Thane A. Militz

Efficacy of garlic (Allium sativum) extract applied as a therapeutic immersion treatment for Neobenedenia sp. management in aquaculture

Garlic, Allium sativum L., extract administered as a therapeutic bath was shown to have antiparasitic properties towards Neobenedenia sp. (MacCallum) (Platyhelminthes: Monogenea) infecting farmed barramundi, Lates calcarifer (Bloch). The effect of garlic extract (active component allicin) immersion on Neobenedenia sp. egg development, hatching success, oncomiracidia (larvae) longevity, infection success and juvenile Neobenedenia survival was examined and compared with freshwater and formalin immersion. Garlic extract was found to significantly impede hatching success (5% ± 5%) and oncomiracidia longevity (<2 h) at allicin concentrations of 15.2 μL L(-1) , while eggs in the seawater control had >95% hatching success and mean oncomiracidia longevity of 37 ± 3 h. At much lower allicin concentrations (0.76 and 1.52 μL L(-1)), garlic extract also significantly reduced Neobenedenia infection success of L. calcarifer to 25% ± 4% and 11% ± 4%, respectively, compared with 55% ± 7% in the seawater control. Juvenile Neobenedenia attached to host fish proved to be highly resistant to allicin with 96% surviving 1-h immersion in 10 mL L(-1) (15.2 μL L(-1) allicin) of garlic extract. Allicin-containing garlic extracts show potential for development as a therapy to manage monogenean infections in intensive aquaculture with the greatest impact at the egg and larval stages.

Fish Rejections in the Marine Aquarium Trade: An Initial Case Study Raises Concern for Village-Based Fisheries

A major difficulty in managing wildlife trade is the reliance on trade data (rather than capture data) to monitor exploitation of wild populations. Collected organisms that die or are rejected before a point of sale often go unreported. For the global marine aquarium trade, identifying the loss of collected fish from rejection, prior to export, is a first step in assessing true collection levels. This study takes a detailed look at fish rejections by buyers before export using the Papua New Guinea marine aquarium fishery as a case study. Utilizing collection invoices detailing the species and quantity of fish (Actinopteri and Elasmobranchii) accepted or rejected by the exporting company it was determined that, over a six month period, 24.2% of the total fish catch reported (n = 13,886) was rejected. Of the ten most collected fish families, rejection frequency was highest for the Apogonidae (54.2%), Chaetodontidae (26.3%), and Acanthuridae (18.2%) and lowest for Labridae (6.6%) and Hemiscylliidae (0.7%). The most frequently cited reasons for rejection were fin damage (45.6% of cases), undersized fish (21.8%), and fish deemed too thin (11.1%). Despite fishers receiving feedback on invoices explaining rejections, there was no improvement in rejection frequencies over time (r = -0.33, P = 0.15) with weekly rejection frequencies being highly inconsistent (range: 2.8% to 79.4%; s = 16.3%). These findings suggest that export/import statistics can greatly underestimate collection for the marine aquarium trade as additional factors such as fisher discards, escapees, post-collection mortalities, and unregulated domestic trade would further contribute to this disparity.

Population Demographics of Tridacna noae (Röding, 1798) in New Ireland, Papua New Guinea

ABSTRACT The recent resurrection of a Tridacna maxima sensu Rosewater (1965) ecotype as a distinct species, Tridacna noae (Röding, 1798), has raised concerns that inadvertent confusion of the two species in the past may have led to overestimates of T.maxima densities and errors in determining demographic parameters. To assess the potential impacts of such a scenario, this study examined the population demographics of T. noae within the center of its geographic distribution in the Kavieng lagoonal system of New Ireland Province, Papua New Guinea. The study found that 42% of the T. maxima sensu Rosewater population could be delineated as T. noae, with T. noae being the most abundant giant clam species at 7 of the 20 study sites. Past confusion of the two species is likely to be of the greatest concern on reef sites with high or medium levels of exposure to oceanic influences where T. maxima (2.08 ± 0.41 per 400 m2, 1.86 ± 0.59 per 400 m2, respectively) and T. noae (2.06 ± 0.36 per 400 m2, 1.25 ± 0.28 per 400 m2, respectively) densities were similar (P > 0.05). In analyzing size (shell length) frequency distributions, it was determined that the T. noae population had a larger mean size (206 ± 6 mm) than that of T. maxima (161 ±6 mm, P < 0.001). Thus, in areas where the two species have overlapping distributions and fisheries regulations are based on size, reassessment of T. maxima stocks should be considered a priority given the high frequency at which the larger T. noae may comprise historical populations of T. maxima sensu Rosewater.

Embryonic and Larval Development of the Giant Clam Tridacna noae (Röding, 1798) (Cardiidae: Tridacninae)

ABSTRACT This paper reports on embryonic and larval development of the giant clam Tridacna noae. Spawning was induced by serotonin injection into the gonad. Unfertilized eggs had a mean (±SE) diameter of 101.14 ± 0.47 µm and spermatozoa heads were 8.92 ± 0.09 µmlong. Embryonic development had progressed to the 8-cell and 16-cell stages by 3 h postfertilization and to the 32-cell stage by 4 h postfertilization. Rotating gastrulae accounted for 82% of developing embryos at 9 h postfertilization. Trochophore larvae accounted for 54% of embryos at 16 h postfertilization, and 98% of larvae at 20 h postfertilization. Straighthinged (D-stage) veligers comprised 74% of developing larvae at 22 h postfertilization with mean (±SE) anteroposterior measurement (APM) of 146.32 ± 0.58 µm, dorsoventral measurement (DVM) of 118.12 ± 0.74 µm, and hinge length of 77.46 ± 0.73 µmat 24 h postfertilization. At 96 h postfertilization, 74% of veligers had settled but had retained the velum without showing development of the foot and, by 120 h postfertilization, 78% of settled veligers had become pediveligers with a probing foot. The mean (±SE) APM of pediveligers at 144 h postfertilization was 176.50 ± 0.97 µm, DVM was 151.86 ± 1.01 µm, and hinge length was 63.50 ± 0.95 µm. Gills were first observed in settled individuals 11 days after fertilization, indicating completion of metamorphosis. The methods used in this study supported successful larval culture of T. noae and provide a basis for large-scale propagation of this species.

Captive Hybridization of the Giant Clams Tridacna maxima (Röding, 1798) and Tridacna noae (Röding, 1798)

ABSTRACT The giant clam Tridacna noae is a recently resurrected taxon distinguished from Tridacna maxima on the basis of reproductive isolation, mitochondrial DNA differences, and mantle morphology and ornamentation; however, the morphological characteristics used to distinguish the two species are not consistent with genetic assignment throughout their zone of overlap. This has led to the suggestion that hybridization occurs and constituted a need to reexamine the reproductive isolation of T. noae and T. maxima. This study provides evidence that sympatric populations of T. maxima and T. noae in the center of their range overlap and can hybridize and produce juveniles. Breeding trials using T. maxima and T. noae for both maternal and paternal hybrid crosses were conducted to compare larval and early juvenile development. The fertilization success and survival of both hybrid crosses suggest potential for T. maxima and T. noae hybrids to exist in nature. On this basis, the previously reported reproductive isolation between T. maxima and T. noae may not be apposite across their zone of overlap. Future genetic, population demographic, and ecological studies should consider the possibility of hybridization between T. maxima and T. noae.