[Exogenous Sr2+ sedimentation on otolith of chum salmon embryos].

To explore the exogenous Sr2+ sedimentation on otolith of chum salmon embryos, chum salmon embryos were exposed to culture water contained Sr2+ at Sr2+ concentration of 50, 100, 200 or 400 mg . L-1 for 48 h to imitate Sr2+ sedimentation. After a culturing period of 12 d and 100 d, the otoliths of the chum salmon were taken to detect exogenous Sr2+ sedimentation with electro-probe microanalyzer (EPMA). The results showed that obvious deep red strontium signatures were produced in the otolith of chum salmon at different concentrations of Sr2+. The mean and extreme values of peak strontium area were not stable for the same Sr2+ dose, but the lowest of all the peak values was 35.1 times as much as that of control. Overall, the strontium value increased with the increase of Sr2+concentration. The strontium peak had no signs of abating after a culture period of 100 d. The results also showed that strontium was gradually deposited in the otolith, and had obvious hysteresis to immersion. Strontium sedimentation could also return to a normal level after the peak. These characteristics accorded exactly with the requirement of discharge tag technology, which indicated that exogenous Sr2+ was suitable in the marking of salmon otolith.

Effect of treatment of chum salmon Oncorhynchus keta (Walbaum) eggs with 1,3;1,6-ß-D-glucans on their development and susceptibility to Saprolegnia infection.

The effects of six 1,3;1,6-ß-D-glucooligo- and polysaccharides with different structures (ranging from 1 to 10 kDa in molecular mass and containing 10-25% of ß-1,6-linked glucose residues) from brown algae, Saccharina cichorioides, on development of the chum salmon, Oncorhynchus keta (Walbaum), were evaluated. Exposure of chum salmon eggs to 1,3;1,6-ß-D-glucans with a molecular mass of more than 2 kDa increased the survival of embryos and juveniles and their resistance to Saprolegnia infection by up to 2.5-fold, leading to a weight gain in juveniles of 40-55% compared with The control chum salmons. The 1,3;1,6-ß-D-glucans with molecular mass of 6-8 kDa and used at a at concentration of 0.5 mg mL(-1) rendered the best stimulative effect.

Embryonic and post-embryonic expression of arylalkylamine N-acetyltransferase and melatonin receptor genes in the eye and brain of chum salmon (Oncorhynchus keta).

Melatonin and arylalkylamine N-acetyltransferase (AANAT), the rate-limiting enzyme in melatonin synthesis, have taken on special importance in vertebrate circadian biology. Recent identification of genes encoding two AANAT (AANAT(1) and AANAT(2)) and two subtypes of melatonin receptor (Mel-R; Mel(1a) and Mel(1b)) in several fish species has led to rapid advances in characterizing the physiological roles of melatonin. In the present study, partial cDNAs encoding these four genes were cloned from the eye and brain of chum salmon (Oncorhynchus keta). Based on the nucleotide sequences, we developed highly sensitive real-time PCR systems for these four mRNAs. The development of daily rhythmicity in AANAT(1), AANAT(2), Mel(1a), and Mel(1b) transcript levels was examined in the eye and brain of chum salmon during embryonic and post-embryonic stages (from day -9 to day +180). In a parallel experiment, ocular and brain melatonin levels were measured by radioimmunoassay. Parallelism in developmental changes and in circadian rhythms of AANAT mRNAs and melatonin levels in the eye and the brain supports a hypothesis that the developmental increases of nocturnal melatonin levels results partly from the elevated transcription of AANAT genes. Moreover, abundant expression of AANAT and Mel-R mRNAs in the optic tectum, thalamus, hypothalamus, cerebellum, and eye indicates possible roles of melatonin in visual processing and neuroendocrine regulation, through which melatonin might be involved in migratory behavior of chum salmon.

Cryopreservation of chum salmon blastomeres by the straw method.

In order to preserve genetic resources of chum salmon, Oncorhynchus keta, optimum conditions for cryopreservation of isolated blastomeres were investigated. Survival rates under various conditions were compared: the nature and the concentration of cryoprotectants before and after freezing, the seeding temperature, and the developmental stages of donor embryos. Isolated blastomeres immersed for 30 min in Eagle's MEM containing both a cryoprotectant and 10% fetal bovine serum (FBS) at 10 degrees C were transferred into a straw and frozen at 1 degrees C/min to -30 degrees C by a programmable freezer before being plunged into liquid nitrogen. Ice seeding was carried out at -5 to -15 degrees C. Frozen blastomeres were thawed in water at 15 degrees C. Blastomeres cryopreserved with MEM containing 10% dimethyl sulfoxide (Me(2)SO) and 10% FBS (10% Me(2)SO/MEM10) showed higher survival rates than those cryopreserved with MEM containing 10% FBS and 10% glycerol, ethyleneglycol, 1, 2-propanediol, or sucrose. Blastomeres treated with 10% Me(2)SO/MEM10 showed higher survival rates than those treated with MEM containing only 10% Me(2)SO. Blastomeres seeded above -10 degrees C showed higher survival rates than non-seeded ones. Frozen blastomeres at advanced stages demonstrated high survival rates. Blastomeres cryopreserved under optimum conditions showed survival rates of 59.3+/-2.8%. These results indicate that 10% Me(2)SO/MEM10 is a suitable cryoprotectant medium to cryopreserve chum salmon blastomeres, that seeding should be carried out above -10 degrees C on pre-freezing, and that blastomeres at the blastula stage should be used as material.

Intracerebral expression of gonadotropin-releasing hormone and growth hormone-releasing hormone is delayed until smoltification in the salmon.

A developmental strategy was employed to investigate the functional assembly of neuropeptidergic systems in the migratory species of chum salmon Oncorhynchus keta. Using immunocytochemistry we have demonstrated that different groups of gonadotropin-releasing hormone- (GnRH)- and growth hormone-releasing hormone- (GHRH)-synthesizing neurons emerged according to very different developmental timetables. From the eye pigmentation stage (23 +/- 2 days after fertilisation (DAF)) through to the pre-smoltification stage (136 DAF), salmon-GnRH neurons originating from the olfactory placodes remained restricted to the extracerebral course of the terminal nerve. At the climax of smoltification (downstream migration 167 DAF), basal forebrain and midbrain GnRH neurons with elaborate neurite outgrowths in the brain and the pituitary became detectable. The GnRH neuroanatomical organization in the post-smoltification stage (197 DAF) was similar to that in the smoltification stage (167 DAF). In contrast to the case for other teleosts, chicken-GnRHII neurons were not found in the midbrain but were localized along the medial regions of the olfactory nerve. Growth hormone-releasing hormone immunoreactivity in the olfactory apparatus (21 DAF), and fibers along the basal telencephalon and hypothalamus and in the pituitary were observed during early embryogenesis (51 DAF) and in cells in the preoptic area on 167 DAF. The intracerebral expression of GnRH and GHRH was not detected until the peak of smoltification, which coincided with a peak in thyroid hormones, and precisely with downstream migratory behavior.