CalCOFI Reports, Vol. 11, 1967 - California Cooperative Oceanic ...

20 CALIFORNIA COOPERATIVE OCEBPTIC FISHERIES ISVESTIGATIONSgiven size the rate of intake by weight on small foodorganisms is constant for as long as 1 hour after thestart of feeding, whereas the rate of intake on largeorganisms starts at a much higher level and declinesrapidly. In less than an hour it is at a lower level thanthe constant rate on small organisms. Such information,along with the answers to a number of relatedquestions, the effect of light intensity and temperatureon feeding rates, for example, will lead to an understandingof what variations in plankton abundancemeans to the fish in terms of food availability.Feeding, Growth, Bespiration, and Carbon Ctilizaiionof Eupliaicsiid Nzrinap. An experimental studywas made of the biology of the euphausiid shrimp,Eicphnnsia pacifica, describing growth, feeding, respiration,molting, and the efficiency with which it incorporatescarbon from its food into body tissue.Among planktonic organisms in the food web of theoceans, euphausiid crustaceans rank high in abundanceand importance. They are food for a varietyof fishes, ranging from sardine and jack mackeralto tunas and salmon, and are the chief food of baleenwhales.The experimental studies were dependent uponsuccessful maintenance of euphausiids in the laboratory.Techniques were developed that permitted normalgrowth and development of euphausiids in thelaboratory j some experimental animals were kept forover one year.The euphausiid shrimp studied. E. pacifica, is anomnivorous feeder, utilizing both algae and smallzooplankton animals. In the laboratory, crustaceannauplii seemed to be preferred food over unicellularalgae, but both were eaten when arailable.Growth in euphausiids, as in all crustaceans, is accompaniedby molting. Euphausiids kept in the laboratoryat temperatures similar to those at which theanimal lives in the sea (9-15°C) were observed tomolt on the average every 5 days. The dry weight ofeach molt is approximately 10 percent (range 4-14percent) of the dry weight of the tininial which producedit. Molts contained approximately 46 percentash, 17 percent organic carbon, and 2.5 percent organicnitrogen. Each molt contained about 4 percent of theorganism’s carbon, 2 percent of its nitrogen.Assimilation of ingested carbon (digestion) appearedto be high, usually over 80 percent, as judgedfrom tracer experiments with carbon-14. Respirationaccounted for the major portion of the assimilatedcarbon-62 to 87 percent. The long tertii loss of carbondue to molting ranged from 6 to 11 percent. Thefraction of assimilated carbon calculated to appearin eggs was 9 percent. In young individuals withrapid growth, incorporation of assimilated carbon intobody tissue was as high as 30 percent, in older individualswith slower growth it was as low as 6 percent.Calculations from an oceanic population gave 9 percentas level of incorporation of organic carbon intotissue (excluding eggs and molts) over the life spanof the animal.