Energeticsof the Sablefjsh,Anoplopoma Fimbria, UnderLaboratory Conditions KatfgteeggM. SggfiIivagg Scoppatggstttggttoo of Ooaaggography Introduction Laboratory energetics studies can provide important physiological in- formation not generally obtainable from field studies. The range of growth, metabolic and excretion rates measured under controlled labora- tory conditions offers insights into the physiological capabilities of a marine fish; one may then better understand the physiological and ecological functions of the fish in its own environment. Energetics studies of A. fimbria were initiated to learn more about energy allo- cation of a reTativeTydeep-living fish. A. fimbria has an extremely broad geographicdistribution along the contin~enta slope, occurring from Baja California, Mexicoto the Bering Seaans westwardto Japan. Its bathyfffetric distribution also is broad, extending from surface waters in the northernmost range to 1550 meters off southern California Hart, 1973; Phleger et al., 1970!. A. fimbria are exploited cofntter- cially throughout their range, and are sold on Canadian,Japapese and domestic markets. Because they have no swimbladder, A. fimbria can be brought to the surface in good physiological condition and maintained in chilled aquaria for extended periods of time, Field data have beencollected on food relationships and general popu- lation ecology of A. fimbria off southern California Conway,1967; Phleger et al., 1970!, and off Oregon and Washington Holmberg and Jones, 1954; Pruter, 1954!. Large nurrbers of A. fimbria were reared in large floating pens off British Columbia;this work is summarizedby Kennedy 1974!. However, growth, metabolic and excretion rates of indi- vidual fish have not been determined. The goal of the present study was to examinethe physiological capabili- ties of A. fimbria collected off southern California and maintained in chilled aquaria on varying ration levels. A laboratory study of the energy allocation of starved vs. fed fish can offer insight into the 106 effects of lower food supplies that may be associated with greater depths, The results wil'1 be presented in four sections: I! diurnal patterns of standard metabolic rates in starved vs. fed A. fimbria, ! measurementsof amaonia excretion in fed and starved A. fimbria, ! respiration rates of A. fimbria with varying body size, and at low oxygen tensions, and ! growth rates on varying ration size. Materials and Methods A. fimbria were collected by setline in La Jolla Submarine Canyon off San~Dego, Cai i Pornis at a depth of 466 enters. Prior to the experi- ments, fish were held in the laboratory for three weeks in 2100-liter tanks containing chilled running-seawater. The running chil led seawater system exhibited seasonal fluctuations from 6.0'C in the winter to 11,0'C in the sugimger. All tanks were in a darkened enclosure and were kept covered to minimize disturbances and to eliminate light. A. fimbria were confined individua'1ly by nylon mesh barriers to minimize activity and identify individuals. All fish were fed chopped mackerel and squid prior to the experiments. Three treatment groups were used: I! high- ration fish fed 15%of their %et body weight per week, ! low-ration fish fed 7X of their wet body weight per week, and ! starved fish. Uneaten food was removed after two hours, dried and weighed for calcu- lation of ingestion rates. Fish were weighed every two weeks in air, a process which required about four minutes of handling time. This report represents preliminary findings of a large-sca'le laboratory experiment involving IS fish per treatment group! lasting 36 weeks. High ration level was determined by daily feedings of mackerel and squid to estimate maxixmmingestioti levels in the laboratory. Respiration measurementswere made in 64 .5-liter chambers equipped with a circulating pump and a Yellow Springs Instruments Oxygen Electrode. Chambers had a built-in filtration system, and a port for extracting water samples for aanonia determinations. Oxygen electrodes were cali- brated daily witn 02-saturatedand N2 -purgedseawater. Fish wereal- lowed to acclimate to chambers for 24 hours before beginning experi- ments, and individual fish were kept in a chamber for seven days, with six days of experiments following one day of acclimation. The chambers were either flow-through or closed systems; the appropriate chamber blanks were run to determine microbial metabolism. Respiration rates were expressed in mil'ligrams oxygen per kilogram wet weight per hour. Ammoniadeterminations from water samples extracted periodically from chambers were done by spectrophotometric assay Strickland and Parsons, 1973 ! . Agnnonia excretion rates are expressed in mi 1'ligrams nitrogen per kilogram wet weight per hour. Results Diurnal patterns of oxygen consumption in starved and fed A. fimbria. Oxygen consumption was measured in an open respirometry system for two A, fimbria, one starved for three weeks, and one fed IS% of its wet weigggt pet week for three weeks prior to the experiment. Dacil fish was acclimated to the respirometry chamber for 24 hours prior to the experi- ment. The fed fish was fed on the following day, designated day 1, Oxygen consumption by both fish was monitored on days I, 2, 4, and 6. 