SCIENTIA MARINA 71(3) September 2007, 421-428, Barcelona (Spain) ISSN: 0214-8358 Larval development of Dagetichthys marginatus (Soleidae) obtained from hormone-induced spawning under artificial rearing conditions ERNST F. THOMPSON 1, NADINE A. STRYDOM 2 and THOMAS HECHT 1 1 Department of Ichthyology and Fisheries Science, Rhodes University, P.O. Box 94, Grahamstown, 6139, South Africa. E-mail: [email protected] or [email protected] 2 South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown, 6140, South Africa. SUMMARY: Dagetichthys marginatus (formerly Synaptura marginata) larvae were laboratory-reared from wild caught adult broodstock as part of an aquaculture research project in temperate South Africa. A larval description for the species is provided in this paper. This work also represents the first larval description for the genus Dagetichthys, which is represent- ed by five species, three of which occur in the western Indian Ocean. Larval development in D. marginatus is typical of Soleidae. Dagetichthys marginatus larvae are heavily pigmented, with four characteristic melanophore “blotches” on the fin- fold. These larvae are easily distinguished from other soleid larvae commonly encountered in temperate South Africa based on the large size at flexion (5-7.06 mm BL) and the heavily pigmented body. Laboratory-reared postflexion larvae in this study showed similar meristic counts to those of wild caught adult fish. Despite the common occurrence of mature adults of this species in shallow marine waters off temperate South Africa, larvae are absent from nearshore ichthyoplankton catches. As yet, the spawning strategy of the species is unknown. Keywords: Synaptura, fish larvae, description, temperate ichthyoplankton, soleids, aquaculture. RESUMEN: DESARROLLO LARVARIO DE DAGETICHTHYS MARGINATUS (FAMILIA: SOLEIDAE) A PARTIR DE PUESTA INDUCIDA POR HORMONAS EN CONDICIONES DE CULTIVO ARTIFICIALES. – Las larvas de Dagetichthys marginatus (anteriormente Synaptura marginata) se cultivaron en el laboratorio a partir de adultos capturados en el medio natural como parte de un proyecto de investigación en la zona templada de Sudáfrica. En este trabajo se presenta la descripción de las larvas de esta especie. Este trabajo también representa la primera descripción del Dagetichthys, representado por cinco especies, tres de las cuales se encuentran en el Oeste del Océano Índico. El desarrollo larvario de D. marginatus es el típico de la familia Soleidae. Las lar- vas de Dagetichthys marginatus están fuertemente pigmentadas con cuatro característicos bloques de melanóforos en la aleta primordial. Estas larvas se distinguen fácilmente de otras larvas de soleidos comúnmente encontradas en la zona templada de Sudáfrica en base a su gran longitud en el estadio de flexión (5-7.06 mm BL) y a su cuerpo fuertemente pigmentado. Las larvas en estado de postflexión obtenidas en el presente cultivo mostraron similares contajes que los adultos capturados en el medio natural. A pesar de la común aparición, en aguas someras, de adultos maduros de esta especie frente a la zona tem- plada de Sudáfrica, las larvas estuvieron ausentes en las muestras de ictioplanton recolectadas en dicha zona. Hasta el momento, la estrategia de puesta de esta especie es desconocida. Palabras clave: Synaptura, larvas de peces, descripción, ictioplancton de zonas templadas, soleidos, acuicultura. INTRODUCTION life history strategy (fecundity, maturity, egg size, inter alia), good natural growth rates and an The white-margined sole, Dagetichthys mar- established, lucrative market for flatfish ginatus, was identified as a suitable candidate (Thompson, 2004). Wild broodstock were suc- species for aquaculture in South Africa, based on cessfully induced to spawn and the larvae were 422 • E.F. THOMPSON et al. reared through to metamorphosis under controlled Nothing is known about the early life history of laboratory conditions. this species prior to the allocation of this species to Dagetichthys marginatus (Boulenger, 1900), for- the genus Dagetichthys. An isolated report on egg merly Synaptura marginata (Vachon et. al., in size (2.08 mm) (Ochiai, 1966) was shown to be inac- press), is one of 56 flatfish species that occur in curate due to the misidentification of adult fish southern African waters, 16 of which are soleids (Vachon et. al., in press), while a record of three D. (Smith and Heemstra, 1986). The new soleid genus marginatus larvae (2.8-3.2 mm) (Beckley, 1986) in Dagetichthys consists of five species, three occur- temperate South Africa remains unconfirmed. The ring in the western Indian Ocean (Vachon et. al., in only information for larvae of the 14 species in the press), namely D. marginatus, D. albomaculatus genus Synaptura (Eschmeyer, 1998) was