20 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 11. Liopropoma sp., 11.0 mm. Collected by G. R. Harbison, 

 16 May 1981, 6°31.8'S, 150°21.8'E. Note elongate dorsal spines. 



of contraction of melanophores are not well understood al- 

 though they may be partially related to ambient light intensity. 

 The relative size and placement of melanophores are genetically 

 determined and therefore useful in a systematic context, while 

 the degree of contraction seems to be physiologically deter- 

 mined. 

 In general, the body shape and size at various stages of de- 



velopment are characteristic of larvae at the generic or familial 

 level, although subtle differences in body shape may be char- 

 acteristic of species. Size at stage of development can be envi- 

 ronmentally modified (e.g., by temperature or food) to some 

 extent, but is primarily genetically determined. There appears 

 to be some convergence in larval body shape, such as on a long 

 tubular body in several divergent groups (e.g., Clupeiformes, 

 Argentinidae, Blennioidea), just as there is on the "herring" 

 morph of adults. 



A valuable and fairly widespread set of larval characters con- 

 cerns the development of spines and armature on bones of the 

 head and cleithral region. Such armature has provided diag- 

 nostic larval characters as well as material for systematic infer- 

 ence at levels from species to order. Larval head armature ap- 

 pears to be a mark of the Acanthopterygii. Only a few scat- 

 tered examples of such armature appear in fishes which have 

 only soft rays as adults (e.g., Sudis). Within the spiny-rayed 

 fishes, beryciforms are quite heavily armed with spines on many 

 head bones. Perciforms usually do not have spines on the pa- 

 rietals but the supraoccipital is armed in some. The Scorpaeni- 

 formes are just the opposite: they tend to have head armature 

 that includes spines on the parietals but do not have spines on 

 the supraoccipital. 



Nowhere are larval specializations more evident or varied 

 than in the fins. Elongation of particular spines or soft rays or 

 enlargement of whole fins are frequently seen. Such elongations 

 have been described for rays of the dorsal, pelvic, pectoral, and 

 caudal fins; thus they occur with both spines and soft rays. In 

 some, these long rays may bear pigmented "bulbs" or appear 

 like flagellae. Such specialized rays are produced in the dorsal, 

 pectoral, or pelvic fins of taxonomically diverse fishes. The ex- 

 tended gut of "exlerilium" ophidioid larvae (Fraser and Smith, 

 1974) and the serial pigment pattern of some leptocephali (Smith, 

 1979) may give the same appearance to potential predators as 

 these elongate rays. All of these structures may be mimicking 

 siphonophores: a remarkable example of convergence (Fig. 10 

 and 1 1 ). Elongate fin spines are heavy and armed with serrations 

 in some. Elongated rays are often precocious in development, 

 with some even forming in the egg. These fin characters seem 

 to vary at the family-species levels. Other characters associated 

 with fin development include the sequence of formation and 

 movement and loss of whole fins or some of the rays. Dorsal 

 and anal fins move forward along the body during larval de- 

 velopment in elopiform and clupeiform fishes. They develop in 

 "streamers" in the finfold of argentinoids and attach to the body 

 proper just before or during transformation. The shape of the 

 finfold, presence or absence of a preanal finfold, and shape of 

 the pectoral fin base provide additional characters at the family- 

 genus level. 



Gut characters offish larvae include length and shape as well 

 as the development of a protruding, trailing hindgut in some. 

 In fishes with pholophores, their placement and sequence of 

 development are excellent characters at the subfamily-species 

 levels. The eye of a larva is specialized in a number of ways. 



Fig. 12. Examples of special juvenile stages. (A) Hexagrammos lagocephalus. 28.0 mm. A neustonic or epipelagic form of a species that is 

 demersal as an adult (from Kendall and Vinter, 1984); (B) Forapiger longirosths. 17 mm. A spiny form that lives on tropical reefs as an adult 

 (from Kendall and Goldsborough, 1 9 1 1 ); (C) Sehaslolobus altivetis, 26.8 mm. A barred pelagic form of a species that is demersal on the continental 

 slope as an adult (from Moser et al., 1977); (D) Oncorhynchus kisulch. 37 mm. The freshwater alevin or parr stage of an andromous salmonid 

 (from Auer, 1982); and (E) Kali macrodon. 45 mm. The juvenile of a bathypelagic species. Originally described as Gargaropteron pterodactylops 

 (see Johnson and Cohen, 1974). 