107 There was a pronounceddiel pattern in respiration rate of the fed fish, with oxygen consumption being the highest between 2400 and 0100 Figure 1A!. This pattern remainedthe samethroughout the week,but absolute rates of oxygen consumption decreased on the fourth and sixth days of feeding Figure 1A!. In contrast, the starved fish showedno diel variation in respiration rate, and its respiration rate was much lower, about one-third as high as the maximumrates of the fed fish Figure 1B!. Onthe fourth and sixth daysafter feeding, daytimeres- piration rates of the fed fish were comparableto those of the starved fish. 20 O OXZ X OIOO ~ X 4J C9 X 0 0200 0800 l400 2000 TIME OF DAY hour! Figure 1: A. Diurnal standard metabolic rates for A. fimbria on days 2, 4 and 6 after being fed 15X ration on day 1. Fish weighed 1,4 kg and had been in aboratory for 6 weeks. B. Diurnal standard meta- bolic rates for starved A. fimbria. Fish weighed 1.01 kg and had been in laboratory 6 weeks, and starved for 3 weeks. 108 Other fish examinedfollowed this sametrend, with fed fish having a 30$ to 50%difference betweenday and night respiration rates; however, peak oxygen consumption rates occurred at times between 1900 and 0300. Starved fish showed very little change in oxygen consumption rates throughout the day, or throughout the week after the second week of starvation. The second week of food deprivation resulted in more erratic respirat on rates on both diurnal and weekly scales, Measurementsof ammoniaexcretion in fed and starved A. fimbria. AnInoniaexcretion rates of five A. fimbria were monitored over a six-day period Figure 2',. Three of the fish were starved, and the two re- mainingfish rece~ived7%and 15% of their bodyweight, respectively . Thesefish were fed on the morningof day 1. Water sampleswere col- lected initially four to six hours after feeding, and every eight to ten hours afterwards. Water temperature was constant at 10'C. In fed fish, nitrogen excretion rates remainedelevated for up to three days after feeding, Peakexcretion rates of 20 mg N-kg h occurred 12-1Shours after feeding Figure 2!, Sy the end of the week, excre- tion rates of fee fish were the same as those for starved fish. Pat- terns of nitrogen excretion suggest. that A, fimbria does not return to the post-absorptive state for up to four Says after feeding. This period of elevated ammoniaexcretion rates correspondsto the period of elevated oxygenconsumption rates following feeding. Respiration rates of A. fimbria with varying body size and at low oxygen tensions. Oxygenconsumption measured in an open respirometry systemat 8,0'C showeda decrease in the weight specific respiration rate with increase in body mass Figure 3!. Measurementsrepresent an averageoxygen consumptionrate over 3-12 hours for fish in a post-absorptive state between 0600 and 1800. All fish were acclimated to the chamber for 24 hours. Thesolid line is representedby the equation y = -43x + 192.4 wherey is weight specific metabolic rate and x is log body mass!. The regression co-efficient r! is -0.73. lhe size range included mature generally fish greater than 1800grams! and inIiiature individuals. Theallometric equationE = aMb whereE is rate of oxygenconsumption, a is a proportionality constant and M is body mass, yields a value for b, the exponent, of 0.81+0.03 S,D.!, Whenthe allometric equation is plotted on double logarithmic paper, it yields a straight line with a slope of b. This b value can be compared to data for different fish species. Values for freshwater fish and salmonids range from 0.70 to 0.85 Srett and Flass, 1973!. Oxygen consumption in closed respiration chamber at 10,0'C for starved and fed A. fimbria showeda decreasein weight specific respiration rate with decreasingoxygen tension Figure4!, Starvedfish, with already depressedrespiration rates, showedlittle changein oxygenconsumption rates over a wide range of oxygentensions. Fed fish showeda sharp de- crease in respiration rates with a lowering of oxygen tension to rates comparablewith s-.arvedfish. In these closed chamberexperiments, anIaonia was chemically scrubbed from the circulating water, thus the build-up of toxic waste products did not compoundthe effects seen in 109 the closed system. Fish did not appear stressed at the conclusion of the closed experiments. K a 5 lO sc ~ K X a Figure 2: Anmonia excretion in milligrams nitrogen per kilogram wet weight per hour over the course of a weekfor starved and fed A. fimbria. Fed fish were fed the morning of day 1. Fish ranged in fn weight from 1,0 to 1,9 kg. 300 d" X O 4- l50 K X 0 O,I i.O 2.0 3.0 SOOY llAS S ko! Figure 3: Oxygen:onsumption in milligrams oxygenper kilogram wet weight per hour vs.