Studies on the plasma composition offish hosts of the freshwater mussel, Hyriopsis myersiana, with implications for improvement of the medium for culture of glochidia

Abstract

Summary Analyses of several organic and inorganic elements in the plasma of different fish species in control and infested conditions with the freshwater mussel Hyriopsis (Limnoscapha) myersiana (Lea, 1856) were undertaken. The most suitable composition of plasma corresponded to the fish species which produced the highest number of transformed glochidia. The infestation assay showed that glochidia of H. myersiana had a short transformation period of 6–12 days to reach the juvenile stage. The highest recovery peak could be seen in the plasma of the common carp, with lower peaks in the nile tilapia, hybrid catfish and striped catfish. The significant increase at days 3 (P<0.05) and 6 (P3<0.01) in the free amino acids Pps, Pea, Hcy2, Cys2, Orn, Abu and Leu in plasma also seems to be related to the transformation success of glochidia. The significant decrease during both days (P<0.05 and P<0.01) in amino acids Mhis 1, Etn, Arg, Tau, Ser, Lys and potassium, magnesium and chloride in the plasma suggests an involvement with the glochidia encystment process. Conversely, the significant increase at day 12 (0.05 >P<0.0l) in Sar, Ala, tryglicerides, glucose and calcium may be related to juvenile release from the cyst. Thus, while the amino acid content of Cit, Glx, Leu, Pro, Thr and Ala in normal fish plasma influences cultured glochidia survival and transformation, an increase in concentration of the Pps-Leu group and Aad influences glochidia survival of H. myersiana during infestation. The observations suggest that a mixture of both amino acid groups in the culture medium may provide appropriate physiological conditions for H. myersiana that facilitate their transformation and survival into the early juvenile stage.