| || || Pearl oyster culture|
| || || High density rearing of Pteria penguin larvae using algal paste|
Author: Taoi, Jerome S.
Institution: University of the South Pacific.
Award: M.A. Marine Studies
Subject: Pearl oyster culture, Pearl oysters -- Growth
Call No.: Pac SH 375 .T36 2015
Copyright:10-20% of this thesis may be copied without the authors written permission
Abstract: There is a rich history of pearl oysters being cultured that goes back some 2000 years in China. Over the course of history, many new techniques were attempted to perfect the culture of round pearls and it was not until 1916 when Kokichi Mikimoto, a Japanese aquaculturalist, successfully developed the technique. Since the advent of cultured pearls by Mr. Mikimoto, much progression has been made in pearl oyster farming which has included the rearing of larvae on site. Pteria penguin, the Mabe pearl oyster, is the main species used, as the name suggests, in the culture of the Mabe pearl and it is an important oyster species in the cultured pearl industry. The rearing of this species in the high-density flow through system is the main focus of this larval rearing study. Larval rearing techniques include the static system, which has been the traditional system of rearing in many oyster farms; and the newly introduced and adapted, flow-through system. The traditional static system involves labor intensive, time-consuming procedures in the rearing of the P.penguin larvae. This system involves rearing in large tanks (up to 50 000 liters in volume) at low densities (< 10 larvae / ml), where the water is completely exchanged every 1 to 2 days. The flow-through systems, on the other hand, involve continuous water exchange (enabled by the fitting of banjo sieves), allows larval rearing densities to be increased (up to 100 larvae / mL) and tank sizes to be reduced (from 10 000 L to 250 L). Thus, it is better suited for regions that have problems with space requirements (tankage capacity for larval rearing) and high labor costs. However a major issue of concern for the flow-through system is the sieves could be clogged by the algal feed. In this study, tests were carried out at the at the Tongan mariculture facility in Sopu, Nuku’alofa, to compare larval growth (as measured by shell length) between the larvae reared in the static systems andflow-through . Average shell length (± SE) on Day 13 for the Static System Tanks (ST) larvae was 113 (± 1.85) μm compared to 90.3 (±0.73) μm for Flow-through Tank (FT) larvae, t = 3.0591, df = 38, p value = 0.004056. The larval populations in both treatments saw a steady decline, with the ST showing the highest mortality on Day 2. Larval survival at day 12 was higher for the ST with a count of 131, 250 larvae / 150 L, while FT count 2 was 97,500 larvae / 150 L. Furthermore, in this study, comparison tests on the performance of the sieve designs were carried for the Flow-through system tank at the School of Marine Studies (SMS) at University of the South Pacific, Suva, Fiji. Due to logistical constraints at the SMS aquaculture facilities, these tests were carried out using the rock oyster (Saccostrea cucullata). Larval growth comparisons for two different sieve designs were analyzed using a One–way Analysis of Variance using SPSS software version 13 (IBM Corporation, USA). It was found that on the third sampling day, the mean shell lengths using sieve design 1 (banjo sieve) were significantly greater than shell lengths using sieve design 2 (standpipe sieve), F (d.f. 1,174) = 21.431, p < 0.001. The average times until clogging for each of the four sieve sizes (32 μm, 50 μm, 75 μm, 120 μm) were compared using a One-Way ANOVA. It was observed that the larger mesh sieves clogged significantly more slowly than the small mesh sieves, (the largest mesh size of 120 μm did not clog within three days) F (df = 3, 32) = 196.38, p < 0.001. The results indicated that the standpipe sieve, also clogged significantly more slowly than the banjo sieve, F (df = 1, 32) = 7.284, p = 0.011 and that there was no significant interaction between the sieve mesh size and sieve design, F (df = 3, 32) = 2.049, p = 0.127. Finally, Constant clogging events were noticed in the banjo sieve design (treatment 1) compared to the standpipe sieves. Despite this high larval mortality was observed with the standpipe design (treatment 2 – 13,400 dead larvae). The inefficient water exchange method involved may have had a potentially deleterious effect on the larvae. While there are recommended improvements regarding sieve design and overall larvae rearing, this study has shown the potential for the assimilation of flow-through systems into hatcheries around the small island countries where space and skilled labor are the main constraints faced.The use of flow-through technology may facilitate the establishment of pearl culture industries in the Pacific region.. Keywords: Static system, Flow-through system, Pteria penguin, Saccostrea cucullata, clogging sieves, shell length, banjo sieve design, standpipe sieve design, survival, growth.