Possibility of self-fertilization during hatchery culturing of giant clam, Tridacna crocea

Abstract

Giant clams are simultaneous hermaphrodites and are assumed to ejaculate first and, after completely stopping ejaculation, release eggs. In the seed production method aimed at preventing self-fertilization, each adult clam is induced to ejaculate in a tank and then release eggs in another tank. Giant clams, however, have recently been suggested to continue ejaculation for a period after the beginning of egg release. The overlap between ejaculation and egg release might lead to self-fertilization in the tank used for egg release, especially for the eggs released just at the beginning of spawning. We examined the possibility of such self-fertilization for the giant clam Tridacna crocea and obtained three results. (1) In observations with the naked eye in a laboratory, 2 of 38 T. crocea simultaneously ejaculated and released eggs. (2) In a laboratory experiment, 1.5 to 80.0% of eggs released from each adult clam developed into D-shaped larvae without artificial cross-fertilization. Such development occurred more frequently for the eggs released earlier from each adult clam than for the eggs released later from the clam. (3) In observations at a hatchery, 2 to 94% of the eggs released from 4 of 5 adults were found to develop into D-shaped larvae without artificial cross-fertilization. The three results suggest that at least some T. crocea adults continue ejaculation for a period after starting spawning eggs, which causes self-fertilization.

Microsatellite variation of mussels (Mytilus galloprovincialis) in central and eastern Mediterranean: genetic panmixia in the Aegean and the Ionian Seas

“…Self-fertilization during spawning constitutes a phenomenon closely related to inbreeding, which could explain heterozygote deficiencies, and it has been noted in several aquatic invertebrates, including clam shrimp (Chasnov, 2010), scallops (Martinez et al, 2007) and clams (Kurihara, 2010). In mussels, hermaphroditism has been reported at very low prevalences, although it is likely to be increased when they are exposed to toxic chemicals (Ortiz-Zarragoitia & Cajaraville, 2010).…”

Probability of Symbiosis Establishment by Giant Clams with Fresh and CulturedSymbiodiniumIsolated from Various Host Animals

“…Near the station, adult giant clams Tridacna crocea (shell length, 80.0-132.1 mm ) and Tridacna maxima (shell length, 100.9-182.2 mm) were collected and kept for ;0.5 y in tanks with running seawater. The clams were stimulated to spawn sperm and eggs in the tanks from June to October between 2008 and 2010 using the technique in Kurihara et al (2010Kurihara et al ( , 2011. The eggs were crossed with the sperm and were moved to other tanks containing seawater that had been filtered through sand and anthracite.…”

Impediment to Symbiosis Establishment between Giant Clams and Symbiodinium Algae Due to Sterilization of Seawater

“…These seeds were produced from artificially fertilized eggs (see [24] and [25] for details) and were moved into tanks (volume of seawater: 3 to 30 metric tons) at densities of 0.2 to 0.85/ml on Day 1. The number of seeds moved into tanks were estimated from the volume of seawater in the tanks and the density of seeds.…”