Energy balance of spermatophores and sperm viability during the molt cycle in intact and bilaterally eyestalk ablated male Pacific white shrimp Litopenaeus vannamei

Abstract

The energy levels of spermatophores and sperm viability during the molt cycle were investigated in intact and bilaterally eyestalk ablated male Pacific white shrimp Litopenaeus vannamei. Sexual organs and spermatophores, expressed either as absolute weight or as a somatic index, and sperm counts were significantly higher in the ablated group. A continuous increase in the weight of the vas deferens throughout the molt cycle was observed in the ablated group but not in the control one. This suggests formation of new spermatophores in the vas deferens from the early premolt stage, negatively controlled by hormones from the X organ–sinus gland complex. Spermatophores contained the highest ATP level and adenylate energy charge (AEC), once they were visible in the terminal ampoule after ecdysis at the late postmolt stage of the first molt cycle, where it reached a mean ATP value of 3.3±0.5nmol per spermatophore in the intact group and 5.85±1.4nmol per spermatophore in the ablated group. Both groups had an AEC of ~0.73. ATP and AEC progressively decreased in both groups during the first molt cycle. At the late premolt stage, the intact group had values of ~1.6nmol per spermatophore and ~0.5 respectively, whereas the ablated group had values of ~2.9nmol per spermatophore and ~0.6, respectively. However, after ecdysis at the early postmolt stage of the second molt cycle, ATP and AEC increased in the intact group to ~2.2nmol per spermatophore and ~0.6, respectively, whereas in the ablated group, they decreased to ~1.5nmol per spermatophore and ~0.48, respectively. This differential pattern was also found for arginine phosphate, where it increased in the intact group from 24.8±7.5 to 55.2±5.5nmol per spermatophore, while it decreased in the ablated group from 78.8±10.5 to 59.6±15.5nmol per spermatophore. This suggests a cyclic molt-regulated energy balance, where new spermatophores are energy “recharged” in intact shrimp, while this process is apparently disrupted in ablated shrimp.