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<I>Ophichthus Gomesi</I> BULLETIN OF MARINE SCIENCE. 29(3): 329-343. 1979 LEPTOCEPHALUS LARVAE OF THE EEL FAMILY OPHICHTHIDAE. I. OPHICHTHUS GOMESI CASTELNAU Mark M. Leiby ABSTRACT Two hundred fifty-five larvae of Ophichthus gomesi, comprising a developmental series from just hatched to metamorphic, are described. Osteological and morphological develop- ment is described and illustrated. A method of determining the number of adult precaudal vertebrae from the leptocephali is provided. This will allow more accuracy in leptocephalus- adult comparisons. Two morphologically distinct, premetamorphic stages of ophichthid lep- tocephali are named and described. The ubiquitous eel family Ophichthidae, long a source of confusion for ichthy- ologists (Myers and Storey, 1939; Gosline, 1950), has recently received consid- erable attention. McCosker (1977) studied intergeneric relationships based on osteology. Bohlke (pers. comm.) is preparing a manuscript on ophichthids of the western North Atlantic. The leptocephalus larvae of the family are largely un- described, however. Castle (1965) tentatively assigned 18 forms of ophichthid leptocephali from Australasian waters to genus, but was unable to provide generic definitions that could be readily applied elsewhere. Blache (1977) identifies 25 species in 14 genera from the eastern Atlantic. In the western North Atlantic two such identifications, Myrophis punctatus by Eldred (1966) and Pisodonophis cruentlfer by Richardson (1974), have been made. Fahay and Obenchain (1978) offer names for 10 additional species in 6 genera. The collection of large numbers of ophichthid leptocephali by the Florida De- partment of Natural Resources, Marine Research Laboratory (MRL), and by the Marine Biomedical Institute, Galveston, Texas (MBI), make it possible to con- tinue the identification of leptocephali with their adult forms. This paper is in- tended to be the first in a series of descriptions of ophichthid leptocephali col- lected in the Gulf of Mexico. MATERIALS Collections The 255 specimens described in this study are mainly from the MRL Pelagic Fish Series (PF) collected between December 1967 and October 1969 and from MBI collected between February 1975 and August 1976. Figure 1 shows the geographic distribution of these specimens as well as 425 more which were identified, measured and examined for developmental stage. The PF collections were made with I-m plankton nets (605 JLm with 295 /.Lmcod end). The MBI specimens were mainly taken with 2-m plankton nets (526 /.Lmor 351 JLm mesh). One specimen was taken with a 3-m Isaacs-Kidd Midwater Trawl. Size range.-The larvae ranged from 5.9 to 102.7 mm total length; eight of these are metamorphosing larvae from 90.1 to 70.5 mm total length. Presen'ation and conditioll.-Most specimens were preserved in 5% buffered Formalin. A few were preserved in 70% ethanol which proved inferior to Formalin as it resulted in wrinkled specimens. 329 330 BULLETIN OF MARINE SCIENCE, VOL. 29, NO.3, 1979 * * **•• 0: Engyodonllc Stage < 20.0mm TL .: Engyodontlc Siage ~ 20.omm TL *: Euryodontlc Stage .•• : Metamorphic Stage Figure I. Distribution of larval Ophichthus gomesi. METHODS Morphometries Measurements were taken to the nearest 0.1 mm using an optical micrometer in a binocular dissecting microscope, except where damage to the specimens precluded certain measurements. TOTALLENGTH(TL). Snout tip to caudal tip. This was used rather than stan- dard length because in late pre metamorphic and metamorphic specimens the cau- dais rays become embedded in the increasingly opaque tail tip and standard length becomes difficult to determine. PREANALLENGTH.Snout tip to anus. HEAD LENGTH(HL). Snout tip to pectoral base. PREDORSALLENGTH.Snout tip to first dorsal ray or pterygiophore in full-grown or metamorphic larvae; snout tip to anterior end of translucent dorsal thickening in which pterygiophores develop in early leptocephalus larvae. SNOUTLENGTH.Snout tip to anterior margin of clear membrane covering eye. EYE DIAMETER.Greatest horizontal distance between anterior and posterior edge of clear membrane covering eye. BODYDEPTH. Depth at deepest point; usually at anus in specimens 50 mm TL or longer; approximately midway between head and anus in specimens less than 50 mm TL. LEIBY: LEPTOCEPHALUS OPHICHTHUS GOMES! 