XFWS-A 599 1-26 (1970) U.S. Fish Wildl. Serv. Spec. Sci. Rep. Fish. Diagnostic Characters of Juveniles of the Shrimps Penaeus aziecus ozfecus, P. duororum cfuorarum, and P. brasiliensis (Crustacea, Decapoda,Penaeidae) SPECIAL SCIENTIFIC REPORT-FISHERIES Na 599 UNITED STATES DEPARTMENT OF THE INTERIOR U.S. FISH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES SPECIAL SCIENTIFIC REPORT- FISHERIES Robert L. Hacker, Editor Mary S. Fukuyama, Associate Editor PUBLICATIONS BOARD John A. Guinan John M. Patton, Jr. Robert L. Hacker Edward A. Schaefers John I. Hodges Parker S. Trefethen Harvey Hutchings Robert C. Wilson Leshe W. Scattergood, Chai)~man Special Scientific Report— Fisheries are preliminary or progress reports and reports on scientific investigations of restricted scope. Established as Spe- cial Scientific Reports in 1940, nos. 1-67 were issued from that date to 1949, when the new series, Special Scientific Report—Fisheries, with new serial num- bering, was started. Special Scientific Report— Fisheries are distributed free to libraries, research institutions, State agencies, and scientists. UNITED STATES DEPARTMENT OF THE INTERIOR Walter J. Hickel, Secretary Russell E. Train, Under Secretary Leslie L. Glasgow, Assistant Secretary for Fish and Wildlife, Parks, and Marine Resources Charles H. Meacham, Commissioner, U.S. FISH AND WILDLIFE SERVICE Dayton L. Alverson, Acting Director, BUREAU OF COMMERCIAL FISHERIES Diagnostic Characters of Juveniles of the Shrimps Penoeus azfecus azfecus, P. duororum duorarum, and P. brasiliensis (Crustacea, Decapoda, Penaeidae) By ISABEL PEREZ FARFANTE United States Fish and Wildlife Service Special Scientific Report-Fisheries No. 599 Washing:ton, D.C. FEBRUARY 1970 CONTENTS Page Introduction 1 Discussion 2 Identification of sex in very small juveniles 4 Distinguishing features of the rostra and dorsolateral sulci 6 Identification of taxa, males 8 Identification of taxa, females 18 Acknowledgments 26 Literature cited 26 Diagnostic Characters of Juveniles of the Shrimps Penaeus aztecus azfecus, P. duorarum duorarum, and P. brasiliensis (Crustacea, Decapoda, Penaeidaej By ISABEL PEREZ FARFANTE, Systematic Zoologist Bureau of Commercial Fisheries National Center for Systematics U.S. National Museum Washington, D.C. 20560 ABSTRACT Illustrated tables are presented for the identification and sex determination of juveniles (with carapace lengths of 8 mm. or more) of three grooved shrimps of the genus Penaetis occurring in various areas along the North American Atlantic coast, in the Gulf of Mexico, and in the Bermudas. Included is an account of the development of the petasmata, thelyca, and appendices masculinae. INTRODUCTION Many investigations have been made of juveniles of Pomeus that live in estuarine waters along the Atlantic and Gulf coasts of the United States. Particular attention has been given to their movements, habits, growth rates, and responses to fluctuations in temper- ature and salinity. Such studies are continu- ing in the United States and are now also being made along the coasts of Mexico and Central and South America; but despite the attention that has been accorded these juveniles, little progress has been made in ascertaining characteristics that will permit their identi- fication. Fortunately, the ranges of the two species of nongrooved Penaetis, P. (Litopenaeus) seti- fenis' and P. (Litopenaeus) schmitti, appar- ently do not overlap, and therefore their identi- ^ The species of Penaeus have been grouped by Perez Farfante (1969) in four subgenera, two of which are represented in American waters. The spe- cies with short adrostral sulci and a thelycum of the open type — in the western Atlantic P. setiferus and fication presents no problem; juveniles of these species having a total length of 18 mm. or more may be separated from the young grooved shrimps by the short adrostal sulci. In con- trast, the grooved Penaetis have overlapping ranges, and the juveniles are superficially so similar that identifying them has been almost impossible heretofore. The purposes of this investigation have been to study the develop- ment of the juveniles of these grooved shrimps and to discover characteristics that might al- low their specific or subspecific determination. The possibility of being able to recognize these estuarine individuals permits more reliable conclusions concerning the ecology and behav- ior of the taxa represented, and aids in at- tempts to predict the probable annual abund- ance of each of them. P. schmitti — belong to the subgenus Litopenaeus, and those species with long adrostral sulci, to Meli- certus. The three taxa treated here belong to the latter subgenus. This work is based on the examination of some 5,000 specimens collected throughout the ranges of the taxa considered. The great ma- jority of them are in the collections of the U.S. National Museum, and many are sorted according to size (carapace length). Other specimens examined are in the collections of the American Museum of Natural History; Chesapeake Biological Laboratory; Instituto Nacional de Investigaciones Biolc^gico Pesque- ras, Secretaria de Industria y Comercio de Mexi- co; Gulf Coast Research Laboratory; Museum of Comparative Zoology, Harvard University; Peabody Museum of Natural History, Yale University, and Virginia Institute of Marine Science. Burkenroad (1939) pointed out several di- agnostic features which aid in the