TROPHIC ONTOGENY OF THE LEOPARD SEAROBIN, 

 PRIONOTUS SCITULUS (PISCES: TRIGLIDAE) 



Stephen T. Ross' 



ABSTRACT 



Ontogenetic feeding changes of the leopard searobin, Prionotus scitulus, from Tampa Bay, Fla., 

 showed a shift from planktonic and epifaunal prey in small fish to infaunal prey in larger fish. Smaller 

 fish utilized larval crustaceans, natantians, brachyurans, cumaceans, copepods, and gammarid am- 

 phipods while larger fish showed increasing reliance on the lancelet, Branchiostoma floridae. 



Biomass and linear dimensions of prey increased exponentially with fish size for larger fish, but were 

 relatively constant for small fish. Relative prey biomass was lowest for intermediate-sized P. scitulus 

 (65-95 mm) and increased for both large and small predators so that small individuals were most 

 similar to very large fish in terms of relative prey size. 



The switch to larger prey was preceded by rapid increases in mouth size and intestinal length, and 

 was followed by attainment of minimum reproductive size and greater body weight per unit length. 



Spatial and trophic partitioning appear quite efficient in reducing potential intraspecific competi- 

 tion. 



Our present understanding of energy resource 

 partitioning among metazoans is based primarily 

 on food analyses. However, the study of trophic 

 relationships among fishes is frequently compli- 

 cated by indeterminate gro^vth and the cooccur- 

 rence of several size classes of a species at a single 

 locality. 



A significant degree of prey variability of fishes 

 may be due to size related changes. For instance, 

 Darnell (1958) and Carr and Adams (1973) de- 

 monstrated changes in food habits with increasing 

 size for numerous juvenile marine fishes, and 

 Northcote (1954), Ivlev (1961), Keast and Webb 

 (1966), Wong and Ward (1972), and others have 

 shown a close relationship between morphology 

 (in particular mouth size and shape) and prey kind 

 or size. Such results indicate that inter- and in- 

 traspecific partitioning of energy resources in fish 

 biofacies vary with fish size. 



This study examines ontogenetic changes in 

 trophic biology of the leopard searobin, Prionotus 

 scitulus Jordan and Gilbert, a common nearshore 

 benthic fish in the eastern Gulf of Mexico. Mor- 

 phological and developmental attributes of jaw 

 size, intestinal length, growth, reproduction, and 

 distribution are evaluated in relationship to 

 trophic changes and to intraspecific resource par- 

 titioning. 



MATERIALS AND METHODS 



I collected P. scitulus from three locations in 

 Tampa Bay, Fla. (Figure 1). Numbers offish col- 

 lected and inclusive dates for each station were 

 Station 1, 489 specimens, July 1972-July 1973 

 Station 2, 838 specimens, August 1972-July 1973 

 Station 3, 690 specimens, April 1972-July 1973. 



I examined stomachs from 650 specimens of P. 

 scitulus from Station 3, collected monthly from 

 April 1972 to May 1973. I also identified stomach 

 contents offish from August 1972 collections from 



GULF of MEXICO 



28' 



50 



40 



30 



83 • 50 40 30' 



20 



'Department of Biology, University of Southern Mississippi, 

 Southern Station Box 18, Hattiesburg, MS 39401. 



Manuscript accepted July 1977. 



FISHERY BULLETIN: VOL. 76, NO. 1, 1978. 



Figure l. — Collection localities of Prionotus scitulus in Tampa 

 Bay, Fla., 1972-73. 



225 



