Reijiro Hirano

Cryopreservation of carp sperm

Abstract About 70% of eggs of Cyprinus carpio reached the eyed stage in fertility tests with 1 ml of cryopreserved semen added to 1 g of eggs. When 1 ml of semen was added to 100 g of eggs, few eggs reached the eyed stage. In two fertility tests with sperm preserved for 342 days, using 5 g of eggs inseminated with 1 ml of semen, percentages of eyed eggs were 31.5 and 25.5, respectively. In a series of fertility tests, the chemical constituency of the medium in which fertilization was attempted influenced the fertility of cryopreserved sperm.

Growth and reproduction of the epifaunal amphipod Caprella okadai Arimoto (Crustacea : Amphipoda : Caprellidea)

Abstract Growth, maturation and reproduction of Caprella okadai Arimoto, an amphipod crustacean endemic to the Japanese coast, were studied under laboratory conditions at 20°C, and 14 h light: 10 h dark photoperiod. The diatom Cylindrotheca closterium (Ehrenberg), and the red alga Gelidium amansii (Lamouroux) were provided for food and clinging substratum. Juveniles newly emerged from the brood pouch molted at 2.9–6.8-day intervals. Body lebgth increased per instar of both males and females represented a sigmoid curve. On average, females reached sexual maturity at instar VII at 20.1 days of age, produced their first brood at 20.6 days, and had 3.8 successive cutches at 5.0–6.0-day intervals. The number of embryos per brood increased from 10.8 at instar IX. A female produced an average of 36.1 offspring throughout her life span. The similarity of life history patterns of C. okadai and C. Danilevskii Czerniavski indicates that habitat segregation of these two species results from morphologicaal adaptations of caprellids to their respective localities.

Duration and size of embryos in epifaunal amphipods Caprella danilevskii Czerniavski and C. okadai Arimoto (Crustacea:Amphipoda:Caprellidea)

Abstract Embryonic duration in two species of epifaunal caprellid amphipods, Caprella danilevskii Czerniavski and Caprella okadai Arimoto, was investigated. The duration decreased from 13 days at 10°C to 3.5 days at 24°C in C. danilevskii and 8.2 days at 12°C to 3.4 days at 24°C in C. okadai . The embryonic duration can be expressed using Belehradeks equation which indicates “biological zero”, α, at 5.5°C in C. danilevskii and 6°C in C. okadai . The generation period of both species was estimated based on Belehradeks equation of embryonic development and the generation period at 20°C obtained in our previous studies; 53.2 days at 12°C to 20.8 days at 24°C in C. danilevskii , 54.9 days at 12°C to 20.4 days at 24°C in C. okadai . Embryo size was also noted during field collections; C. danilevskii embryos increased from 0.40 × 0.33 mm in the early stage to 0.46 × 0.37 mm in the late stage and C. okadai from 0.34 × 0.28 mm to 0.37 × 0.30 mm.

Effects of glutaraldehyde fixation on the body size of red sea bream (Pagrus major) larvae

Abstract The use a buffered 2.5% glutaraldehyde solution as a fixative for red sea bream larvae was investigated. Morphometric data were obtained from live larvae 3, 12, 18, and 25 days old. These were then fixed for a period of 6 months and were remeasured. The only significant changes between live and preserved specimens were in body and muscle depth in 3-day-old specimens. Compared to conventional formalin-fixed specimens, the glutaraldehyde-fixed specimens had negligible shrinkage and a more natural appearance.

Optical, biological, and chemical properties ofAoshio, hypoxic milky blue-green water, observed at the head of Tokyo Bay

Aoshio-hypoxic water which can be distinguished from surrounding coastal water by its milky blue-green color-is often observed at the head of Tokyo Bay when coastal upwelling of sulfidic bottom water occurs during summer and early autumn. Optical properties and the biological-chemical composition of suspended matter in theaoshio water were investigated using nearby “normal” coastal water as a reference.Suspended matter in theaoshio water contributed to the large beam-attenuation coefficient and also to the strong upward radiance with maximal intensity around 550 nm as a result of the scattering process. No significant difference in bacterial density was observed between samples ofaoshio water and reference coastal water. The low chlorophylls concentration inaoshio water samples indicates that biological pigments may not play a dominant role in the color of theaoshio events.The suspended particles inaoshio water samples had much higher contents of sulfur and manganese and a lower silicon content than those in reference coastal water samples. The colloidal elemental sulfur and manganese-rich particles identified in theaoshio water appear to be oxidation products of dissolved sulfide and manganese (II) in the anoxic water.On the basis of these findings, it may be concluded that there is a high probability that elemental sulfur and manganese-rich particles are responsible for the color and turbidity inaoshio.

Effects of bacterial films on diatom attachment in the initial phase of marine fouling

The effects of bacterial films on diatom attachment were examined in short-term laboratory experiments, comparing the density of immotile pennate diatoms attached to plates previously coated with bacterial films (BP) with that of sterile plates (SP). The predominant diatom and bacterium wereSynedra sp. andAlcaligenes sp., respectively. There was no significant difference between densities of diatoms on SP and those on BP at each contact time (2, 5, 10, 30, 60 min), although bacterial densities on BP were 17 to 185 times those on SP. Moreover, SEM observations showed that the percentage of diatoms in contact with bacteria on SP were quite low. The results of this study indicate that a bacterial film is not always necessary for diatoms to attach to substrata and that the film ofAlcaligenes sp. had no effect on the attachment ofSynedra sp.

Effects of Water Temperature and Photoperiod on the Spawning Cycle of the Sand Borer, Sillago sihama

Abstract Sand borer, Sillago sihama (Forskal), spawns every day or every other day during its extended spawning season. Unnecessary spawning could cause problems in fish growth, egg quality and water quality. Environmental factors were manipulated in this study to investigate the signals which initiate and conclude the spawning season, as well as adjust the daily spawning rhythm of the sand borer. The results show that temperature might be the most significant environmental factor for them initiation and termination of the spawning season. Photoperiod would affect the daily spawning rhythm.

Organisms Suitable as Food for Larvae of Black Sea Bream

Abstract Different organisms were tested as food for larvae of the black sea bream (Mylio macrocephalus): rotifers (Brachionus plicatilus) cultured on Chlorella; rotifers cultured on baking yeast (Saccharomyces cerevisiae); nauplii of the brine shrimp (Artemia salina); and the copepod Tigriopus japonicus. Black sea bream larvae were 20 days old at the beginning of the 18-day test period; surviving test groups were held for an additional 12-day feeding period. The suitability of brine shrimp nauplii to the larvae appeared to be limited; mortality began after the larvae had been fed Anemia nauplii for 7 days. No mass mortality was observed in either of the rotifer-fed groups; however, larvae fed yeast-cultured rotifers grew more slowly and appeared to be weaker than those fed on Chlorella-cultured rotifers. Chlorella-cultured rotifers were the most suitable of the test foods for larvae less than 10.7 mm in fork length, whereas Tigriopus was the most suitable for larvae larger than 10.7 mm. Larvae fed on Tig...