Changes of gonadal morphology and mRNA expression patterns of vitellogenin were investigated in Siberian sturgeon Acipenser baerii (Chondrostei) during its early gonadal maturation period. Early differentiations and morphological transitions of both ovaries and testes appeared to occur actively until the age of 3 years, however from then on, the maturation patterns to full maturity were largely gender-dependent, in which males showed a faster progression of maturation than did females while females experienced a steady-state progress with a lagged interval before entering the final maturation. Expression of vitellogenin mRNAs are closely correlated with transitional patterns of gonadal appearances. In both females and males, hepatic mRNA levels of vitellogenin exponentially increased in the earliest interval (up to 1-year-old). However, in subsequent periods, vitellogenin expression in females continued to increase with age, whereas in males, the expression stabilized at a younger age. Nevertheless, at the age older than or equal to 7-year-old, fully matured individuals showed a quite low level of vitellogenin expression in both females and males. Collectively, results from this study could be useful as a fundamental guideline to address the gonad maturation of this sturgeon species, which is helpful for making practical decisions about farming practices and management for caviar production on local sturgeon farms.

Behavioral response to a diel photoperiodicity (500 lx for 16 h, 5 lx for 4 h and < 0.5 lx for 4 h) and phototactic characteristics in dark conditions were examined with Siberian sturgeon Acipenser baerii (Chondrostei, Actinopterygii) prelarvae. Siberian sturgeon prelarvae represented both qualitative and quantitative changes in their behavioral patterns according to different light intensities in a diel photoperiodicity. Under daylight conditions (500 lx), prelarvae displayed saltatory changes of behavioral features with ages (Day 0-Day 9) in a general order of swimming-up/drifting, swimming in the upper water column, benthic swimming with rheotaxis, schooling and postschooling behavior. Compared to daylight conditions, prelarvae tended to show more benthic performances and quantitative reductions of schooling and postschooling behaviors under dimlight conditions (5 lx). Under dark conditions (< 0.5 lx), prelarvae exhibited a fairly uniform behavioral pattern characterized by the benthic swimming across the bottom of the tank. From phototaxis tests under dark conditions, navigational responses of prelarvae to a spotlight illumination were quantitatively changed as their ages increased. The phototactic responses reached the peak on Day 2, continued until Day 4, and then gradually decreased until Day 8. A partial recovery of positive phototaxis was observed on Day 9. Data from this study suggest that the diel light cycle as well as the light intensity of each interval in the cycle should be considered as important components of a practical guide for evaluating fitness and developmental states of artificially propagated Siberian sturgeon prelarvae.

Karyotype analysis is a major work in the process of triploid abalone production for the purpose of productivity and quality improvement. However, the metaphase spreads for karyotype analysis have been prepared just from the larvae at trochophore stage, which has restricted the spectrum of sample correction inhibiting more efficient analysis. Here, we investigated the feasibility of preparing metaphase spreads from the larvae at veliger stage that is the next developmental stage of trochophore. For this, diploid and triploid larvae at trochophore and veliger stages from Pacific abalone (Haliotis discus hannai ) were subjected to metaphase spread preparation and its efficiencies were measured and compared each other. As the results, although the efficiencies of metaphase spread preparation were significantly lower in the larvae at veliger stage compared to the ones at trochophore stage regardless of ploidy status, we found that the preparation of metaphase spreads, which showed the clear chromosomal images containing the normal number of chromosomes, was possible from the veliger stage larvae. On the other hands, all larvae used in this study regardless of developmental stage and ploidy did not show colchicine sensitivity. Moreover, no significant difference was observed in cell cycle distribution of the cells comprising larvae between two developmental stages regardless of ploidy status. These suggested that the details of protocol to prepare metaphase spreads from abalone larvae should be optimized depending on its developmental stages. Taken together, we demonstrated the feasibility of preparing metaphase spreads from H. discus hannai veliger stage larvae for karyotype analysis.

Potential utility of 14 candidate housekeeping genes as normalization reference for RT-qPCR analysis with developmental samples (fertilized eggs to late veliger larvae) in Pacific abalone Haliotis discus hannai was evaluated using four different statistical algorithms (geNorm, NormFinder, BestKeeper and comparative ΔCT method). Different algorithms identified different genes as the best candidates, and geometric mean-based final ranking from the most to the least stable expression was as follow: RPL5, RPL4, RPS18, RPL8, RPL7, UBE2, RPL7A, GAPDH, RPL36, PPIB, EF1A, ACTB and B-TU. The findings were further validated via relative quantification of metallothionein (MT) transcripts using the stable and unstable reference genes, and expression levels of MT were greatly influenced according to the choice of reference genes. In overall, our data suggest that RPL5 and RPS18, either singly or in combination, are appropriate for normalizing gene expression in developmental samples of this abalone species, whereas ACTB, B-TU and EF1A are less stable and not recommended. In addition, our findings propose that standard deviations in geometric ranking as well as geometric mean itself should also be taken into account for the final selection of reference gene(s). This study could be a useful basis to facilitate the generation of accurate and reliable RT-qPCR data with developmental samples in this abalone species.