Anaesthetics are used widely to facilitate the handling of fish in commercial fish farms and in experimental studies. Anaesthetized fish may be marked and measured without severe skin damage which might reduce their viability after release. Increasing the ease of handling speeds up measuring and marking, benefiting both the fish and tlie handler. In experimental studies on fish, operations such as the implantation of electrodes or gonadectomy cannot be performed without full surgical anaesthesia.The main features required of any fish anaesthetic are efficacy, wide margin of safety between anaesthetic and toxic dose levels, ease of use, safety to fish and operators and availability without prescription. The most widely used anaesthetic for fish is MS 222 (Sandoz) (Ethyl m-aminobenzoate sulphonate) which is available in crystalline form and is highly soluble in water (solubility 11 per cent). Its anaesthetic properties have been discussed by Bell (1967) and Dick (1975) and others. However, it has several disadvantageous features including high price and possible danger to the health of operatives. Wedermeyer (1970) has shown that anaesthesia with unbuffered MS 222 can result in a marked stress effect (as measured by inter-renal ascorbic acid depletion as a result of the production of adrenocorticotrophic hormone (ACTH) by the pituitary). This effect was reduced if the MS 222 solution was buffered to pH7 and was also less marked with benzocaine, another anaesthetic.Both MS 222 and benzocaine (ethyl p-aminobenzoate) are homologues of benzoic acid. Benzocaine, however, lacks the sulphonate group (H SO3CH3) which is present in MS 222. This accounts for a difference in solubility of the two compounds (benzocaine is only 0-04 per cent soluble in water) and also explains why a solution of MS 222 in distilled water, at normal working concentration (30 parts per million) is acid (pH 3.8). The addition of benzocaine to distilled water has little effect on the pH. Where MS 222 is buffered to pH7 it exists in its free base form (ethyl m-aminobenzoate) which is chemically very similar to benzocaine (ethyl p-aminobenzoate).Benzocaine does not produce the initial excitement usually seen when fish are anaesthetized with unbuffered MS 222, possibly because the pH is unchanged. The fish are rapidly sedated and quickly become less responsive to external stimuli. Recovery from benzocaine anaesthesia is as rapid as with MS 222; in one experiment a 30 cm rainbow trout which had been anaesthetized for one hour was swimming again three minutes after being returned to the water. The severity of the effects of any anaesthetic on fish depend on the concentrations used and on the exposure time and should not be so great in naturally buffered hard waters. With regard to the effects of this anaesthetic on the operator, benzocaine is widely used in human medicine, particularly in throat lozenges where doses of up to 500 mg per day are permitted.

Carotenoid pigment profiles were determined in muscle tissue extracts of anadromous and nonanadromous brown trout (Salmo trutta). In nonanadromous fish, zeaxanthin, lutein, astaxanthin, canthaxanthin, and two unidentified pigments were detected in some or all individuals. In anadromous fish, only astaxanthin and lutein were detected. On the basis of carotenoid pigment profiles, it was possible to distinguish the anadromous and nonanadromous individuals examined in this study with complete accuracy.

The salmon and trout farming industries are relatively new, expanding industries in the UK. Describes their current status and looks to the future by examining areas where progress is currently being made or where problems exist.

No abstract

Freeze branding using liquid nitrogen as a coolant was carried out on salmon parr and a sequential histopathological study was carried out for 16 weeks. The initial darkening of the brand area was due to destruction of melanophore control but the later, more diffuse, pattern was related to the invasion of the area of the stratum spongiosum and hypodermis by melanin containing cells such as are commonly found in healing teleost wounds. The traumatic damage was completely resolved well before the end of the experiment, suggesting that freeze branding is a particularly suitable short term batch marking method.