FISHERIES RESEARCH BOARD OF CANADA Translation Series No On the specific gravity of the squid Ommastrephes sagittatus Lamarck. By G. V.

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1 iî\rchive FISHERIES RESEARCH BOARD OF CANADA Translation Series No. 998 On the specific gravity of the squid Ommastrephes sagittatus Lamarck By G. V. Zuev Original title: Lamarck. Ob udel'nom vese karmara Ommastrephes sagittatus From: Trucbr Sevastopol'skoi Biologicheskoi Stantsii, Vol. 16, PP , Translated by the Translation Bureau Foreign Languages Division Department of the Secretary of State of Canada Fisheries Research Board of Canada Biological Station, St. John's, Nfld. 1968

2 The capacity of an organism in a state of static equilibrium depends on the specific gravity of the organism and its alterations with changes in the position of the animal in layers of water with varying densities, temperatures and pressures. Aquatic organisms possess a whole series of adaptations for altering their specific gravity: in fish, this is the air bladder, in cephalopod molluscs - the inner air chamber or light inter-cavity fluid, and in marine mammals - heavy depositions of fat. The buoyancy of cephalopods was the subject of an investigation by E. Denton and J. Gilpin-Brown (1958, 1959, 1961), who studied in the southern part of the Bay of Biscay the density and buoyancy of three species of squids (Verrilliteuthis hyperborea (Steenstrup), Galiteuthis armata Joubin and Helicocranchia pfefferi Massy). It proved to be the case that these squids have remarkable adaptations, reducing their density and providing great economy of effort in movement. Having no cuttlebone or air sac, they have vast cavities, occupying about two-thirds of the body volume and filled with coelomic fluid. The fluids of all three species were almost identical in their contents and properties; density measurements came to 1,010 and 1,012. Studies of this fluid point to a high concentration of ammonia, about 480mM (in sea water only traces of ammonia are present). The ph value of the fluid, equalling 5.2, is undoubtedly connected with the retention in the coelom of ammonia, for living tissue, being permeable to molecular ammonia is relatively impermeable to the ions of ammonia which predominate in an acid medium. An artificially prepared solution of sodium chloride and ammonium chloride in the proportions in which they are encountered in coelomic fluid gives a density very close to the density of coelomic fluid.

3 A similar buoyancy mechanism is also possessed by Noctiluca (Krogh, 1939) in which the high content of ammonium ions not only insures its preservation of tone but also creates buoyancy. Unfortunately Denton and Gilpin-Brown do not indicate the density which according to their data is possessed by squids. Living in the bottom layers of the water, the cuttlefish Sepia officinalis L., for the creation of neutral buoyancy, uses its cuttlebone, the volume of which constitutes 9.3% of the volume of the entire animal whereas in fish the volume of the swimming bladder is not more than 5%. The specific gravity of the cuttlebone is around 0.6. A cuttlefish deprived of a cuttlebone is approximately 4% more dense than sea water. The cuttlebone consists of 100 chitinous lamellae, arranged one above the other and supported by vertical braces. The space between the lamellae forms independent chambers which are separated by membranes running parallel to the lamellae. The cuttlebone chambers are filled with fluid and gas, which move freely within the chambers. Cuttlebones are distinguished not by the weight of dry matter per unit volume, which is always close to 38%, but by the amount of fluid contained in the cuttlebone. The pressure of the gas within the cuttlebone measured underwater at atmospheric pressure equals 0.8 atmospheres. The mass of gas in the cuttlebone remains constant when a reduction occurs in the density of the cuttlebone. A change in the density of the cuttlebone is explained either by the displacement from it or the admission into it of fluid. The constancy of the mass of gas in the cuttlebone is explained by its slow diffusion through the walls of the chambers (Denton and Gilpin- Brown, 1959, 1961a, 1961b). The fluid enters and leaves the cuttlebone through a siphuncular wall which serves in the nature of a barrier to the penetration of fluid. A histological analysis indicates that the siphuncular

4 - 3 - wall contains numerous ampullae, terminating blindly in the cuttlebone and having an outlet to the circulatory system. A very similar system of vessels to this was discovered in the epithelium covering the siphuncular Nautilus (Willey, 1902). In this way, the cuttlefish regulates the respective volumes of gas and fluid within the cuttlebone with the aid of an osmotic mechanism acting through the siphuncular surface of the cuttlebone. In this work a determination was made of the specific gravity of one of the representatives of the pelagic squids, Ommastrephes sagittatus Lamarck. The investigations were made on board the Expeditionary Ship "Akademik Kovalevskiy" during an autumn-winter voyage (November-February) in the Gulf of Aden and the Indian Ocean. Squids, collected during the dark period of the day on the surface of the sea lighted by an electric lamp, were caught in nets and immediately transferred to the laboratory. After being dried on filter paper, the water was carefully removed from the mantle cavity, whereupon their specific gravity was found in air (weighing was done on technical scales with an accuracy of up to 0.01 grams). Volumes were measured in a graduated cylinder with sea water. On determining the volume, the air residues were removed from beneath the mantle and from the cephalic folds, where air bubbles normally collect. Calculations were made using the formula q equals P,where q is the specific gravity of the squid, P is the weight of the squid in air, V is the volume of the squid in water. For determining the specific gravity, 53 squids were used. The range in which variations occurred in specific gravity ( ) is quite large, and is explained by the lack of precision of our measurements (a very small error in weighing or determining volume gives a considerable distortion in the specific gravity).

