MATARESE AND SANDKNOP: EGG IDENTIFICATION 



31 



precocious fin development (caudal— exocoetids and Tricho- 

 don\ pelvic— Trachi mis), and pelvic disc development in some 

 cyclopterids (Eumicrotremus) (Fig. 14G). 



Miscellaneous characters. —The presence of a secondary mem- 

 brane inside the chorion occurs in some groups, although it is 

 lacking in most fishes. Sloniias alnvcnter eggs have a double 

 membrane (Fig. 141). These membranes occur in some of the 

 more primitive fishes including members of the Anguilliformes, 

 Clupeiformes, and Salmoniformes. In some species, like the 

 freshwater cyprinid Abbottina rivularis (Nakamura, 1969), the 

 secondary membrane is thick and gelatinous. The presence and 

 size of the micropyle are diagnostic in other fishes, particularly 

 freshwater demersal eggs (Laale, 1980; Riehl, 1980). Among 

 freshwater fishes, the cleavage pattern is important for egg iden- 

 tification. In the more primitive families (Acipenseridae, Poly- 

 odontidae, Lepisosteidae, and Amiidae), cleavage pattern is typ- 

 ically semiholoblastic as opposed to the meroblastic pattern seen 

 in the higher teleosts. Genetic studies have shown differences 

 in LDH A zymograms to be a useful, diagnostic tool for the 

 identification of Gadus morhua and Melanogrammus aeglefinus 

 eggs (Mork et al., 1983). 



Ecological and behavioral considerations.- \ number of con- 

 siderations related to mode of reproduction and collection rather 

 than the characters of the eggs themselves are essential when 

 identifying any type offish egg. In identifying demersal eggs one 

 must consider where they were collected — on rocks, on plants, 

 in masses, and if parental care is involved. Nest type, nature of 

 egg deposition, and the presence of guarding parents can all be 

 essential clues to proper identification. Also, for any egg type 



one must note spawning time (season), location depth, and gear 

 used for collection. In addition, the rearing of unknown eggs to 

 an identifiable larval stage is useful in species determination as 

 shown by Stevens and Moser (1982) for the blenny, Hypso- 

 blennius. Of course, a necessary prerequisite to accurate iden- 

 tification of eggs is a thorough knowledge of the species present 

 in any given area and their breeding seasonality. 



Summary of Characters 



Characters most useful in identification of fish eggs are the 

 following: ( I ) egg shape— spherical, ellipsoidal, irregular, or oth- 

 erwise; (2) egg size— fish eggs range in size from 0.5 to 26.0 mm; 

 (3) oil globules— presence or absence, number, size, color, po- 

 sition, and pigmentation; (4) yolk — segmented or homogeneous, 

 nature of segmentation, color, pigmentation, and circulation 

 pattern; (5) chorion— smooth or ornamented, type of ornamen- 

 tation, thickness, color, and coatings; (6) perivitelline space- 

 width; (7) embryonic characters— morphological features, pig- 

 ment patterns, and special structures; (8) miscellaneous char- 

 acters—inner or secondary membrane (presence or absence, lo- 

 cation), cleavage pattern, micropyle (size), and biochemical 

 analysis; and (9) ecological and behavioral considerations— col- 

 lection (gear, location, season, etc.), and mode of reproduction 

 (nests, parental care, etc.). 



(A. CM.) National Marine Fisheries Service, Northwest 

 AND Alaska Fisheries Center, 2725 Montlake Boule- 

 vard East, Seattle, Washington 98112; (E.M.S.) 

 Southwest Fisheries Center, P.O. Box 271, La Jolla, 

 California 92038. 



Identification of Larvae 



H. POWLES AND D. F. Markle 



MINOR errors in identification of larval fishes can lead to 

 major misinterpretations of ecological and taxonomic 

 phenomena. Fish identification and taxonomy are largely based 

 on adult characteristics and since these develop during the larval 

 period, new characters must be discovered and validated in 

 order to identify larval fishes. Usually larvae possess fewer char- 

 acters than adults and are more fragile. Identification can, there- 

 fore, be difficult and, frequently, must be based on a combi- 

 nation of character states. 



Since larval anatomy is by its nature dynamic (a given spec- 

 imen being a snapshot of the process linking embryos to adults), 

 developmental series are essential to identification. Three dif- 

 ferent approaches are used to identify larvae, the first two of 

 which arc based on developmental series: I) to raise eggs and 

 larvae from fertilized eggs of known parents; 2) to work back- 

 wards from the adult utilizing characters common to succes- 

 sively earlier ontogenetic stages; and 3) to extrapolate from pre- 



vious results obtained by (1) or (2) to synthesize generic or 

 familial diagnoses and identify by process of elimination or 

 limited corroboration (Ahlstrom in Berry and Richards, 1973; 

 Leiby, 1981). 



There are pitfalls in all approaches. Laboratory-reared larvae 

 are frequently more heavily pigmented than wild-caught spec- 

 imens and may show greater meristic variation (Lau and Shaf- 

 land, 1982). Laboratory rearing may be financially and logis- 

 tically difficult or impossible for fishes of interest. Ontogenetic 

 transformations arc based on associations of adult diagnostic 

 characters with characters that persist in progressively earlier 

 ontogenetic stages. This method requires careful attention to 

 methodology, as well as good ontogenetic series which are not 

 always available. Purely descriptive accounts of larval series 

 (laboratory-reared or reconstructed) may not be useful for iden- 

 tification purposes if no diagnostic characters that will distin- 

 guish sympatric congeners and/or similar-looking forms are pre- 



