TECHNIQUES AND APPROACHES 



Early Life History Descriptions 

 E. M. Sandknop, B. Y. Sumida and H. G. Moser 



FISHERIES studies require accurate identification of subject 

 species. Identification of the developmental stages of fishes 

 is complicated by the small size of the specimens, their fragility, 

 and the relatively great changes in their structure and pigmen- 

 tation. Experience has shown that major changes can occur over 

 very small growth increments and these can only be documented 

 by a continuous growth series. Published descriptions of de- 

 velopmental series vary in quality, perhaps more than do species 

 descriptions of adults. Prior to Bertelsen (1951) and Ahlstrom 

 and Ball (1954), most published descriptions were based on 

 relatively few specimens, which were described individually. In 

 their study of the early life history stages of the jack mackerel 

 (Trachunts syinmetricus), Ahlstrom and Ball (1954) used over 

 500 eggs and a series of about 250 larvae, transforming speci- 

 mens, and juveniles to describe development. Changes in struc- 

 ture and pigmentation were thus described as a dynamic con- 

 tinuum, with emphasis on variation, in contrast to the approach 

 of most previous workers. Developmental osteology was con- 

 sidered an integral part of the description as were seasonal and 

 geographic distributions of eggs and larvae. This paper was fol- 

 lowed by several others (Ahlstrom and Counts, 1955, 1958; 

 Uchida et al., 1958; Kramer, 1960) and these became models 

 for subsequent descriptive papers, including some which treated 

 several species in various taxonomic groups (Moser and Ahl- 

 strom, 1970; Ahlstrom, 1974; Ahlstrom et al., 1976; Moser et 

 al., 1977; Kendall, 1979; Brownell, 1979; Richardson and 

 Washington, 1980; Fahay, 1983; Leis and Rennis, 1983). The 

 following is a brief account of the elements involved in preparing 

 early life history accounts of teleosts. 



Sources 



The major source of material is plankton collections. Typical 

 survey tows strain a column of water 200 m to the surface and 

 sample eggs and subsequent larval stages of a major portion of 

 the fish fauna (Smith and Richardson, 1 977). Fishes which have 

 highly stratified vertical distributions are undersampled by 

 oblique tows and require special gear or tow strategies. For 

 example, surface dwellers can be sampled by neuston nets (Zait- 

 sev, 1970; Nellen and Hempel, 1970; Hempel and Weikert, 

 1972; Nellen, 1973a; Ahlstrom and Stevens, 1976) and those 

 species residing near the bottom may be sampled by epi-benthic 

 plankton nets (Schlotterbeck and Connally, 1 982). Larger larvae 

 and transforming stages are poorly sampled by typical survey 

 tows principally because of accumulated mortality, increased 

 avoidance capacity, and migration out of the sampling zone. 

 These stages are more effectively sampled by trawls (Tranter, 

 1968), dip-netting with attractor lights (Klawe, 1 960), light traps 

 (Faber, 1982), and fish predators (Haedrich and Nielsen, 1966). 

 Recently, scuba divers have collected oceanic larvae with their 

 delicate structures intact (Harbison et al., 1978; Govoni et al., 

 1 984). Developmental series may also be obtained by rearing 



larvae from eggs collected at sea or from captive brood stock 

 (Houdeetal., 1970, 1974; Houde and Swanson, 1975; Richards 

 etal., 1974; Houde and Potthoff, 1976; Moser and Butler, 1981). 

 This method becomes essential when working with speciose 

 faunas (e.g., Sebastes, warm water shorefishes), if only to de- 

 termine which species cannot be identified. 



Use of Specimens 



The characters and techniques used in identifying develop- 

 mental stages are discussed elsewhere in this volume (see Ken- 

 dall et al.; Matarese and Sandknop; Powles and MarkJe). From 

 the continuous developmental series two subseries are assem- 

 bled and these form the basis for the description. The first series 

 is used to describe morphology and pigmentation. Specimens 

 in the second series are cleared and stained by a variety of 

 techniques to describe the development of cartilaginous and 

 osseus features (Potthoff, this volume). 



The number of specimens used to construct these series is 

 dependent on several factors: 1) specimen availability, 2) length 

 (duration) of the development period, and 3) complexity of 

 developmental change. A guideline is that there should be enough 

 specimens to demonstrate the beginning, progression and com- 

 pletion of significant developmental changes in morphology and 

 pigmentation. Usually more specimens are required for species 

 which have extended larval periods; however, many fishes which 

 transform at small sizes undergo great change over small length 

 intervals. For example, lined sole {Achirus lineatus) hatch at 1 .6 

 mm, transform at about 4.0 mm, and complete a large suite of 

 developmental changes over a 2.5 mm length interval (Houde 

 et al., 1 970). The majority of marine teleosts transform between 

 10 and 30 mm and, for these, major developmental events can 

 be documented by specimen length increments of 0.5-1.0 mm. 

 Multiple samples representing 1 mm-intervals are required to 

 study fine-scale character variation; however, such studies have 

 rarely been done (Ahlstrom and Moser, 1981). 



A table of morphometric measurements constructed from the 

 unstained series provides data on the size at important devel- 

 opmental milestones (e.g., hatching, notochord flexion, fin for- 

 mation, transformation) and provides a basis for analyzing 

 structural change and allometric growth. These specimens can 

 be used to construct character matrices of complex or diagnostic 

 pigment changes. Illustration specimens chosen from the series 

 provide an integrated view of major characters and also, if ac- 

 curately executed, are themselves morphometric and meristic 

 documents (Sumida et al., this volume). 



The stained series is used to construct a meristic table that 

 forms the basis for following the development of fin rays and 

 supporting elements, the axial skeleton and cranial bones (Dunn, 

 this volume). Fine bony structures, such as cranial spines are 

 also apparent in these preparations. 



Published descriptions employing these basic elements are 



23 



