Growth performance and pathological survey on Manila clam Ruditapes phijippinarum raised on intertidal bottom and subtidal suspended net cages in Korean waters

Abstract

Previous studies have reported that recent decline in Manila clam landings in Korea is associated with degradation in the environmental qualities and increase in pathogen load， particularly the protozoan parasite Perkinsus olseni. To improve the clam landings， underwater suspended culture has recently been tried. In this study， we compared growth performance and pathology of clams raised using intertidal sowing culture (ISC) and subtidal suspended cage culture (SSCC) on the south coast. From October 2015 to May 2016， the juvenile of 23.1 mm in shell length (SL) were raised using ISC and SSCC and the growth was monitored monthly. After 2 months， increase in the somatic tissue weight in SSCC was approximately twice greater than ISC. Level of infection intensity and prevalence of P. olseni were low in both cultured clams， 3.Ox10^4±10.5x10^4 cells g tissue with the prevalence of 16.7% at IBC and 7.3x10^4±2.6x10^5 cells g tissue with 3.3% prevalence at SSCc. In January, 3 month after the culture， protozoan paramyxean parasite Marteilia sp. were found in the digestive tubules of clams in both culture areas. PCR indicated that the paraiste was Marteilia granuia，and the prevalence ranged from 62.1 to 100 % in SSCC and 16.7-96.7 % in ISC. Cumulated mortality of clams consistently increased from 1.1 % to 85.1 % in the bottom culture throughout the study. In contrast， mortality remained stable as 3.3 % for 5 months ave the clam landings， underwater suspended culture has recently been tried. In this study， we compared growth performance and pathology of clams raised using intertidal sowing culture (ISC) and subtidal suspended cage culture (SSCC) on the south coast. From October 2015 to May 2016， the juvenile of 23.1 mm in shell length (SL) were raised using ISC and SSCC and the growth was monitored monthly. After 2 months， increase in the somatic tissue weight in SSCC was approximately twice greater than ISC. Level of infection intensity and prevalence of P. olseni were low in both cultured clams， 3.Ox10^4±10.5x10^4 cells g tissue with the prevalence of 16.7% at IBC and 7.3x10^4±2.6x10^5 cells g tissue with 3.3% prevalence at SSCc. In January, 3 month after the culture， protozoan paramyxean parasite Marteilia sp. were found in the digestive tubules of clams in both culture areas. PCR indicated that the paraiste was Marteilia granuia，and the prevalence ranged from 62.1 to 100 % in SSCC and 16.7-96.7 % in ISC. Cumulated mortality of clams consistently increased from 1.1 % to 85.1 % in the bottom culture throughout the study. In contrast， mortality remained stable as 3.3 % for 5 months a