58 MARCH 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Strip spawning of shellfish, such as the Eastern oyster Crassostrea virginica, is labor intensive, inasmuch as each oyster must be handled. For example, at the New Jersey Aquaculture Innovation Center (AIC) at Rutgers University in Cape May, where millions of oyster seed are produced in a season, 150 oysters may be used for a single spawning event and six or more people may be involved in opening oysters and stripping gametes. Unlike oysters, bivalves such as the hard clam Mercenaria mercenaria cannot be strip-spawned (Utting and Spencer 1991). Spawning of hard clams is even more timeconsuming because temperature must be manipulated over time to trigger spawning in at least one individual, with some uncertainty that this induces others to follow (Davis and Chanley 1956, Ansell 1967, Gallager and Mann 1986, Helm et al. 2004). For some non-commercial bivalve species, it is not yet known if they can be reliably stripspawned. The non-edible ribbed mussel Geukensia demissa, which is being tested in projects designed to stabilize living shorelines (Kreeger 2011), is an example. Other consequences of strip-spawning include loss of broodstock and inclusion of under-ripe eggs in the spawn. When an animal is opened for strip-spawning, future spawns are not possible, regardless of use of gametes. For expensive broodstock, such as special genetic lines, including polyploid animals, this is a high cost. Moreover, if the offspring of a particular animal does well, the option to spawn the same broodstock again is lost. Regarding gamete quality, eggs are usually a mixture of ripe and unripe (DeBrosse and Allen 1991). Naturally spawned eggs are sufficiently ripe to produce viable larvae. Many small-scale operations also have space limitations. This paper describes an inexpensive, low-labor, broodstock-preserving, The Bin-Silo System: A Simple Spawning Method for Bivalve Shellfish Brenda J. Landau minimal-space method for spawning bivalves called the bin-silo method, so named for the main components of the system. The bin-silo method represents an alternative to traditional spawning methods. In general, traditional methods are higher cost with a more predictable outcome than the bin-silo method. If the bin-silo method does not result in larvae from an attempted trial, nothing is lost, except a few hours of time over a twoday period, and the user can immediately restart the bin-silo with different broodstock. The bin-silo spawning method should become more reliable over time as culturists adapt the system to their circumstances. The Bin-Silo System The basic components of the system consist of a silo1, which is a bucket-like container with a mesh bottom. The mesh size at the bottom of the silo must be sufficient to retain broodstock shellfish. A silo with broodstock is placed inside a larger (200-L) bin2 containing water heated to 26-28 C (Fig. 1). The heater is then turned off and the water temperature is allowed to return to ambient conditions. The brief and mild temperature shock is intended to trigger spawning. After spawning, gametes must be separated from actively filter-feeding broodstock, lest they be removed from the combined culture. An airlift pump gently circulates water between bin and silo (Fig. 2). The vertical circulation also carries gametes and larvae. Eggs and larvae are slightly denser than seawater and will sink. Placement of the airlift intake above the bottom of the bin allows collection of larvae in a quiescent zone FIGURE 2. An airlift pump creates vertical water circulation in the bin-silo that carries gametes through the mesh retaining the broodstock at the bottom of the silo. Embryos eventually sink below the level of the airlift intake and are thus removed from circulation. Black lines outline the bin, silo and crossbar that supports the silo. The red line marks air tubing that connects the airlift pump to an aquarium air blower. Blue dots and arrows indicate the flow of air and water through the airlift riser. FIGURE 1. The bin-silo system. The silo containing shellfish broodstock fits inside the bin, supported by the crossbar at the top.
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