premium for his improved pack which he would 

 need to reimburse the fishermen. In any case, 

 the establishment of a basis for premium fish 

 payment, whether it would be by rated load 

 capacity of a well, by freezing records of a load, 

 or by his visual or chemical inspection of the 

 raw or canned fish, would be difficult. One al- 

 ternative which might be considered in future 

 vessels is design modification which removes 

 the incentive to overpack. 



Effect of Refrigeration on Yield 



It has long been supposed that poor refriger- 

 ation, which can lead to the breakdown of pro- 

 teins and to loss of water retention, should de- 

 crease the yield of canned tuna. Experiments 

 made with the first brine system on the vessel, 

 the American Beauty, showed better yields than 

 were obtained on comparable loads from ice 

 boats, although no records are now available 

 (Mann, 1967). Measurements made on freez- 

 ing brines have at time shown high nitrogen 

 contents, demonstrating the loss of considerable 

 amounts of protein. This would indicate that 

 poor quality and poor yield go hand in hand 

 and that conversely, procedures which improve 

 quality would also increase yield. Therefore, 

 some measurements of yield factors were in- 

 cluded in our freezing experiments. 



Accurate measurements of yield are notori- 

 ously difficult to make because of the big nat- 

 ural variations encountered, especially those 

 involving the cleaning operation. For this 

 reason, and because of the limited amounts of 

 fish available in the experiments, the results 

 should be regarded only as indicative. 



We found that all the tuna collected at sea 

 aboard the MV Lois Seaver (a sister ship to 

 the MV Westport), which had been frozen and 

 stored at temperatures of —5°, 8°, and 14° F, 

 and then canned when landed, gave higher 

 yields than the brine frozen controls. The in- 

 crease was less than 1% in the case of 40-lb. 

 yellowfin but nearly 8% in the case of 14-lb. 

 skipjack (Finch and Crawford, unpublished). 



On storing the tuna for an additional 30 and 

 60 days, at the same temperatures, the yield 

 dropped. In the case of the yellowfin samples, 

 it became less than the original brine frozen 

 control samples, although the skipjack yield 

 was still nearly 6^^ higher when canned 84 



days after catching. There was no difference 

 in yield among samples stored at — 5°, 8°, or 

 14° F. With skipjack frozen rapidly in Free- 

 zant 12, there was a considerable increase in 

 yield on the cooked fish. The overall yield after 

 cleaning showed an increase of nearly 8%, but 

 the yield for the fish which had been held in 

 the well prior to freezing was less than that 

 of the controls. Further experiments on a 

 larger scale should be carried out in which the 

 yield differences should be judged using con- 

 siderably larger quantities of fish to obtain 

 more reliable figures. This aspect is important 

 because it offers a potential prospect of in- 

 creased payment for better refrigerated fish 

 since the canner may recover his costs from 

 his greater case yield. 



Chemistry of Raw and Canned Tuna 



In addition to the direct work carried out in 

 our tuna program, some work has been carried 

 out on certain compounds which occur or are 

 formed in tuna and which are connected with 

 the quality. This sei-ves two purposes: A 

 thorough knowledge of the variations in the 

 amounts of these compounds occurring in the 

 different tunas, and the changes they undergo 

 during catching, refrigeration, and processing, 

 would be valuable in helping to influence them 

 most favorably in the maintenance of quality. 

 Secondly, there is a lack of reliable ways of 

 measuring the quality of raw tuna. Successful 

 development of such measures would not only 

 be of value to research, but could also provide 

 methods by which raw fish quality might be 

 judged. None of the present freshness tests 

 appear to have much application to tuna, and 

 this may be in part because the requirements 

 for the handling and processing of fish which 

 are to be canned are likely to differ in some 

 important ways from the requirements for fish 

 to be used in other ways. A number of com- 

 pounds in tuna have been studied and, of these, 

 the following appear likely to have the most in- 

 fluence on quality. 



Heme pigments, the principal color factors 

 in tuna. — It has been noted that color is an 

 important factor in canned tuna, perhaps the 

 most important. Control of color to give a 

 light, bright, consistent appearance would al- 



