising. After 2, 3 and 4 years, the mean weights of the first generation produced in aquaculture were 0.7, 2.7 and 5.1 kg respectively. These individuals now make up the broodstock at a recently established commercial production facility.