Interpretation of statolith microstructure in reared hatchling paralarvae of the squid Illex argentinus

Abstract

To identify sub-daily or aperiodic increments of statolith growth in the ommastrephid squid Illex argentinus, we examined statolith microstructure, especially with regard to the natal ring, where counting of daily growth increments should begin, and the widths of subsequent daily increments. Paralarvae obtained by artificial fertilisation were incubated on board at different temperatures ranging from 11.4 to 25.4°C, and were starved throughout the experiments. We observed statolith growth from newly hatched to 10-day-old paralarvae and used alizarine complexone staining to attempt validation of the growth. The maximum statolith radius (MSR) of newly hatched paralarvae was constant at 21.1 μm across the full range of temperatures, with the exception of 25.4°C. Daily growth of MSR was analysed separately in two phases, the pre-yolk-absorption phase (i.e. yolk sac still present) and the post-yolk-absorption phase. During the pre-yolk-absorption phase, the daily growth rate (DGR, y) of the MSR varied from 3 to 7 μm day–1 depending on rearing temperature (x) and was expressed as y = 0.37x – 1.77. We concluded that the natal ring forms at 21 μm MSR. The initial increment width obtained from the DGR of MSR seems applicable for distinguishing daily rings from sub-daily rings, although this application should be limited to hatchling paralarvae in the pre-yolk-absorption phase.

Abiotic influences on embryo growth: statoliths as experimental tools in the squid early life history

“…The statolith growth rates of these individuals are the slowest recorded during the first two months of culture (Villanueva 2000a). Similarly, statolith growth rates after yolk absorption are slower than rates during the yolk absorption period in the oceanic ommastrephid squid Illex argentinus starved under laboratory conditions (Sakai et al 2004). Thus, the growth rate of the squid statolith during the first few days after hatching seems to record the transition from the endogenous to exogenous feeding periods which is evident in somatic growth rates.…”

“…In the past the effect of temperature on cephalopod embryonic and post-hatch growth within the characteristic temperature range for each species has been the focus for experiments (Durholtz and Lipinski 2000;Villanueva 2000a, b;Villanueva et al 2003;Sakai et al 2004). A well described inverse relationship exists between temperature and the rate of embryonic development and growth (Boletzky 1987).…”

Useful Techniques for Artificial Fertilization of the Ommastrephid Squid Illex argentinus

“…Chorion diameter increased markedly during the third chorionic expansion (stages [17][18][19][20][21] and coincided with an increase in embryonic BL (Fig. 5-a).…”

“…Artificial fertilization techniques are useful for producing squid embryos and hatchlings to study the early life history of oceanic ommastrephid species, as these are generally difficult to collect during normal capture surveys, e.g., Illex illecebrosus 14 , Todarodes pacificus 20,23 , Ommastrephes bartramii 19 , Sthenoteuthis oualaniensis 19 , I. argentinus [16][17][18] , and Dosidicus gigas 22,24 . However, except for T. pacificus, I. illecebrosus, and I. argentinus, the technical constraints associated with conducting experiments at sea have meant that accurate information on the fundamental characteristics of embryonic development and hatching stages of most of these species is not known.…”

Cephalopod growth: historical context and future directions

“…Sakai et al (2004) provide useful and fresh insight into statolith increment periodicity and formation for Illex argentinus hatchlings grown under different temperatures. This paper is exciting because the researchers used a combination of cutting-edge techniques/technologies (artificial fertilisation, ship-board incubation at different temperatures, and staining of statoliths with alizarine complexone) to reveal patterns of increment periodicity.…”