TABLE 1. — Size, food intake, and food conversion, at cumulative 

 intervals, of Icichthys lockingtoni maintained in the laboratory 

 over a 151 -day period. 



'Based on 90% water content. 



period ending on 5 February when the fish's 

 weight reached a maximum, /. lockingtoni in- 

 gested 38.9 g of food (dry wt) and gained 34.0 g ( wet 

 wt) for a food conversion of 1.1. 



The fish swam slowly and continuously most of 

 the time but infrequently hovered in one position. 

 The short ( 12.6% SL, 168 mm SL), fanlike pectoral 

 fins were the primary propulsive elements when 

 the fish cruised slowly in the tank. Each pectoral 

 fin was flapped in a semirotary manner, alter- 

 nately to the opposing fin, at approximately 1 

 stroke/s. At short-term increased speeds, the pec- 

 toral fins were held against the body and thrust 

 obtained by sinuous movements of the posterior 

 trunk and caudal region. The small (6.5% SL, 168 

 mm SL) pelvic fins were actively used during 

 swimming especially in braking and turning. As 

 mentioned, the fish was adept at swimming for 

 short distances upside down and at other attitudes 

 about its longitudinal axis. 



The weight of the fish in seawater (20°C, 33%o) 

 immediately after death was 0.36 g or 0.66% of its 

 weight in air (slight negative buoyancy). 



Lipids constituted 4.9% of the dry weight of the 

 spine, 10.6% of the skull, 17.0% of the viscera, and 

 4.4% of the flesh. Spine lipids made up 2.2% of the 

 total body lipids, skull lipids 2.9%, visceral lipids 

 35.3%, and flesh lipids 59.6%. 



Discussion 



The stromateoid characteristic of associating 

 with pelagic coelenterates as juveniles is particu- 

 larly well developed in/, lockingtoni. Many of the 

 small ( <200 mm SL) specimens captured have 

 been taken with medusae (Fitch 1949; Haedrich 

 1966; Fitch and Lavenberg 1968). The locomotor 

 behavior and feeding behavior of Icichthys re- 

 corded in this report are traits well suited for liv- 

 ing with medusae. The ability to swim at various 

 attitudes about the longitudinal axis and to hover 

 and maneuver using the paired fins would be ad- 



vantageous in moving among and avoiding the 

 stinging tentacles of medusae. The grasping of 

 large objects followed by a rolling and twisting of 

 the body appears to be a feeding pattern especially 

 appropriate for tearing chunks from the tentacles 

 and other tissues of coelenterates. Haedrich (1966) 

 reported that the stomachs of Icichthys often con- 

 tain siphonophore remains. A feeding behavior 

 also consisting of grasping objects and twisting 

 the body has been observed (R. L. Haedrich pers. 

 commun.) in two other pelagic centrolophids, 

 Hyperoglyphe perciforma (Mitchill) and 

 Schedophilus medusophagus. 



The food conversion values for Icichthys of 2.7 

 for the 151-day period and 1.1 for the initial 90-day 

 period are comparable to or, in the latter case, 

 more efficient than average total conversions 

 (1.75-2.7) reported by Phillips (1972:19) for brook 

 trout and brown trout fed a variety of diets at 

 temperatures ranging from 8.3° to 15.6°C. The 

 feeding rates of 0.4-1.4% for /. lockingtoni were 

 lower than those of 2-3% at which maximum con- 

 version occurred in channel catfish (Tiemeier et al. 

 1969). Useful comparisons between different ex- 

 periments and different species are limited since a 

 variety of physical and biological factors influence 

 energy requirements and conversion efficiencies 

 and since food conversions, as calculated here, are 

 less meaningful and often different from caloric 

 conversions (Phillips 1972). The most important 

 result of the present study, however, is that the 

 conversion efficiency of/, lockingtoni did change, 

 generally declining with age of the fish (see be- 

 low). 



Limited success has been achieved in maintain- 

 ing pelagic stromateoids in the laboratory. Maul 

 (1964) recorded rapid growth in two species of cen- 

 trolophids Schedophilus (= Mupus) maculatus 

 and Schedophilus ( = Mupus ) ovalis, fed on a diet of 

 shrimp in a large (700-liter) aquarium. The former 

 species increased in weight from 7 to 95 g in 61 

 days, andS. ovalis increased in length from 100 to 

 198 mm SL over the same period. R. L. Haedrich 

 (pers. commun.) has kept two other centrolophids, 

 S. medusophagus and Hyperoglyphe perciforma, 

 for 2- to 3-mo periods in small (40- to 100-liter) 

 tanks at Woods Hole Oceanographic Institution. 

 D. Gruber at the Southwest Fisheries Center in La 

 Jolla has hatched and reared a series of larvae of/. 

 lockingtoni (E. H. Ahlstrom pers. commun.). One 

 larva that hatched on 12 June 1975 at a notochord 

 length of 3 mm grew to 90 mm SL by 30 August 

 1975 (80 days). 



455 