an isolated (Kaup, 1858) and D. commersonnii (Lacepède, description for Synaptura kleinii (Brownell, 1979), 1802). The distribution of Dagetichthys marginatus which was subsequently moved to the genus is listed by Heemstra and Gon (1986) as extending Synapturichthys (Heemstra and Gon, 1986). Hence from the Mozambique Channel southwards to there are no published larval descriptions for the Durban on the east coast of South Africa. However, new genus Dagetichthys. Thompson (2004) recorded the distribution of D. Laboratory rearing of D. marginatus for aqua- marginatus to extend into temperate waters as far culture provided an ideal opportunity to study and south as Gansbaai (34°35´S, 19°20´E), where it is describe larval development. Understanding the the most abundant shallow water sole species on critical changes in morphology and behaviour of intertidal and sub-tidal sandbanks. this species, as well as the timing and duration of TABLE 1. – Meristic, morphological and pigmentation (melanophore) information on soleid species occurring in South African waters for which larval descriptions are available (* denotes size at completion of flexion, while the others are size at commencement of flexion). Information provided is taken directly from literature cited (adapted from Wood, 2000). Species Myomeres (range for Vertebrae Size at Pigment Reference preflexion and flexion) flexion (mm) Austroglossus microlepis 56-58 55-57 5.2-5.5 Dorsal and ventral midline; gut; O’Toole, 1977; lower jaw; behind eyes; pectoral fins Brownell, 1979 Austroglossus pectoralis 50-58 (8-10 + 40-49) 58 3.5-3.8 Dorsal and ventral midline; fore- and Wood, 2000 hind-brain; snout; lower jaw; ventral and lateral gut; small spots on finfold Dicologossa cuneata 44-47 (9 + 35-38) 43-45 6.3-6.5 Dorsal and ventral midline; midbrain; Lagardère and hindbrain; finfold; swim bladder, Aboussouan, 1981 gut; head Heteromycteris capensis 39-41 (10 + 29-31) 40-43 6.2* Midline body contour; Three spots on Brownell, 1979 ventral finfold; ventral gut wall; lower pectoral fin margin Monochirus lutens 36-38 36-40 5 Dorsal and ventral midline; midbrain; Nichols, 1976 in posterior tail (early); finfold; ventral Olivar and Fortuño, abdominal wall 1991 Monochirus ocellatus 34-37 (8-9 + 26-28) 37-38 4 Three dorsal and two ventral concen- Palomera and Rubies, trations of small spots on finfold; caudal 1971 in Olivar and tip; dorsal and ventral body contour Fortuño, 1991 Pegusa lascaris 47 (9 + 38) 42-47 5.3 Many small melanophores scattered over Clarke, 1914 in head, body and fins. Heaviest concen Ahlstrom et al., 1984; trations over lateral and ventral gut Russell, 1976 surface and laterally on tail Synapturichthys kleini 42-45 (9-10 + 33-35) 46-47 6.5* Densely packed stellate melanophores Brownell, 1979 scattered over all body surfaces and finfold Dagetichthys marginatus 40 (preflexion) 42 5-7.6 Three distinct clusters on the dorsal and This study one on the ventral finfold and later on fins, when the last dorsal and ventral cluster fuses to form a band over the body SCI. MAR., 71(3), September 2007, 421-428. ISSN: 0214-8358 LARVAL DEVELOPMENT OF DAGETICHTHYS MARGINATUS • 423 each of these events, will facilitate larval rearing Although three successful larval batches were protocols. reared, larvae from only one spawning were used to Larval descriptions for coastal fishes are general- avoid differences in broodstock condition and thus ly lacking in South Africa (Strydom and Neira, in egg quality, which affect larval development press). Descriptions are, however, available for eight (Bromage, 1995). Ten larvae were collected at spe- of the 16 soleid species occurring on the South cific intervals representing developmental endpoints African coast (Table 1). This paper presents the first after hatching. All samples were fixed in 5% description of the early larval development of the buffered formaldehyde for 24 h and then transferred white-margined sole, D. marginatus (Boulenger, into 70% ethanol. Representatives of the larvae 1900). This information will assist in the identifica- examined and described in this paper were lodged in tion of this species in ichthyoplankton samples and the national fish collection at the South African in so doing provide much-needed information on its Institute of Aquatic Biodiversity (SAIAB 77531). spawning and its larval and juvenile distribution in All terminology pertaining to larval fishes fol- coastal waters off South Africa. lows that of Neira et al. (1998). The term “larva” was used to designate all stages in the early life his- tory from hatching to the attainment of a full fin ray MATERIALS AND METHODS complement, squamation and the subsequent loss of all larval characters, at which stage the “larva” All broodstock fish