118 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



from 0.59-0.75 mm in Sardinella jussiem (Bensam, 1970) to 

 2.5-3.8 mm in Alosa sapidissima (Jones et al., 1978). Most 

 clupeid eggs are 1-2 mm in diameter. All have a segmented 

 yolk. The chorion is not ornamented or sculptured. The peri- 

 vitelline space varies in thickness among species. It may be as 

 large as 45% of the egg diameter (Sardinella zunasi) or as small 

 as 5-10% (Anodontostoma. Opisthoplerus). The egg yolk may 

 shrink relative to the egg diameter when preserved (Bensam, 

 1967) and the yolk decreases in size during the development of 

 the embryo. Oil globules are present in the eggs of most clupeids. 

 One is often present (e.g.. Sardinella. Harengula, Sardinops); 

 Escualosa thoracata has nine (Delsman, 1932a, described as 

 Clupeoides Hie). The eggs of clupeids which lay demersal adhe- 

 sive eggs (Clupea. Dorosoma, Spratelloides) have a gelatinous 

 covering around the egg. The pelagic egg of Tenualosa ilisha is 

 also covered by a gelatinous sheath. In Dorosoma petenense the 

 adhesive layer is composed of transformed ovarian follicular 

 epithelium, an unusual feature among teleosts (Shelton, 1978). 



Eggs of anchovies, family Engraididae. range in size from 0.7 

 mm (Lycengraidis) to 1.75 mm (Slolephorus, long axis). Their 

 shape varies from globular to extremely elliptical. The ratio of 

 the long axis of the ellipse to the short axis has been used to 

 identify anchovy eggs (Peterson, 1956; Phonlor, 1978). Some 

 Slolephorus species have a distinct knob on one end of the egg 

 surrounding the micropyle. A perivitelline space is present but 

 smaller and less noticeable than in clupeid eggs because of the 

 elliptical shape. Oil globules are absent except in the genera 

 Coilia and Setipinna, which have spherical eggs like clupeids, 

 and the Indo-Pacific species of Slolephorus. Fig. 58 illustrates 

 representative eggs of clupeiforms. 



Yolk-sac larvae are characterized by their size at hatching (2- 

 5 mm), which is related to yolk size; whether the yolk-sac is 

 rounded or pointed posteriorly, the number and position of oil 

 globules, number of myomeres and pigmentation. Larvae from 

 demersal adhesive eggs may hatch with pigmented eyes (Clupea 

 harengus); those from pelagic eggs hatch with unpigmented eyes. 

 Oil globules may be present in the anterior, ventral, or posterior 

 part of the yolk sac. Multiple oil globules in early embryos 

 coalesce into a single large one before hatching in Seiipinna 

 phasa (John, 1 95 1 a). A spherical yolk sac usually remains spher- 

 ical although shrinking in size during development (Sardinella 

 zunasi), while a yolk sac which is pointed posteriorly may be- 

 come more rounded as yolk is utilized (Coilia sp.). Larval clu- 

 peiforms are slender and elongate with long straight guts. Series 

 of melanophores are variously arranged above and below the 

 gut and along the ventral body wall. Subtle differences in pig- 

 mentation are very useful for identifying co-occuring larval clu- 

 peoids prior to fin development. Larvae of Engraulis mordax. 

