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II. Frostfish (Lepidopus caudatus).
This peculiar - looking fish, known in other parts of the English-speaking world as “scabbard-fish,” is found in the Mediterranean and warmer parts of the Atlantic as well as around the Tasmanian and New Zealand coasts. It derives its popular name from the fact that it is thrown up by the sea in frosty weather, and is found dead or dying on the beach. According to one view, it comes ashore voluntarily, as if bent on self-immolation; it has seldom, if ever, been caught alive, and is generally believed to be a deep-water fish. In shape it is long and ribbon-like, and has a bright scaleless skin. Unlike many New Zealand food fishes, it has a distinctive flavour, and partly from this and partly no doubt, from its comparative rarity it is regarded as a delicacy, and sells at 1s. 6d. to 3s. per pound. For the purposes of sale and for cooking it is cut into slices across its long axis; all such cutlets include the vertebral column, and some also include the abdominal cavity. There is a considerable amount of waste matter in the cutlets; thus in an ordinary slice as bought only 85 grm. out of a total of 134 grm. consisted of edible flesh. The residue (36°5 per cent.) consisted of bone, skin, and tough intermuscular septa, although the latter would probably form gelatine during the process of cooking, and should not be considered altogether as waste.
Fat.—The flesh is obviously fatty, and an oily scum forms on the water in which it is boiled; but the fat is unequally distributed, there being much more in the tissues immediately surrounding the abdominal cavity than in the muscles of the sides. In the first sample examined the fat of the dorsal portion or sides of the fish amounted to 4°55 per cent., and that of the ventral to 16°77 per cent. In the second sample there was 7°36 per cent. fat in the sides, and 20 per cent. in the ventral portion. From the culinary point of view, therefore, the frostfish should be reckoned as a fatty fish somewhat akin to turbot. The fat extracted by ether is a yellow-coloured oil, half-fluid at room-temperature, and possessing a smell which recalls that of cod-liver oil. It contains 1 per cent. of nitrogen.
Protein.—Owing to the presence of a considerable amount of non-protein nitrogenous substance, it is not permissible in this case to use the total nitrogen as the basis for calculating the percentage of protein. The following procedure was therefore followed: The residue, after extraction of the fat, &c., by chloroform and alcohol, was weighed and sampled for nitrogen-estimation—thus 10°967 grm. partly dried “sides”
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of fish, representing 37°45 grm. fresh material, was extracted with chloroform and with alcohol; the residue weighed 8°412 grm.; the nitrogen percentage of this was 12°56, which equals 2°807 per cent. of protein-nitrogen in the moist fish, or 17°54 per cent. protein. The total nitrogen of the moist frostfish was found to be 3°6 per cent. Deducting the protein-nitrogen (2°8 per cent.) we obtain 0°8 per cent. of nitrogen belonging to non-protein material. As already stated, the ether-soluble “fat” contains 1 per cent., but even after deducting this value (0°08) we have 0°72 per cent. nitrogen to account for, and, as will be mentioned later, this nitrogen was partly present in a special crystalline substance soluble in alcohol.
Glycogen could not be detected in the samples of frostfish examined; thus 30 grm. was treated by Pfluger's method without positive result.
The main points brought out by the analysis are shown in the following table:—
| Sample 1. | Sample 2. | |
|---|---|---|
| Water, per cent. | 76·8 | 73·5 |
| Solids, per cent. | 23·2 | 26·5 |
| Fat, per cent. | 4·55 | 7·36 |
| Total nitrogen, per cent. | 2·82 | 3·6 |
| Protein, per cent. | Under 17°6 | 17·54 |
| Glycogen | Nil. | |
| Alcoholic extract, per cent. | 0·8 | |
| Ash, per cent. | 1·15 | 1·28 |
The data obtained from analysis of the ventral part of the fish are as follows:—
Sample 1.—Fat, 16°77 per cent.; substances soluble in boiling water (gelatine and salts), 3°7 per cent.; substances insoluble in boiling water (coagulated proteins, &c.), 2°73 per cent. The water percentage was not estimated. These figures are calculated on the assumption that it was the same as in the other parts of the fish.
Sample 2.—24°8 grm. ventral portion of frostfish gave 4°9584 grm. ether-soluble fat = 20 per cent.
Crystalline Substance.—On boiling fresh minced frostfish with 96 per cent. alcohol, and allowing the extract to cool, a fine white crystalline deposit formed. Under the microscope two types of crystals appeared to be present; the more numerous were balls of fine, pointed needles slightly bent or twisted so that they resembled puff-balls, the others were much smaller rounded clumps of indeterminate crystalline matter. At first sight they might be mistaken for leucin and tyrosin. When filtered and allowed to dry in the air the deposit formed a white powder, easily soluble in water. It gave no biuret or Millon's reaction, and did not reduce Fehling's solution. Ammonia caused a slight precipitate. When directly tested the powder gave distinct evidence of carbon, nitrogen, and phosphorus.
While frostfish is undoubtedly of high nutritive value, and an excellent article of diet, the conditions under which the fish is obtained, its doubtful degree of freshness, its high percentage of fat which from its oily nature is apt to become rancid, the presence of a special alcohol-soluble substance at present of unknown nature, all tend to make one careful in advising its use for invalids. Parasitic worms—small, round,
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and coiled like a watch-spring—occur fairly often; they are probably quite harmless.