Tilapia Desarrollo Embrionario

Develop. Growth Differ. (2007) 49, 301– 324

doi: 10.1111/j.1440-169x.2007.00926.x

Development of the embryo, larva and early juvenile of Nile tilapia Oreochromis niloticus (Pisces: Cichlidae). Developmental staging system
Blackwell Publishing Asia

Koji Fujimura and Norihiro Okada*
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho,Midori-ku, Yokohama 226-8501, Japan

We described the developmental stages for the embryonic, larval and early juvenile periods of Nile tilapia Oreochromis niloticus to elucidate sequential events of craniofacial development. Craniofacial development of cichlids, especially differentiation and morphogenesis of the pharyngeal skeleton, progresses until about 30 days postfertilization (dpf). Becausethere is no comprehensive report describing the sequential processes of craniofacial development up to 30 dpf, we newly defined 32 stages using a numbered staging system. For embryonic development, we defined 18 stages (stages 1–18), which were grouped into seven periods named the zygote, cleavage, blastula, gastrula, segmentation, pharyngula and hatching periods. For larval development, we definedseven stages (stages 19–25), which were grouped into two periods, early larval and late larval. For juvenile development until 30 dpf, we defined seven stages (stages 26–32) in the early juvenile period. This developmental staging system for Nile tilapia O. niloticus will benefit researchers investigating skeletogenesis throughout tilapia ontogeny and will also facilitate comparative evolutionarydevelopmental biology studies of haplochromine cichlids, which comprise the species flocks of Lakes Malawi and Victoria. Key words: cichlid, craniofacial morphology, developmental stage, Nile tilapia Oreochromis niloticus.

Introduction
One of the most fundamental problems in developmental biology is the standardization of animal development. In this respect, a staging series is a usefulstandardization tool that provides accuracy in developmental studies. Work describing developmental stages has been published, not only for tetrapods (e.g. chicken, Hamburger & Hamilton 1951; frog, Nieuwkoop & Faber 1994; mouse, Theiler 1989), but also for fish (e.g. lamprey, Tahara 1988; dogfish, Ballard et al. 1993; zebrafish, Kimmel et al. 1995; rainbow trout, Ballard 1973; stickleback, Swarup 1958;medaka, Iwamatsu 2004). Developmental staging allows us to compare the developmental processes between the model species and related species to reveal underlying mechanisms of evolutionary changes among them.

*Author to whom all correspondence should be addressed. Email: nokada@bio.titech.ac.jp Received 28 November 2006; revised 24 January 2007; accepted 27 January 2007. © 2007 The Authors Journalcompilation © 2006 Japanese Society of Developmental Biologists

Cichlids (Cichlidae; Percifromes) are a family of the most successful fish among teleosts. It has been estimated that the number of their species is more than 1350 in the world (Nelson 2006). It is said that several hundred more remain undiscovered and probably exist in Africa (Turner et al. 2001). In East Africa, Lakes Victoria,Malawi and Tanganyika harbor several hundred endemic species of cichlids (Seehausen 1996; Turner et al. 2001). These cichlids are famously spectacular examples of explosive adaptive radiation and exhibit remarkable morphological, behavioral and ecological diversity (Frayer & Iles 1972). In particular, the cichlids of Lakes Malawi and Victoria, which are called haplochromine, have evolved within ashort period and thus have attracted much attention among evolutionary biologists (Kocher 2004). The haplochromine cichlids exhibit a vast diversity of feeding habits. The morphologies of the feeding apparatus, including the jaw and teeth, have surprising diversity due to adaptation to their feeding behavior (Frayer & Iles 1972; Liem 1991). Therefore, a general question is raised: How have the...