The success of livebait fisheries for tuna depends to a large extent on the availability 

 of baitfish. In the Hawaiian fishery for aku (skipjack or striped tuna), Katsuwonus pelamis 

 (Linnaeus), the two species of baitfish most comnnonly used are the nehu, Stolephorus purpureas 

 Fowler, and the iao, Pranesus insularunn (Jordan cind Evermann). The nehu, although the less 

 hardy of the two, is the preferred bait. Nehu are generally caught at night by attraction to a 

 light, and both nehu and iao are caught during the day by means of surround nets. Bait is quickly 

 transferred from the nets to livebait wells in the fishing vessels. 1' The period following the 

 transfer of bait is crucial in livebait fishing, for if water circulation in the live -wells is inade- 

 quate and the fish crowd together at the surface or in a corner of the well, considerable mortality 

 may occur. The usual mortality is about 20-30 percent, most of it during the first day, but in 

 some instances it may amount to 50-100 percent. 



Heavy bait mortality is probably due to the interaction of several factors. Loss of 

 scales and collisions with the sides of the tank probably lead, directly or indirectly, to the death 

 of many fish. On the other hand, when fish are confined to a limited space, as they are in the 

 livebait wells, the possible depletion of oxygen to levels causing abnormal respiration and suffo- 

 cation must be considered. This problem of oxygen depletion would be especially acute in those 

 boats (making up the majority of the fleet at present) which employ the method of circulating water 

 through holes in the bottom the well. A few boats possess pumps for circulating water through the 

 live-wells, and nnay perhaps be less concerned with the problem of oxygen depletion per se . 

 Other questions arise, however, particularly in regard to the effect of different flow rates and 

 various degrees of crowding upon the behavior of the fish. The local annual range of temperature 

 is small, but the possibility of a small but sudden rise or fall in temperature, with its concomi- 

 tant effects on respiratory metabolism, must be considered. 



The object of the present study was to analyze, in the laboratory, the oxygen require- 

 ments of the local tuna baitfish in the hope of obtaining basic information which nnight be of value 

 to livebait fisheries. An investigation of oxygen consumption under various conditions was 

 carried out, emphasis being placed on the effects of temperature, flow rates, various degrees of 

 crowding, and the oxygen concentration of the water. In addition, experiments were designed to 

 deternnine lethal levels of oxygen for the fish. 



The author takes this opportunity to thank Dr. P. B. van Weel for his guidance and con- 

 stant encouragement throughout this work. Grateful acknowledgement is made to the staff of the 

 Pacific Oceanic Fishery Investigations for advice and technical assistance. Special appreciation 

 is also due Lester Zukeran and Charles Nakamoto of the Hawaii Marine Laboratory for taking a 

 large share of the responsibility for catching and maintaining the stocks. 



REVIEW OF THE LITERATURE 



An enormous literature exists on respiratory exchange in fish and an extensive review 

 will not be attennpted here. A summary of literature relevant to this study will be presented now 

 with mention of individual publications in connection with the appropriate sections of the work. 

 Suehiro's (1951) study of the lethal limits of oxygen for Japanese sardines and anchovies is the 

 only set of observations known to the author on the respiratory metabolism of baitfishes. Besides 

 measuring lethal values of oxygen, Suehiro made several observations on the amount of oxygen 

 consumed by baitfish in live-wells, ai»d emphasized the superior bait-holding capacity of those 

 bait tanks in which water was circulated by pumps. 



1/ A good description of the Hawaiian livebait fishery is given by Fred C, June (1951, 

 Commercial Fisheries Review 13(2):1-18). 



Note: Financial support for this study came from a U. S. Fish and Wildlife Service 

 fellowship. The material reported forms the greater part of a thesis submitted to the graduate 

 school of the University of Hawaii in partial fulfillment of the requirements for the degree of 

 Doctor of Philosophy. The author at present is a faculty member of the Department of Zoology, 

 Oregon State College, Corvallis, Oregon. 



1 



