Structural Characteristics,Properties, and In Vitro Digestibility of Rice

Using rice samples derived from normal rice cultivars and endosperm starch mutant, we investigated key factors contributing to the enzyme digestibility of steamed rice grains. The chemical composition of polished rice grains, structural features of endosperm starch, and enzyme digestibility of steamed rice grains were examined. The protein content of polished rice grains was 4.6–9.1%, amylose content was 4–27%, the DP_n of purified amylose was 900–1,600, the amylopectin short/long chain ratio was 1.2–5.9, and the enzyme digestibilities of steamed polished rice grains were 0.9–12.6 °Brix. Amylose content and RVA parameters (viscosity, breakdown, and setback) correlated significantly with enzyme digestibility of steamed rice grains. Multiple regression formulas were constructed to predict digestibility of steamed rice grain as a function of the molecular characteristics of the starch. When both amylose content and the short/long chain amylopectin ratio were used as predictor variables, they accounted for >80% of the observed variance in digestibility of steamed rice grains. Multiple regression revealed that the more digestible rice samples had starch with a lower amylose content and more short‐chain amylopectin. Reassociation of amylose‐lipid complex and recrystallization of amylopectin in the stored steamed rice grains was monitored by differential scanning calorimetry (DSC), and the observed retrogradation properties were related to the structural characteristics of starch and to the enzyme digestibility of steamed rice grains.     

Influence of temperature and feeding regimes on growth and notochord deformity in reared <Emphasis Type="Italic">Anguilla japonica</Emphasis> leptocephali

The high mortality rate of reared Japanese eel Anguilla japonica larvae is largely due to lower growth rate and the higher rate of deformed larvae. To establish an effective rearing protocol for this species, we examined the effects of water temperature and feeding regimes on their growth and notochord kyphosis. Larvae at 165 days post hatching were reared for 28 days at mean temperatures of 24, 25 and 27 °C, and were fed 4 or 6 times per day. Larval growth rate was significantly higher in larvae reared at 24–25 °C and fed 6 times per day. However, growth rate was significantly reduced at 27 °C, suggesting a shortage of metabolic energy due to an elevated cost of the higher basal metabolic rate at higher temperatures and low nutritional performance of currently used artificial diet. Notochord kyphosis was promoted by elevated water temperature, and two-way ANOVA showed that water temperature and feeding frequency had combined effects on the deformity. These findings suggest the importance of concurrently manipulating both environmental and nutritional factors to produce healthy eel larvae in captivity.     

Population structure of the Japanese eel Anguilla japonica as examined by mitochondrial DNA sequencing

SUMMARY: To examine the population structure of the Japanese eel Anguilla japonica , mitochondrial DNA sequence analysis was made for various samples of glass eels that might reflect genetic characteristics of spawning aggregates. The mitochondrial DNA from a total of 51 glass eels collected at Tanegashima Island, Kanagawa and Ibaraki in different periods within an inshore migrating season was sequenced for a 615 base-pair fragment from the tRNA^Thr gene to the central part of the control region. The DNA region was so variable that no individual was found to possess the same sequence, although average sequence differences within samples (1.07–1.63) were not large. Average sequence differences between samples (1.22–1.57) were comparable to those within samples, suggesting no genetic heterogeneity among samples. Tree analysis of the sequences showed neither a geographical nor temporal structure of population. Furthermore, although all DNA sequences from the present study were different from one another, two sequences were found to be the same with those reported from individuals collected in different localities in different years. Altogether, the present mitochondrial DNA sequence analysis of glass eels did not provide any evidence for genetic subdivision of the Japanese eel population.     

First capture of post-spawning female of the Japanese eel Anguilla japonica at the southern West Mariana Ridge

Two adult male freshwater eels, Anguilla japonica, were captured in June 2008 in the West Mariana Ridge (13°N, 142°E) in the North Pacific, but collections of females have yet to be reported. In September 2008, we successfully caught two adult female A. japonica, 55.5 and 66.2 cm in total length, in the adjacent but northern area (14°N, 143°E). Six newly hatched eel larvae (pre-leptocephali) were also collected by subsequent plankton sampling conducted near the female catch area. Female adults appeared to be in the post-spawning state, probably a considerable time after spawning, since a small number of remarkably regressed oocytes (50–250 μm in diameter) were observed in the ovaries. Capture of post-spawning female eels and newly hatched larvae near the Suruga Seamount (14°N) together with the previous collection of mature males in the southern area (13°N) corroborates that the area along the West Mariana Ridge is the spawning area of this species, but suggests that the eel spawning may occur over a wider area than previously expected.     

Involvement of sex steroids,luteinizing hormone and thyroid hormones in upstream and downstream swimming behavior of land-locked sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis>

The involvement of testosterone (T), estradiol-17β (E₂), 11-ketotestosterone (11-KT), 17,20β-dihydroxy-4-pregnene-3-one (DHP), luteinizing hormone (LH), thyroxine (T₄), and triiodothyronine (T₃) in the regulation of downstream and upstream movement (swimming behavior) was investigated in land-locked sockeye salmon Oncorhynchus nerka, using an artificial raceway. During the downstream migratory period, T implant resulted in high plasma T levels and inhibited the occurrence of downstream swimming behavior (negative rheotaxis) in yearling (1+) immature smolts. In terms of upstream behavior, 2-year-old (2+) males exhibited high plasma T and 11-KT levels, while 2+ females had elevated T and DHP levels. In 1+ immature fish, a T implant induced upstream swimming behavior (positive rheotaxis). In experiments 1 and 3, the plasma T₄ and T₃ levels of non-migrants tended to be higher than those of migrants. In contrast, no marked changes in plasma and pituitary LH were found in both downstream and upstream migrants. These results suggest that sex steroids, such as T, play significant roles in the regulation of downstream and upstream swimming behaviors in land-locked sockeye salmon.     

A new liquid-type diet for leptocephali in mass production of artificial glass eels

Fisheries Science - Development of artificial production of glass eels still presents many problems to be solved. What and how to feed larvae is one of the most crucial problems for commercial mass...     

Genetic identification and morphology of naturally spawned eggs of the Japanese eel Anguilla japonica collected in the western North Pacific

Eggs of the Japanese eel Anguilla japonica collected in the western North Pacific were identified by onboard species-specific polymerase chain reaction (PCR) and DNA nucleotide sequencing after the cruise. Fish eggs of various species were collected by large plankton net tows at 12 stations along the southern part of the West Mariana Ridge on 19–25 May 2009. A total of 43 fish eggs were distinguished morphologically as possibly being of A. japonica. Thirty-one of those were analyzed by PCR, which included 15 eggs collected at 12°50–55′N, 141°15–20′E (in 5 tows) that showed positive results. The 16S ribosomal RNA (rRNA) gene sequences of eggs determined after the cruise indicated that 31 A. japonica eggs had been collected. The remaining eggs were of mesopelagic eel species (Serrivomeridae and Derichthyidae), or unidentified species. The morphological characteristics of the A. japonica eggs were consistent with those of artificially spawned eggs, except they had a slightly larger diameter. The egg diameter range did not overlap with those of mesopelagic eels of the Serrivomeridae, which often spawn in the same area as A. japonica. These results suggest that egg diameter and embryo shape can be used to morphologically identify naturally spawned A. japonica eggs.