Yellowtail Flounder 



Crustacea was the predominant prey of juvenile 

 yellowtail flounder (94.4%). Amphipods (38.8%) 

 were represented by the families Gammaridae 

 (5.2%), Caprellidae (0.5%), Aoridae ( +), Ampelis- 

 cidae (+), and Oedicerotidae (+). The Mysidacea 

 (33.4%) were mostly Erythrops sp. (9.9%). Cuma- 

 ceans (10.2%), decapods (composed of Crangon 

 septemspinosa, 3.4%, and hermit crabs, 0.3%), 

 isopods (1.0%), and copepods ( + ) made up the rest 

 of the crustacean prey. Polychaeta (3.0%) was the 

 only other dietary item noted in yellowtail 

 flounder stomachs. They consisted mainly of 

 Nerediformia (2.1%); most of which were iden- 

 tified as Phyllodoce sp. (0.9%). 



The smallest yellowtail flounder collected (3 cm 

 TL) ate organisms such as gammarid amphipods, 

 cumaceans, and hermit crabs. 



Discussion 



A number of investigators have described the 

 foods of juvenile groundfish. Although many of 

 their studies were not conducted on the same 

 species of fish or in the same geographic area as 

 the present research, they provide evidence that 

 the food of many juvenile fish species is similar. 

 Arntz (1974), for example, studied the feeding of 

 juvenile cod >11 cm FL in the western Baltic. His 

 work showed that juvenile cod feed mostly on 

 small bottom living crustaceans. Daan's (1973) 

 results from studies on cod >8 cm FL in the North 

 Sea also indicate that juvenile cod feed predom- 

 inantly on small benthic organisms. Homans and 

 Needier (1944) and Wigley (1956) included data 

 on the food of juvenile haddock in their investiga- 

 tions. They found that small haddock generally 

 eat crustaceans associated wdth the bottom, and 

 polychaete worms. The diet of several juvenile 

 flatfish species found in the North Sea consists 

 mainly of small benthic crustaceans and poly- 

 chaete worms (Braber and DeGroot 1973). The 

 food of 33 juvenile demersal fish species collected 

 in Long Island Sound, N.Y., was identified by 

 Richards (1963); her data showed that when most 

 inshore fishes are 1 yr old, they feed predom- 

 inantly on the benthos. 



Studies conducted on larval fish indicate that 

 most groundfish species undergo several pelagic 

 stages, and during these stages they feed predom- 

 inantly on planktonic organisms (Rae 1953; 

 Marak 1960, 1974; Laurence 1974, 1977; Last 



1978). During their first year of life the majority of 

 groundfish take up a bottom living habit and feed 

 primarily on the benthos (Graham 1956). Assum- 

 ing that the type of food found in a fish's stomach is 

 indicative of its life stage, then the diet can give 

 some approximation of a fish's age (length) when 

 it makes the transition from pelagic to demersal 

 living. Fish such as cod, for example, have been 

 described as "seeking the bottom" when just over 2 

 cm FL (Hardy 1959) and stomachs from Atlantic 

 cod 3 cm FL examined during this study contained 

 small amounts of sand and benthic gammarid 

 amphipods. Most of their food, however, was 

 identified as copepods and euphausiids, indicating 

 that the transition from feeding on principally 

 plankton to other foods is a gradual change rather 

 than an abrupt one. 



The transition from pelagic to demersal habits 

 of other gadoid fishes is apparently similar to that 

 of cod. Haddock >8 cm FL tend to eat fewer pelagic 

 organisms and prey more heavily on the benthos, 

 but the stomachs of the smallest haddock collected 

 (2 cm FL) contained some benthic animals, sug- 

 gesting a slow change from a pelagic to demersal 

 life. The same trend was noted for red hake, white 

 hake, and spotted hake. The smallest fish col- 

 lected had eaten small quantities of benthic or- 

 ganisms, but their primary food was copepods, 

 euphausiids, and chaetognaths. The larger fish 

 ( >5 cm TL) fed mostly on bottom living organisms. 

 Silver hake and pollock were rather unusual in 

 that all the fish collected had consumed large 

 quantities of euphausiids. They are less depen- 

 dent on the benthos as a food even as adults than 

 most other gadoids (Langton and Bowman 1980). 

 Because of this it is difficult to distinguish, based 

 on their diet, when they become demersal. 



Only the two flatfish, American plaice and 

 yellowtail flounder, where dependent on the ben- 

 thos as a food source at the smallest fish lengths 

 collected (3-4 cm TL). Since plaice and other 

 flatfish metamorphose early in life (most have 

 completed metamorphosis by 11 wk of age when 

 they are between 1 and 2 cm TL) they take up life 

 on the bottom at very small sizes (Hardy 1959). 

 Winter flounder, Pseudopleuronectes americanus, 

 was studied by Pearcy (1962), and it serves as a 

 typical example of how the feeding habits of the 

 flatfish change with age. He noted that the pre- 

 dominant food of metamorphosing larvae and 

 juvenile winter flounder up to 1 cm TL is copepods; 

 when the juveniles range in length from 1 to 2.5 

 cm TL, amphipods and polychaetes are their most 



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