 Sardinops sagax. and Etrumeus leres are illustrated for com- 

 parison in Moser (1981). Median dorsal melanophores in clu- 

 peid embryos migrate, reaching their characteristic ventral po- 

 sitions soon after hatching (Orion, 1 953a). In engraulids, pigment 

 cells are presumed to migrate similarly but they don't become 



pigmented until after hatching. Melanophores are commonly 

 present ventrally just anterior to the pectoral symphysis in small 

 larvae, (e.g., Opislhonema. Harengula, Engraulis, Sardinops, 

 Etrumeus). During development external rows of melanophores 

 become dark streaks and internal melanophores may increase 

 in size and number at first but disappear or become occluded 

 at transformation. A thorough description of pigment devel- 

 opment of laboratory-reared Opislhonema oglinum larvae com- 

 plete with dorsal, lateral, and ventral illustrations is given by 

 Richards et al. (1974). Preanal myomere number is taxonom- 

 ically useful but it does not correspond exactly with precaudal 

 vertebral count in the adult because of changes during trans- 

 formation. Pectoral fin buds and a continuous dorsal-caudal- 

 anal finfold are present at hatching. Fin rays first appear in the 

 caudal fin then in the dorsal, then the anal, next the pelvic, and 

 last the pectoral fin. Ossification of fin rays proceeds in the same 

 order. A full complement of fin rays is not attained until trans- 

 formation, which occurs at approximately 20 mm standard length 

 (e.g., Harengula jaguana. Houde et al., 1974; Opislhonema og- 

 linum Richards et al., 1974). Figs. 59 and 60 illustrate yolk sac 

 larvae of herrings and anchovies. 



The most useful single character for identifying larval clu- 

 peiforms is total myomere or vertebral number. Pigment pat- 

 terns are useful when vertebral counts overlap. The relative 

 positions of dorsal and anal fins and the length of the gut can 

 be used to separate clupeids from engraulids: clupeids have a 

 longer gut relative to body length and there is a gap between 

 the posterior margin of the dorsal fin and the anterior margin 

 of the anal fin; engraulids have a shorter gut and tend to have 

 the posterior margin of the dorsal over the anterior insertion of 

 the anal fin. The number of myomeres between dorsal and anal 

 fins has been used as a taxonomic character in larvae of certain 

 size classes (Houde and Fore, 1973) and in clupeid adults (Sve- 

 tovidov, 1963). During metamorphosis the position of the gut 

 and the dorsal and anal fins shift forward relative to myomere 

 number. The dorsal insertion moves 10 myomeres forward in 

 Sardinops sagax (Ahlstrom, 1968); it moves eight myomeres 

 in Harengula jaguana (Houde et al., 1974). The migration of 

 the fin takes place at approximately the time when the fin ray 

 number stabilizes. The pelvic fin migrates posleriad in Clupea 

 harengus (Lebour, 1921). Because of these dramatic changes in 

 morphology during development different characters must often 

 be used at different stages to separate species. However some 

 morphometric characters show a small but consistent difference 

 between species at all sizes as between .4losa pseudoharengus 

 and .4. aestivalis (Chambers et al., 1976). Additional care must 

 be taken when using information from laboratory-reared spec- 

 imens to identify field samples. Fin development began at 4 

 mm in laboratory-reared Opislhonema oglinum. but was not 

 observed in wild-caught larvae less than 7 mm long (Richards 

 et al., 1 974). Shrinkage due to preservation and handling (Thei- 

 lacker, 1980a) also presents problems when comparing devel- 

 opment of larvae based on length. Meristic characters in Clupea 



Fig. 58. Eggs of Clupeiformes illustrating taxonomic characters: number and size of oil globules, width of perivitelline space, degree of yolk 

 segmentation, shape, size. (A) Chirocemrus nudus. 1.56 mm. Delsman, 1923; (B) Etrumeus leres. 1.35 mm, Ahlstrom and Moser. 1980; (C) 

 Opisthoplerus tardoore, 0.85 mm, Bensam, 1967; (D) Dussumiena. 1.5 mm, Delsman, 1925; (E) .Anodontostoma chacunda. 0.92 mm, Delsman, 

 1926c; (F) Sardinops melanosticta. 1.60 mm, Mito, 1961; (G) Coilia. 1.04 mm, Delsman. 1932b; (H) Setipinna phasa. 1.10 mm, Jones and 

 Menon, 1950; (I) Anchoa mitchilli. 0.84 x 0.65, Kuntz, 1914b; (J) Engraulis mordax. 1.40 x 0.74, Bolin, 1936a; (K) Slolephorus msulans. 1.92 

 X 0.69, Delsman, 1931; (L) Slolephorus indicus or commersonii. 1.15 x 0.81, Delsman, 1931. All redrawn by J. Javech. 



