Seasonal Fouling Stress on the Farmed Pearl Oyster, Pinctada fucata, from Southeastern Arabian Sea

Abstract

Biofouling on the periostracum of pearl oysters and on the cages has been considered as a stress factor causing mortality of the farmed stock, reducing growth rates and also affecting pearl quality. In farming experiments using the pearl oyster, Pinctada fucata, at Kollam Bay (India), biofouling was found to be a problem. This study was conducted to understand the effect of fouling on the mortality of pearl oysters kept in suspended culture, to identify the main foulers, the seasonal variation in biofouling and species successions in the community with reference to abiotic factors. The average monthly mortality rate (MR) was estimated as 0.117 ± 0.002 and the monthly variations were significantly different (P < 0.01). The total fouling (0.163 ± 0.002 g/g oyster) and biofouling weights (0.166 ± 0.007 g/g oyster) were high in December when the fouling community was composed of several species and dominated by the ascidian, Didemnum sp. December was also the period when the MRs peaked indicating that this organism was the main cause of mortality in pearl farms in Kollam Bay. A clear seasonality in the fouling community (25 species belonging to nine phyla) has been observed in the present study. On the basis of this study, monthly cleaning of oysters is advocated except during December, January, and March when the cleaning should be fortnightly.

Biofouling development and its effect on growth and reproduction of the farmed pearl oyster Pinctada margaritifera

“…Taylor et al (1997) reported that Pinctada maxima cleaned every 2-4 weeks had a better growth rate than pearl oysters cleaned every 8 or 16 weeks. Others studies also revealed a negative effect of biofouling on survival of pearl oysters (Alagarswami & Chellam, 1976;Kripa et al, 2012). The experimental set-up of these studies differed however from that of the present research; pearl oysters were reared in lantern nets or in plastic trays and epibionts were observed to overgrow the mesh, which may have, according to the authors, "prevented sufficient water flow to reach pearl oysters, thereby resulting in a lower food supply".…”

“…Several studies reporting results of the impact of biofouling on pearl oyster growth, advocated that fouling should be regularly removed to maximize growth and reduce the risk of shell deformities. Taylor et al (1997) suggested monthly removal while Kripa et al (2012) recommended monthly or fortnightly removal depending on the season. Here, we showed that despite high biofouling development, cleaning appears unnecessary as it did not improve the growth rate of pearl oysters during the period of experimentation.…”

Effect of Acetic acid treatment on the control of non-indigenous ascidians in farmed Indian pearl oyster Pinctada fucata

“…Ascidians (P. nigra, A. sydneiensis), bryozoan (B. neritina), serpulid (H. elengans), and barnacle (A. amphitrite) were the dominant communities. The study by Kripa et al (2012) recorded 25 species of foulers belonging to nine phyla and the dominant fouling community was the ascidian, Didemnum sp. in the pearl farm along southeastern Arabian Sea of India.…”

“…This is a labor intensive activity under current farming practices (de Nys and Ison, 2004). According to Taylor et al (1997) and Kripa et al (2012), the recommended time interval for cleaning of farmed pearl oyster in tropical condition is 30 days. It has been estimated that 25-30% of operational cost goes for the prevention and removal of fouling on both pearl oyster and culture equipment (de Nys and Ison, 2008).…”

“…Considerable research has been done on biofouling of farmed pearl oyster in India (Alagarswami and Chellam, 1976;Velayudhan, 1983Velayudhan, , 1987Dharmaraj et al, 1987;Kripa et al, 2012). There are no studies on the control strategies of fouling organisms.…”