331 \ lmm --- lmm c lmm- Figure 2. Developmental stages of larval Ophichthus gomes;: (A) Engyodontic Stage; 20.7 mm TL, (B) Euryodontic Stage; 60.5 mm TL., and (C) Metamorphic Stage; 87.4 mm TL. Meristics TOTAL MVOMERES.All myomeres including anterior ones not extending below midlateralline. PREANALMVOMERES.Myomeres back to and including one above anus. NEPHRIC MVOMERES.Myomeres back to and including one above posterior- most point of nephros. This count consistently reflects the number of precaudal vertebrae more ac- curately than do preanal myomere counts. Two closely related species of adult eels from the same geographical area may have similar total vertebral counts but may still be separated by a difference in number of precaudal or preanal vertebrae (Asano, ]962). Consequently, .it is desirable when examining leptocephali to ac- Table I. Comparison of preanal and nephric myomeres (Leptocephali) with precaudal vertebrae (adults) Preanal Nephric Precaudal Species Myomeres Source Myomeres Vertebrae Source Ahlia egmolltis 68-75 Pers. obs. 68-71 69-71 Dean, 1972 Myruphis p/atyrhYllchus 53-56 Pers. obs. 51-54 52-55 Dean, ]972 Myrophis p/umbeus 57-61 Blache, 1968 55-58 56-59 Dean, 1972 Myrophis PllllctutUS 54-59 Eldred, 1966 55-57 54-59 Dean, 1972 Anguilla rostrata 68-71 Taning, 1938 44-47 43-45 Schmidt, 1909 AI/oeonger allagoides 127 Castle, ]964 68 69 Asano, 1962 Ar;osoma ba/earieum 118-123 Blache, 1977 63-71 65-67 Blache, 1977 COllger orbigllyallus 129-140 Blache, 1977 56-61 55-56 Blache, 1977 Ophiehthus games; 67-75 pers. obs. 55-61 56-63 pers. obs. Oph;chthus pari/us 57-60 pers. obs. 51-54 46-53 pers. obs. Pythoniehthys microptha/mus 90 Blache, 1977 47-55 49-51 Blache, 1977 332 BULLETIN OF MARINE SCIENCE, VOL. 29, NO.3, 1979 curately determine the number of precaudal or preanal vertebrae in adult speci- mens. In some leptocephalus larvae the nephros terminates almost at the anus. For these species either preanal or nephric myomere counts can be used to de- termine the number of precaudal vertebrae. In cases where preanal myomeres far exceed precaudal vertebrae, the number of nephric myomeres is still an accurate indicator (Table]; Blache, ]977). PREDORSALMYOMERES.Myomeres back to and including one below first dorsal ray or pterygiophore in full-grown or metamorphic larvae; to anterior end of dorsal thickening in which pterygiophores develop in early stages. POSITIONOF GUT Loops ANDSWELLINGS.Indicated by myomere numbers at anterior and posterior edges of gut loop or swelling, or chromatophore patch which lies dorsally of each gut loop. Growth Stages Smith (1969: 385) states "there are only three stages in the pelagic life of a young eel which are qualitatively distinct": premetamorphic, metamorphosing, and glass eel. In ophichthid leptocephali I consider there to be four morphologically distinct posthatch stages: Engyodontic (Figures 2A, 3A) Commences after hatching: characterized by a few needle-like teeth, each tooth shorter than the one anterior to it; lower jaw equal to or longer than upper; nasal capsule unformed; fin-fold not yet differentiating; hypurals not forming; ratio of head and preanal lengths to total length high as compared to other stages. Euryodontic (Figures 2B, 3B, C) Engyodontic to metamorphosis: commences with shedding of needle-like teeth in anterior end of lower jaw, shedding proceeds posteriorly on lower jaw then anteriorly on upper jaw, engyodontic teeth replaced concurrently by three series of shorter, broad-based teeth in both upper and lower jaws; lower jaw becoming shorter than upper; head length as percent of total length decreasing; hypural formation and fin differentiation. Metamorphic (Figures 2C, 3D, E) Anterior and posterior nostrils formed, becoming tubular; body becoming thicker, its length and depth decreasing; head to total length ratio increasing; axial skeleton forming. Glass Eel Metamorphosis complete; adult pigmentation not yet acquired; specimens were unavailable. Osteology Thirty engyodontic to metamorphic specimens were stained differentially for bone and cartilage using a modification of Wasserburg (1976). Specimens were LEIBY: LEPTOCEPHALUS OPHICHTHUS GOM£SI 333 Table 2. Comparison of larvae examined with characters of Ophichthlls (from McCosker, 1977) (+ = present, - = absent, r = reduced, v = vertical) Character Larvae Examined Ophichthus Basibranchial #2 + +, f, - Basibranchial #3 r, - Basibranchial #4 + +, f, - Ceratobranchial #5 + + Preoperculomandibular pore #3 +,- Preoperculomandibular pore #4 Temporal pore #2 All median fins + + Tubular anterior nostril + + Supracleithrum + + Nasals + + Interopercle + + Pectoral Fin + + Precaudal Vertebrae:;; Caudal Vertebrae + + Branchiostegal Rays Free From Epihyal Angle of Suspensorium v v stained in alcian blue 2 to 4 h then rinsed and placed for 24 h in a solution of 1% KOH and aqueous alizarin red. The specimens were rinsed in distilled water, blotted and placed in consecutive solutions of four parts glycerol to six parts 1% KOH; seven parts glycerol to three parts 1% KOH; and 100% glycerol. Time in each solution was about 24 h but was largely subjective based on the appearance of a specimen. Two adult specimens were cleared and stained following Taylor (1967). Radio- graphs of 10 adults were made
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