FISHERY BULLETIN: VOL. 69. NO. 1 



Males use a small amount of energy in pro- 

 ducing sperm, but we assume that this is negli- 

 gible. In females, the ova begin to be infused 

 with yolk about age 45 days. The actual dis- 

 charge of eggs occurs at discrete intervals of 

 about 10 days, beginning at age 53 days. We 

 assume that the accumulation of energy for re- 

 production is more continuous than this, there- 

 fore we have shown reproductive energy use as 

 a smooth curve. The reproduction energy curve 

 shown in Figure 12 is based on the maximum 

 fecundity estimate given previously [number of 

 eggs = 4.1 (body length, mm) — 8.9]. A repro- 

 duction energy curve based on our minimum es- 

 timate of fecundity [number of eggs = 4.1 (body 

 length, mm) — 12.0] would be 0.12 cal (3.1 

 eggs) lower per spawning. This would make 

 the minimum estimate 72 Sr of the maximum 

 estimate at the age of first spawning (53 days) 

 and progressively higher in percentage there- 

 after, e.g. 85 9f at the age of fifth spawning 

 (93 days). All our reproduction energy cal- 

 culations take into account the observation that, 

 on the average, mature females extrude the usual 

 number of eggs only one-half of the time and 

 otherwise extrude only one-half the usual num- 

 ber of eggs. 



The amount of energy used in respiration was 

 calculated from the weight-specific respiration 

 equation: R' — 2.1 (dry weight, mg)-"'^^ and 

 from energy conversion factors based on our 

 estimates of body composition. 



We do not know what substrate Metamysidop- 

 sis catabolizes. The organic fraction of the body 

 is largely protein; the storage ])roduct (carbo- 

 hydrate and lipid) content is low. Raymont 

 and Krishnaswamy (1960) observed that the 

 carbohydrate content of Neomysis integer de- 

 creased slightly, from about 1.30 % (of dry 

 weight) to 1.06 ^(, when a marked reduction 

 in feeding occurred. For the same species, Lin- 

 ford (1965) found no significant change in lipid 

 level whether the animals were starved, fed a 

 lipid-free diet, or fed a high lipid diet. Raymont 

 et al. (1968) asserted that N. integer uses pro- 

 tein as an energy source. 



We agree with Linford (1965) that it seems 

 likely that the mysids must live largely on their 

 daily ingestion. We think that the food they 



ingest has composition similar to their bodies. 

 Therefore, our energy calculations assume that 

 they use catabolic substrates in proportion to 

 their presence in the body. This is supported 

 by the results of Jawed (1969). To convert 

 the amount of oxygen used in respiration into 

 the equivalent energy lost as heat we have used 

 the following values for calories lost//il Oq con- 

 sumed (Hawk et al., 1954; Prosser, 1950): 

 protein, 4.5 X 10"^; lipid, 4.7 X lO"'; car- 

 bohydrate, 5.0 X 10 ~^ Therefore, our esti- 

 mate of the average amount of energy used in 

 respiration is about 4.5 X 10""'cal /A O2. 



The cumulative energy used in respiration is 

 shown as the uppermost curve in Figure 12 

 (females) and Figure 13 (males). The area 

 between that curve and the next lower curve 

 represents the catabolic heat loss. These res- 

 piration data were calculated for a temperature 

 of 16° C, which was the median temperature 

 of the natural environment of Metamysidopsis. 

 Our respiration measurements were made in 

 flowing water during the daylight hours. There- 

 fore, they represent basal metabolism + energy 

 expended in active swimming. There is some 

 evidence (Clutter, 1969) that the mysids may 

 be less active at night, even though they con- 

 tinue to swim at all times. For this reason we 

 think that the field population may use some- 

 what less than this amount of energy in respir- 

 ation. 



Our estimated rate of energy loss in catabo- 

 lism is higher than that estimated by Jawed 

 (1969) in his study of nitrogen excretion in 

 Neoviysis rayii. He suggested that protein is 

 catabolized in relatively large quantities, there- 

 fore nitrogenous excretion may provide a good 

 estimate of catabolism. He found an average 

 catabolism of about 2.5 % of body nitrogen 

 per day in adult animals that were probably 8 

 to 10 mg dry weight, that were held at 10° C. 

 The rate for adult Metamysidopsis of average 

 size (0.6-0.8 mg) was 5 to 6 % of the body 

 energy i)er day. This disparity in catabolism 

 may result from diff'erences between the size 

 and between the environmental temperatures 

 of the two species. 



Jawed (1969) showed that about 15 % of the 

 nitrogen was excreted as amino acids. We did 



110 



