Jan Raa

Fish silage: A review

Based on a review of various production principles of fish silage, this paper discusses the prospects of introduction of this method, as an alternative to fish meal, to utilize low value fish and waste products, particularly in developing countries. The paper covers the biochemistry, microbiology, and nutritional aspects of fish silage, as well as production technology and economy.

Characteristics of two trypsin type isozymes isolated from the Arctic fish capelin (Mallotus villosus)

1. Two trypsin-like enzymes, assayed by their amidase activity with N-alpha-benzoyl-DL-arginine-p-nitroanilide (DL-BAPNA) as the substrate, were isolated from the gut of the arctic fish capelin (Mallotus villosus). 2. Purification involved affinity chromatography (Benzamidine-CH-Sepharose 4B) of the 30 to 70% (NH4)2SO4 precipitation fraction of a crude extract of the gut, followed by DEAE-Sephadex chromatography, yielding two enzymes, designated Enzyme I and II. 3. Both enzymes had MW of about 28,000 as determined by SDS-electrophoresis. Their isoelectric points were 5.6-5.9 (Enzyme I) and 5.1-5.3 (Enzyme II) and they had similar amino acid composition. 4. Both enzymes were inhibited by standard trypsin inhibitors including the serine protease inhibitor phenylmethyl sulphonyl fluoride (PMSF), but not by the chymotrypsin inhibitor L-1-tosylamide-2-phenylethyl chloromethyl ketone (TPCK). 5. The enzymes had a pH optimum of 8-9 and their stability was not affected by CaCl2. Low pH (2.3) caused an initial rapid loss of enzyme activity, followed by relatively slow decomposition of the activity remaining after 1 hr at 4 degrees C. 6. The enzymes had an apparent temperature optimum of 42 degrees C, resulting from rapid self digestion at higher temperatures.

Solubility and enzymatic solubilization of muscle and skin of capelin (Mallotus villosus) at different pH and temperature

Abstract 1. 1. The breaking strength of capelin skin increases in the pH range from 6 to 10. 2. 2. Digestive enzymes in capelin degrade protein in the native skin at pH below 6, but not at neutral or alkaline conditions. 3. 3. The digestive enzymes release proteins with high molecular weight when acting on muscle tissue at neutral pH. 4. 4. Adjusting the pH to 4 facilitates a chemical/enzymatic dissection of skin and myocommata and simultaneously minimizes solubilization of muscle protein.

Biochemical Ecology of Psychrotrophic Strains of Vibrio anguillarum Isolated from Outbreaks of Vibriosis at Low Temperature

Summary Four strains of the fish pathogen Vibrio anguillarum have been isolated from rainbow trout ( Salmo trutta ), salmon ( Salmo salar ), coalfish ( Gadus virens ) and eel ( Anguilla anguilla ) kept captive at water temperatures of 1–4°C for aquaculture or other purposes in the vicinity of Tromso, Norway. Biochemically, they all closely resemble a reference strain, V. anguillarum NCMB 6. The only important exception was that our strains have lower cardinal temperatures for growth, namely 0°C (minimum), 15–18°C (optimum) and below 30°C (maximum), as opposed to an optimum of 30°C and a maximum of 30–40°C, respectively, for the reference strain. The 4 isolates grew optimally in media containing 2% NaCl, with outer limits for growth at 0.5% and 5% NaCl. The viability was quickly lost in nutrient media without inorganic salt, in membrane-filtered seawater and by freezing or freeze-drying. The outer pH limits for growth were 5 and 9, respectively. Our strains showed enhanced anaerobic growth yields in the presence of trimethylamine oxide (TMAO). When examined with immunochemical methods all the strains, including the reference strain, showed serological cross-reaction, but they clearly differed in antigenic structure.