5 - 4 - The mean value for 53 specimens equalled 1.051; to ensure reliability of the data, specific gravities were determined with an accuracy of up to Subsequently conducted determinations of the specific gravity of these specimens, which had been fixed in a 4% solution of formalin for a period of 4 months indicate that the ensuing changes are very slight. Specific gravity becomes less by approximately (diagram). It will be seen from the diagram that the range of the specific gravity of fixed squids is considerably more narrow ( )4) and that the points are distributed close to the mean (1.0 )41); this is explained by the fact that the results of laboratory experiments conducted ashore are more precise than those obtained at sea. We will examine the relation between the specific gravity of squids and their measurements (mantle length). The mantle length was measured from the apex of the body to the edge of the mantle. series of squids obtained by us ranged from 5.7 to 32.2 cm. The measured Sexual differences existing during the period in question were not taken into consideration. The tendency of the dots to be distributed along the mean line points to a relative constancy in the derived magnitude of the specific gravity (1.05) throughout the entire life cycle. P.1 perlo2 î v.* de st!. Ur. a',,. ae :,. 9., z : ti,» i._..._« p I0 si " variations in the specific gravity of Ommastrephes sagittatus specific gravity of animal; Mp - mean value of Lamarck: q - specific gravity of squids just caught; ql - specific gravity of sea water; L - length of mantle of squid; 1 - specific gravity of squids just caught; 2 - specific gravity of squids fixed in a 4 per cent solution of formalin.

6 5 Determination of the specific gravity of 134 squids O. sagittatus fixed in a 4% solution of formalin, using the weight-volume method gives a variation in the specific gravity from to 1.070, the mean value of the specific gravity being It also proved to be the case that preservation has an unequal effect on changes in the specific gravity of squids of different sizes. The weight of the series measured was broken down into classes, the magnitude of the class interval being 5 cm. In the initial classes (from 5 to 25 cm) the specific gravity value oscillates around the mean value (1.042): the preservation factor is 0.01; in the later classes (from 25 to 35 cm) the specific gravity value falls and its mean value equals 1.033: the preservation factor is 0.02 (table). The change in the preservation factor in relation to the size of the animal can only be explained by having a good understanding of the biology of Ommastrephes sagittatus Lamarck. This variation is evidently associated with variations in the internal structure of organs and tissues. According to our data, the specific gravity of Ommastrephes sagittatus is close to the specific gravity (1.025) of the sea water in which they were caught, exceeding it by 2.5%. Its buoyancy which is close to neutral, remained negative. A reference has been found in the published literature (Denton and Gilpin-Brown, 1961) to the fact that the density of the squid Loligo forbesi exceeds the density of sea water by 4%.

7 6-. Variation in the preservation factor with increases in sizes of squids Ommastrephes sagittatus Lamarck. Measured groups, cm Mean value gravity of Mean value gravity of of specific live squids of specific fixed squids Preservation coefficient In the Red Sea, two larvae of Loligo vulgaris L. were caught; the length of one was 1.1 cm, and of the other cm. In both cases q was 1.04 (preserved material). This can serve as an indirect corroboration of the above viewpoint regarding the constancy of the specific gravity value throughout the entire life cycle of O. sagittatus, for Loligo vulgaris is also a typical pelagic form, inhabiting open areas of the oceans and seas. Of the Cephalopodas-Octopoda the specific gravity was determined in two young specimens of Red Sea octopuses with overall lengths of 18.3 and 7.5 cm (the species were not determined). It turned out that their specific gravity was higher than the specific gravity of squids and comprised and (in fixed animais). The negative buoyancy of octopuses is closely connected with their ecology. The main function of the funnel in octopuses is respiratory; water is continually circulating through the funnel and washing the gills. As an organ of locomotion the funnel is used to a lesser degree, as octopuses lead a relatively sedentary existence, not making any significant migrations.

8 e 7 Bibliography Denton, E. J., Shaw, T. I. and Gilpin-Brown, J. B. Bathyscaphoid Squid. Nature, 1958, vol. 182, N Denton, E. J. and Gilpin-Brown, J. B. Buoyancy of the cuttlefish. Nature, 1959, vol. 184, N Denton, E. J. and Gilpin-Brown, J. B. The buoyancy of the cuttlefish Sepia officinalis (L.). J. mar. Mol. Ass. U.K., 1961, vol. 41. Denton, E. J. and Gilpin-Brown, J. B. The distribution of gas and liquid within the cuttlebone. J. mar. biol. Ass. U.K., 1961, vol. 41. Denton, E. J., Gilpin-Brown, J. B. and Howarth, J. V. The osmotic mechanism of the cuttlebone. J. mar. biol. Ass. U.K., 1961, vol. 41. Krogh, A. Osmotic Regulation in Aquatic Animals. Cambridge, Willey, A. Contribution to the natural history of the Pearly Nautilus. A. Willey's Zoological Results, 1902, Pt. 6, pp Cambridge.