MAGNUSON: ADAPTATIONS OF SCOMBROIDS AND XIPHOIDS 



Unfortunately the energy balances for these 

 species are not known, especially in regard 

 to energy expended for energy encountered 

 as prey and in regard to energy conserved by 

 low activity during times of day that feeding 

 does not occur. However, in my view the most 

 consistent explanation for the adaptations that 

 reduce required speeds among larger scom- 

 broids and the xiphoids is that the speeds must 

 be energetically prudent; and the larger the 

 fish, the less likely this would be possible 

 without a gas bladder and large lifting hydro- 

 foils. Alternatively, but less likely in my 

 opinion, perhaps Brett's and Hunter's estimates 

 of endurance speeds and Shuleikin's estimate 

 of the most efficient speed for migration are 

 overestimates of the physiological capabilities 

 of large scombroids and xiphoids for sustained 

 swimming. 



Larger scombroids are then not able to avail 

 themselves of whatever advantages have been 

 achieved by some smaller species and individuals 

 of scombroids by the loss of a gas bladder. 

 Problems of large size among scombroids be- 

 come either the possibility of an energetically 

 imprudent basal speed requirement to main- 

 tain hydrostatic equilibrium or a loss (Mag- 

 nuson, 1966b; Aleev, 1969), owing to a large 

 gas bladder, in vertical mobility especially near 

 the sea surface. I have observed K. pelamis, 

 a species without a gas bladder, swim vertically 

 upward at burst speeds in the top 10 m of the 

 sea. Large scombroids and xiphoids would be 

 expected to live either (1) deep in the water 

 column where rapid vertical excursions have 

 little effect on gas expansion or (2) imme- 

 diately below the surface and making no rapid 

 upward excursions. The pressure change expe- 

 rienced in an ascent from 10 m to the surface 

 results in a 100% increase in the volume of an 

 unrestricted gas bladder but an ascent from 

 100 to 90 m results in an increase in volume 

 of only 10% . Alternatively, (3) to retain rapid 

 vertical mobility, those with gas bladders and 

 living near the surface would require re- 

 markably strong-walled gas bladders that could 

 maintain the gas at greater than ambient 

 pressures. A casual review of the natural history 

 of large scombroids and xiphoids suggests that 

 all three alternatives are evidenced in one 



form or the other. The most unlikely species 

 would be one with a large, thin-walled gas 

 bladder that also cruised at 10 m below the 

 surface and chased its prey or escaped preda- 

 tion vertically toward the sea surface. 



ACKNOWLEDGMENTS 



My special thanks go to Randolph K. C. 

 Chang at the Southwest Fisheries Center, 

 Honolulu Laboratory, National Marine Fish- 

 eries Service, NOAA for his help in collecting 

 and processing of data throughout the course 

 of this study. I also thank the many employees 

 of the above Laboratory and at the Laboratory 

 of Limnology for their help during many phases 

 of the research and John H. Prescott arid 

 Jerry Goldsmith of Marineland of the Pacific, 

 Palos Verdes, Calif., for help in obtaining 

 morphometric data on Sarda and Scomber. 

 I appreciate the helpful review of the manu- 

 script by Barry S. Muir, Fisheries Research 

 Board of Canada at Halifax, and Robert H. 

 Gibbs, Jr., Smithsonian Institution. Support 

 for the study came almost entirely from the 

 Southwest Fisheries Center, Honolulu Lab- 

 oratory, National Marine Fisheries Service, 

 NOAA (formerly the Bureau of Commercial 

 Fishei-ies Biological Laboratory). 



LITERATURE CITED 



Abe, T., and Y. Takashima. 



1958. Differences in the number and position of 

 two kinds of fin-supports of the spinous dorsal 

 in the Japanese mackerels of the genus Pneiimato- 

 phorus. Jap. J. Ichthyol. 7: 1-11. 



Aleev, Yu. G. 



1963. Funktsional'nye osnovy vneshnego stroeniya 

 ryby (Function and gross morphology in fish). 

 Izd. Akad. Nauk SSSR. Moscow, 245 p. (Trans- 

 lated by Israel Program Sci. Transl., 1969. 268 p.. 

 available U.S. Dep. Commer., Natl. Tech. Inf. 

 Serv.. Springfield, VA., as TT 67-5 139 1.) 



Alexander, R. M. 



1967. Functional design in fishes. Hutchinson, 

 Lond. 160 p. 



1968. Animal mechanics. Univ. Wash. Press, 

 SeaUle, x -I- 346 p. 



Barrett, I., and A. R. Connor. 



1962. Blood lactate in yellowfin tuna, Neothumms 

 macropterus, and skipjack, Katsuwunus pelamis, 

 following capture and tagging. [In English and 

 Spanish.] Bull. Inter-Am. Trop. Tuna Comm. 

 6:231-280. 



353 



