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Echinoderms are favored study organisms not only in cell and developmental biology, but also physiology, larval biology, benthic ecology, population biology and paleontology, among other fields. However, many echinoderm embryology labs are not well-equipped to continue to rear the post-embryonic stages that result. This is unfortunate, as such labs are thus unable to address many intriguing biological phenomena, related to their own cell and developmental biology studies, that emerge during larval and juvenile stages. To facilitate broader studies of post-embryonic echinoderms, we provide here our collective experience rearing these organisms, with suggestions to try and pitfalls to avoid. Furthermore, we present information on rearing larvae from small laboratory to large aquaculture scales. Finally, we review taxon-specific approaches to larval rearing through metamorphosis in each of the four most commonly-studied echinoderm classes—asteroids, echinoids, holothuroids and ophiuroids.

Summary The sea cucumber Apostichopus japonicus is an economically important species along the northwest Pacific Coast, including China, Democratic People’s Republic of Korea, Republic of Korea, Russia, and Japan. In the present chapter, we summarize knowledge on the embryonic and larval development of A. japonicus, as well as the impacts of various environmental factors on these processes. A. japonicus is a dioecious broadcast spawner. Its life cycle can be divided into eight major stages: fertilization, blastula, gastrula, auricularia, doliolaria, pentactula, juvenile, and adult. The fertilized, mainly demersal eggs measure ∼165 μm in diameter, and develop into freely rotating blastulae in 14 h at 20–21 °C. The embryos then develop into auricularia larvae over the following 34 h, at which time they gain the ability to feed. When the auriculariae grow to their maximum size of ∼800–950 μm, they shrink and transform into doliolariae, and subsequently into pentactulae after completion of metamorphosis. The development of buccal and ambulacral podia indicates the onset of the juvenile stage. It takes almost two years for A. japonicus to reach sexual maturity, and the life span of this species is commonly estimated to be at least five years. The influence of environmental factors, such as temperature, salinity, and planktic food, on larval development and growth, as well as substrate selection during metamorphosis are discussed. Transitional functions of locomotory and feeding organs in larvae, behavioral characteristics during settlement, and interindividual variations in early growth rates are also examined.

Summary The sea cucumber Apostichopus japonicus is a deposit feeder. This chapter examines its feeding biology, focusing on feeding habits, selectivity, and seasonal variation in food sources, digestive enzymes, and nutritional requirements. The influence of feed composition, including protein sources, on growth rates and metabolic and immune responses are also discussed.

Summary This chapter focuses on the gametogenic maturation and spawning of Apostichopus japonicus and explores the influence of environmental factors on gamete release. It also presents and discusses artificial spawning induction techniques. Food supply and water temperature have been identified as important mediators of gonad maturation in A. japonicus. Temperature shocks, exposure to air under shade, and exposure to running water have been used to induce spawning under laboratory conditions for the purpose of sea cucumber seedling production. In recent years, scientists have also identified other factors, such as variations in salinity, pH and light, as potential inducers of gamete release in this species.

Summary The survival of the sea cucumber Apostichopus japonicus in various land-based and field aquaculture systems is negatively correlated with the abundance of potential predators. Different predators affect the various life stages. Copepods, such as Microsetella sp. and Tigriopus japonicus , can compete for food and space with sea cucumber larvae, and they can also be predators of juveniles A. japonicus themselves) are potential predators of larvae and newly settled juveniles. Juvenile sea cucumbers with a body length 10 cm have few known predators. Various methods have been developed in an effort to protect the various life stages of A. japonicus against predators. In hatcheries and nurseries, trichlorphon can eliminate copepods without harming early life stages. In grow-on ponds and coastal areas, rocks and artificial reefs are used to provide shelter from predators. Bottom trawling, trapping, and manual removal by divers may also be used to decrease the abundance of predators in aquaculture systems.

Summary The production value of Apostichopus japonicus aquaculture surpasses that of all other marine species cultivated in China. This chapter presents the various production modes, including industrial (indoor) culture, pond (cofferdam) culture, suspended culture, and sea ranching of A. japonicus . Different facilities, production systems, techniques, and management schemes are outlined. New technologies applicable to industrial culture and novel systems developed in recent years for the culture of A. japonicus in ponds, and for stock enhancement in near-shore and off-shore areas, are also discussed. This chapter provides general guidelines and can hopefully be used as a reference for researchers or managers working on the culture and protection of A. japonicus and other sea cucumber species.

Summary This chapter provides a brief introduction to the history of consumption and fishery of the Japanese sea cucumber, Apostichopus japonicus, in the Democratic People’s Republic of Korea (i.e., North Korea). Commercial fishing of this holothurian species dates back to the early fifteenth century; collection was mainly by hand by women skin divers. Fishing intensified in the early 1900s with the introduction of SCUBA equipment, which led to a gradual decline of the wild resources. This chapter also presents information on the recent development of aquaculture programs aimed at restoring the natural resources and boosting production, both for the domestic markets and the lucrative export markets.

