POWLES AND MARKLE: LARVAL IDENTIFICATION 



33 



juvenile stages (as defined by completion of fin element devel- 

 opment, development of scales, etc.) are major events in fish 

 development which have been used by various authors to define 

 stages (e.g., Ahlstrom, 1968; Snyder, 1976). 



Ecological Considerations 



There are two basic ecological or zoogeographic consider- 

 ations when identifying larvae: the expected composition of the 

 larval ichthyofauna of the study area and the potential for influx 

 from "upstream" areas. 



Thorough knowledge of the adult ichthyofauna of the study 

 area is essential in order to know what larvae may occur; thus, 

 the most complete possible list of adult species is required. 

 Literature may be incomplete or erroneous, so this list should 

 be based on unpublished or personal observations as well as on 

 standard faunal works or other literature. For ease of use, the 

 list should be organized by systematic groups (e.g.. Greenwood 

 et al., 1966; Nelson, 1976). 



In addition to knowledge of the adult ichthyofauna, knowl- 

 edge of spawning seasons is central to prediction of the larval 

 fish composition. As with meristic or anatomical information, 

 published information may be incomplete so that personal col- 

 lections and unpublished information may be important. Al- 

 though capture location and season can be important in elim- 

 inating some species from consideration, caution is essential 

 here as with other "elimination" methods. 



Since most marine fishes have planktonic eggs and/or larvae 

 and many have a prolonged planktonic life the basic hydrog- 

 raphy of a study area must be understood. A "downstream" 

 study area is potentially vulnerable to an influx of larvae from 

 "upstream" spawning. In addition, the direction of "streams" 

 can differ at different depths of the water column so the influx 

 may come from more than one direction. On the shelf oR"Nova 

 Scotia the general circulation is from the northeast but there is 

 a strong influence from the Gulf Stream, both from eddies and 

 mixing which produces Slope Water. Thus, for some species, 

 the "downstream" effect comes from the northeast while for 

 tropical and oceanic species it comes from the southeast. 



Knowledge of an area's fish communities may help in inferrmg 

 which larvae may occur together— for example, an unknown 

 specimen taken together with larvae from a coastal community 



is probably not a mesopelagic species. Again, however, such 

 inferences should be considered critically. 



One sort of ecological observation may be misleading— al- 

 though spawnmg biomass may be calculated from egg and larval 

 abundance for some species, the relative apparent abundance 

 of adults is not always in proportion to the relative abundance 

 of planktonic larvae. Cryptic species may appear rare in collec- 

 tions of adults but larvae may be extremely abundant (e.g., 

 Gobiidae in tropical and subtropical waters) while species which 

 appear extremely abundant as adults may be rare as planktonic 

 larvae (e.g., the clupeid Jenkmsia lamprotaenia in the Carib- 

 bean, Powles, 1977). 



Some General Considerations 



Like larval development, identification of larvae is a dynamic 

 process— the cumulative knowledge of the student is the key to 

 accurate identification. The complexity of larval identification 

 requires that a wealth of information be applied to the task, and 

 for this reason some degree of specialization in identification of 

 larvae is required for all but the simplest identification prob- 

 lems. There are many examples of superficially similar but sys- 

 tematically very different larvae, and most students, including 

 the authors, have experienced embarrassment at an uncritical 

 identification. Identification of larvae is frequently comparative, 

 by elimination, so that wide knowledge of larval fishes as well 

 as caution are necessary. 



The student must have information of the kinds identified 

 above. Organization and ingenuity are required in order to keep 

 this information usable — card files, looseleaf binders, drawings 

 and sketches, and well-curated reference series should be de- 

 veloped or readily available. 



Finally, although many beginning students are hesitant to 

 draw, sketching and drawing (freehand, on squared paper, or 

 with camera lucida) is one of the best ways to "see" and un- 

 derstand larval anatomy. The process is painstaking and often 

 frustrating in the early stages, but will pay off in the long term 

 with increased understanding. 



(H.P.) Fisheries and Oceans, P.O. Box 15500, Quebec GIK 

 7Y7, Canada; (D.F.M.) Huntsman Marine Laboratory, 

 Brandy Cove, St. Andrews, New Brunswick, EGG 2X0 

 Canada. 



Illustrating Fish Eggs and Larvae 

 B. Y. SuMiDA, B. B. Washington and W. A. Laroche 



SCIENTIFIC illustrations of fish eggs and larvae are an in- 

 dispensible component of any descriptive work, providing 

 a visual reference of form and structure which is not possible 

 to express by written descnptions and measurements alone. 

 Illustrations facilitate identification by emphasizing distinctive 

 but often subtle morphological characters and allow for com- 

 panson of features at difl^erent developmental stages and with 

 morphologically similar taxa. These qualities make illustrations 



the preferred and most frequently used aid for taxonomic iden- 

 tification of fish eggs and larvae. 



The broad range of morphological diversity found among 

 larval fishes requires flexibility in technique and style to produce 

 eflTective illustrations, but the criteria of accuracy, clarity, and 

 consistency of style should be met. The basic concept behind 

 illustrating a fish larva involves accurately representing a three- 

 dimensional, somewhat transparent organism on a two-dimen- 