recognition of the larger juvenile grooved shrimps from the western Atlantic, and some of these were based on secondary sexual characters. Wil- liams (1953) used the length of the adrostral sulci, characters of the rostrum, and color to identify juvenile P. (L.) sctiferus, P. (Meli- certus) d. duorarum, and P. (Melicertus) a. aztecus. The studies by Eldred (1958) on P. d. duorarum and Perez Farfante (1969) of western Atlantic Penaeus constitute the only information available on the progressive changes in the development of the thelycum and petasma of Penaeus in eastern America. The shape and length of the rostrum, the length and width of the adrostral sulci (in shrimp from the Caribbean and the Atlantic coast of South America), and the width of the dorso- lateral sulci of the sixth abdominal somite are usually helpful. In males, sternites XIII and XIV also exhibit peculiar features in some of the grooved shrimps. The most reliable char- acters for the identification of juveniles, how- ever, seem to be the structure of the petasma and thelycum. Facilitating this investigation was a pre- vious knowledge of the local occurrence of the species and the time of the year when juveniles of the three shrimps are found in estuarine waters. For instance, P. d. duorai'wm is the only one of the three that occurs in Tampa Bay; only P. a. azteciis lives north of Chesapeake Bay, and only P. d. duorarum and P. brasi- liensis frequent the waters of the Bermudas. Furthermore, P. a. aztecus juveniles first ap- pear in estuaries of North Carolina and Texas much earlier in spring than those of the other Penaeus. Finally, comparison of progressively younger specimens with those of sizes readily identifiable made possible the recognition of the earlier developmental stages. I present here a group of diagnostic char- acters that will permit identification of indi- viduals with a c.l. (carapace length — the lin- ear distance between the postorbital margin and the midposterior margin of the carapace) of as little as 8 mm., and t.l. (total length — measured from the tip of the rostrum to the tip of the telson) of about 35 mm. The typical features exhibited by each species and sub- species during a large part of the juvenile period are listed in the tables below, which are arranged in size sequences. For the rec- ognition of small individuals (less than 11 mm. c.l.), all of the characters listed should be con- sidered because occasionally one alone may not prove to be diagnostic. Figure 1 depicts the first pleopod, the post- eroventral portion of the thorax, the thelycum, and the petasma — introducing the terminology utilized in the tables. Figures 2 and 3 illustrate the characters used in the identification of sex, and the remaining figures show the peculiar characters of the rostrum, dorsolateral sulcus, and the external genitalia, as well as the pro- gressive changes in the latter, which allow the recognition of each taxon. The features cited were found to be reliable throughout the geographic range of each of the shrimps con- sidered. Whereas the carapace length at which these characters first appear may vary slightly, they are present in all individuals at the car- apace length cited. The rate of development of the petasmata and thelyca varies, conse- quently these structures do not attain the adult form when the shrimps reach a given length (e.g., 15 mm. c.l.) but rather within a definite range of lengths (e.g., 15 to 20 mm. c.l.). It seems that the range within which the external _M £ a s o u c O X 3 o genitalia of each species and subspecies attain the adult form (the animals reach the sub- adult stage) is constant, regardless of the lo- cality in which the shrimps occur. In P. a. aztecus the petasma and the thely- cum often develop at a slower pace, relative to body length, than in the sympatric P. d. duo- rarum. For each length listed, I have compared the more advance representatives of P. a. aztecus with the least advanced members (i.e.. least developed genitalia) of P. d. duorarum, and the differences presented herein seem to be valid. Although there are still no infallible cri- teria on which recognition of every single ju- venile under 10 mm. c.l. may be based (for instance, it is difficult to distinguish females of P. brasiliensis from females of the sjTnpatric P. d. duorarum) , the characters cited here al- low the identification of many small and prac- tically all larger juveniles. IDENTIFICATION OF SEX IN VERY SMALL JUVENILES In individuals as small as 4 mm. c.l., about 18 mm. t.l., sex in the three taxa can be de- termined by the position and size of the endopod of the first pair of pleopods. The endopod in males is located more proximally on the basis and is a little longer than in females (figs. 2 and 3). Also, in males of that length, sternite XIV bears a posteromesial ridge (figs. 4a and 5a), whereas in females sternite XIV is rather evenly produced to a central elevation (figs. 4b and 5b). L 0-5 mm. Figure 2.—Penaeus aztecus aztecus. Anterior (dorsal) view of endopod of first right pleopod. a. $ 5.5 mm. C.I., White Oak River, N.C. b. 9 5.5 mm. c.l., Missbsippi Sound, Miss. Figure 3.—Penaeus duorarum duorarum. Anterior (dor- sal) view of endopod of first right pleopod. a. ^ 4 mm. c.l., Mississippi Sound, Miss, b, 9 4 mm. C.I., Mississippi Sound, Miss. Of o oc O Q Z < < I- o ILI X I— O UJ 3 -a u P4 oli >. 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