Publisher Summary This chapter presents several methodological considerations that are useful in determining reproductive periodicity. The oldest and most widely used quantitative method for estimating the reproductive activity is the gonad index (GI), also termed gonadosomatic index (GSI). Although not precise, the technique is particularly suitable for routinely handling large numbers of samples. The GI is calculated in several ways, but is usually defined as the ratio of the gonad wet weight to the wet weight of the body wall, test, or whole animal expressed as a percentage. Gonadal smears and/or histological sections of the gonads are widely used to estimate the reproductive status. Such data are not quantitative when the developmental cycle is merely divided into a series of maturity stages in a manner that may differ from that used by other investigators. The long-term rearing and monitoring of animals in the laboratory provides another way of assessing reproductive processes and spawning periodicities. However, compiling the data on gamete release in the laboratory constitutes a powerful tool only when the holding conditions simulate those of the natural environment.

Publisher Summary An individual gametogenic cycle usually includes the accumulation of the nutrients to be utilized during gametogenesis, the proliferation of gonial cells and their differentiation into gametes, and a reproductively quiescent or spent period when residual gametes are absorbed or the adult dies. There is often little activity in the gonads following the release of the gametes, a period sometimes termed the resting phase. The two main hypotheses have been proposed to explain the control of the gametogenic cycle within individuals: (1) it may be intrinsic, its timing being regulated by endogenous (internal) factors, and (2) it may be extrinsic or under exogenous (external) control. Gametogenesis may be staggered among different individuals during the year, so that reproduction appears to occur continuously throughout the year for the entire population. The overall length of the reproductive cycle can be regarded as a function of the rate of growth, development, and maturation of gonadal tissues ending in a spawning or series of spawnings, followed by a period of germinal redevelopment.

Publisher Summary Spawning in most species involves multiple neuro-endocrine pathways that introduce a delay between the perception of the cue and the response to it. An extreme example is the entrainment of internal rhythms by environmental cycles that eventually culminate in spawning. The timing of spawning in invertebrates is independent of prior rhythmic reproductive physiology and that some type of independent stimulus is required to induce gamete release. It might sometimes be impossible to separate the stimuli for gamete production from the actual spawning cue, since the culmination of production may itself stimulate spawning. Indeed, the identification of spawning cues is a major challenge in that it requires three types of evidence: (1) that an environmental change coincides with spawning in the field or precedes it at a fixed interval, (2) that the same change provokes animals to spawn when other conditions are maintained constant, and (3) that other factors can be eliminated as possible spawning cues. The latter point is important because numerous environmental and oceanographic factors vary in parallel. A number of methods, such as gonad indices, histology and microscopic examination of the gonads, oocyte size frequency distributions have been used with various degrees of accuracy to determine the spawning periods of echinoderms, and different interpretations of the factors that control reproduction have been proposed with more or less certainty.

Most echinoderms display seasonal or other temporal cycles of reproduction that presumably result from the complex interplay of endogenous and exogenous signals. Various environmental, chemical and hormonal factors, acting directly or indirectly, individually or in combination, have been proposed to cue, favour or modulate a suite of reproductive functions from the onset of gametogenesis to gamete release. From as early as the nineteenth century, an astonishing array of studies has been published on topics related to the control of reproduction in echinoderms, ranging from fortuitous behavioural observations to complex experimental demonstrations and molecular analyses. Although the exact pathways involved in the perception of external signals and their transduction into coordinated spawning events remain obscure for most species, significant advances have been made that shed new light on the information gathered over decades of research. By compiling the existing literature (over 1000 references), interpreting the main results, critically assessing the methodologies used and reviewing the emerging hypotheses, we endeavour to draw a clearer picture of the existing knowledge and to provide a framework for future investigation of the mechanisms that underlie reproductive strategies in echinoderms and, by extension, in other marine invertebrates.

One of the most intensively studied holothurians, Holothuria scabra has been discussed in the literature since 1833. The species is important for several reasons: (1) it is abundant and widely distributed in shallow soft-bottom habitats throughout the Indo-Pacific; (2) it has a high value on the Asian markets, where it is mainly sold as beche-de-mer; and (3) it is the only tropical holothurian species that can currently be mass produced in hatcheries. Research on H. scabra continues but because of commercial exploitation, wild stocks are declining. This review compiles data from 14 these and 352 technical reports and scientific papers pertaining to the biology, ecology, aquaculture and fisheries of H. scabra . Although several references are likely to have been missed by our investigation, we present the most complete reference list to date, including obscure material published by local institutions and/or in foreign languages. Our main aim was to summarize and critically discuss the abundant literature on this species, making it more readily accessible to all those wishing to conduct fundamental research, or aquaculture and stock enhancement programmes, on H. scabra across its entire geographic range.