Large-scale juvenile production of the blue crab Callinectes sapidus
Introduction
Global crab fisheries have continuously declined over the last decade (FAO, 2002). As a result, crab aquaculture gained momentum, and production technologies for different species of crabs have recently been reported (Hamasaki, 1996, Keenan and Blackshaw, 1999, Aileen et al., 2000). In addition, efforts to replenish dwindling crab populations led to the establishment of major crab hatchery programs, most notably for the blue swimming crab (Portunus pelagicus), a species for which federal and prefectural hatcheries in Japan produce in excess of 50 million juveniles per year (Takeuchi, 2000).
The blue crab, Callinectes sapidus, represents the most valuable fishery in the Chesapeake Bay and the mid-Atlantic states of Maryland, Virginia, and North Carolina, with a tristate 2001 fishery value of US$150 million. However, during the last decade, Chesapeake harvests of blue crab have declined steadily, with about a 55% drop from the 1993 record-high catches to historically low levels of 22,362 MT (49.3 million pounds) and 23,586 MT (52 million pounds) during 2001 and 2002, respectively (Blue Crab Technical Work Group Report, 2003). More alarming than the decline of the harvests is the sharp drop in the Chesapeake Bay's spawning stocks: 81% in abundance and 84% in biomass (Lipcius and Stockhausen, 2002). Consequently, larval abundance and postlarval recruitment have been reduced by an order of magnitude (Lipcius and Stockhausen, 2002). Similarly, in North Carolina's Pamlico Sound, a precipitous decline in adult abundance (down 74%), spawning stock (down 75%), young-of-the-year (down 63%), and postlarval stages (down 71%) of the blue crab has been recently observed (Etherington and Eggleston, 2000, Etherington et al., 2003). Clearly, the combination of fishing pressure and destruction of coastal nursery habitats has driven the Chesapeake and Carolina crab populations to a crisis situation.
Most strategies aimed at reversing the declining trend of blue crab populations in the Chesapeake Bay involved the regulation of fisheries and the development of sanctuaries to protect the spawning stocks (Secor et al., 2002). The above cited declines in spawning stocks and larval abundance and recruitment suggest that the blue crab population in Chesapeake Bay is severely exploited and recruitment-limited, which has driven the Chesapeake Bay to be largely below its optimal carrying capacity for C. sapidus (Lipcius and Stockhausen, 2002). This situation makes the bay's blue crab an excellent candidate for stock enhancement (Blankenship and Leber, 1995, Munro and Bell, 1997) and has led us to test the feasibility of such an approach to replenish the blue crab's severely reduced breeding stocks (Davis et al., 2004a, Davis et al., 2004c).
As a first step in studying the feasibility of blue crab stock replenishment, and also in view of developing blue crab aquaculture, we set out to establish intensive hatchery and nursery technologies for massive production of blue crab juveniles. Although such technologies were previously developed for other portunid species, in particular the blue swimming crabs, P. pelagicus and Portunus trituberculatus (Hamasaki, 2000), hatchery production of the Chesapeake blue crab has never been accomplished. This is mainly due to the complex early development process of C. sapidus. While most cultured crabs go through only five (e.g., mud crab Scylla serrata) or four (e.g., P. pelagicus) larval zoeal stages (Takeuchi, 2000, Suprayudi et al., 2002, Hamasaki, 1998), the blue crab molts through eight zoeal stages that are significantly shorter than those of the other species (Costlow and Bookhout, 1959). Multiple early life stages require more elaborate feeding and larval rearing protocols. At the end of their zoeal stage, larval crabs metamorphose into megalopae, the stage at which they develop functional claws and become highly cannibalistic (Moksnes et al., 1997). The megalopa then transforms into the early crab instar (C1 stage), which is the first postlarval stage having the body organization of the adult crab. Historically, cannibalism at the megalopa and juvenile crab stages has prevented any success in developing intensive nursery technologies for any species of crabs.
The present study describes the first successful year-round mass production of larvae and juvenile blue crab, C. sapidus, in intensive tank culture conditions.
Section snippets
Broodstock
The broodstock population consisted of 20 mature (and presumably inseminated) females (160–250 g, 15–18 cm carapace width) caught in October 2001 in the Rhode River, Chesapeake Bay, MD. The females were held in two 2-m3 round, flat-bottom tanks (22 °C; 30 ppt; constant photoperiod of 14 h light:10 h dark) during the entire year. The tanks were part of a single recirculating system (RS), which included a solid removal system and a biofilter, a protein skimmer, and an ozone treatment unit. A
Culture conditions
Water quality analysis in different tanks indicated values of less than 1 ppm for both total ammonia (NH4++NH3) and nitrite (NO2−). In cases where concentrations of these parameters were higher than 1 ppm in the open system tanks, fresh saltwater flow into the tanks was increased. DO in tanks never dropped below 90% saturation (∼6.7 ppm). Several species of organisms, which were not intentionally introduced, were present in the culture media and sediment of the tanks, including ciliates (
General
The project objectives were to gather fundamental data on large-scale blue crab production. The entire study was carried out in a totally self-contained, state-of-the-art, indoor facility specially designed for intensive shellfish and finfish production. The scope of the study was broader than many others of its kind. Typically, intensive crab production ends when crabs are at the C1–C2 stages, after which they are transferred to extensive intermediate culture or grow-out ponds (Cowan, 1981,
Summary
This study showed for the first time that blue crab (C. sapidus) juveniles could be mass-produced intensively at hatchery facilities. This could be done year-round and with a high level of efficiency compared with the other species of crabs that are known to aquaculture. During the early life stages of the blue crab (zoea 1–zoea 8), high survival rates were obtained. However, from the megalopa stage onwards, heavy losses of juveniles occurred due to cannibalism. This bottleneck, which is common
Acknowledgements
This work was supported by a NOAA award to the Blue Crab Advanced Research Consortium (Y.Z.) and funding from Phillips Seafood (Y.Z.). Anson Hines from the Smithsonian Environmental Research Center (SERC) is acknowledged for many useful discussions and advice. Alicia Young-Williams (SERC) helped in the initial culture set-up and shared her experience in maintaining adult crabs. The authors would like to thank Steven Rodgers, Eric Evans, and James Frank in COMB's Aquaculture Research Center, as
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2022, Aquaculture ReportsCitation Excerpt :It has also been reported that using higher stocking densities in rearing mud crabs does not adversely affect their growth and survival (Fielder and Heasman, 1999). Studying the hatchery production of the blue crab, Zmora et al. (2005) reported that optimum stocking density should not be determined in terms of survival, particularly when larvae are abundant, and that it is more reasonable to determine the number of megalopa per unit volume instead. Thus, the production of 3300 megalopa per 1000 L of water was found to be viable for the commercial hatchery production of S. serrata.
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2021, AquacultureCitation Excerpt :In addition, brachyurans are also robust bioindicators of anthropogenic impact (Suciu et al., 2018; Gül and Griffen, 2018). Most of these species are in the family Portunidae, such as Scylla spp. (Fazhan et al., 2017b; Waiho et al., 2018), Portunus spp. (Kunsook et al., 2014), Callinectes spp. (Zmora et al., 2005; Bembe et al., 2017) and Charybdis spp. (Sumpton, 1990; Zhang et al., 2018a); and Varunidae, such as Eriocheir spp. (Wang et al., 2016; Wang et al., 2018). Of these, the culture of brackish Scylla spp. and freshwater Eriocheir spp. are among the most successful, with a global aquaculture production of 314,099 and 778,907 t in 2019, respectively (FAO, 2021).