An improved method for studying the condition of fish, with an example using Pacific sardine Sardinops sagax (Jenyns)

The statistical treatment of condition used in many previous studies has been to determine a predicted weight for a fish, and to calculate a ratio of actual to predicted weight. The ratios obtained, known as condition factor K , are then further analysed using analysis of variance or other techniques to relate changes in K to other independent variables. It is suggested that condition can be studied better by using a single model to analyse the response of fish weight to a number of factors simultaneously. This approach affords benefit from the simplicity of using an integrated analysis and avoids problems with skewed distributions of ratios. An example using data on the Pacific sardine, Sardinops sagax (Jenyns), is given. Changes in condition of this fish due to monthly, yearly and temperature effects are calculated.     

Changes in ovarian development and plasma levels of sex steroid hormones in the wild female Japanese sardine (Sardinops melanostictus) during the spawning period

In order to clarify the spawning pattern of Japaneses sardine ( Sardinops melanostictus ) during the spawning period, changes in ovarian histology, frequency distributions of oocyte diameter and plasma levels of oestradiol-17β (E₂) and 17 a ,20β-dihydroxy-4-pregnen-3-one (17 a ,20β-diOH-P) were examined in female fish captured in the region off Kyushu and Shikoku in Japan. With the development of the ovary, the gonadosomatic index (GSI) increased gradually and the size of oocytes became larger. When the GSI exceeded 13, the translucent hydrated eggs began to dominate and ovulation subsequently occurred. After ovulation, GSI decreased to less than 3. Post-ovulatory follicles were found only in the lower GSI ranges and atretic oocytes were always observed in the ovary. Plasma E₂ levels increased along with ovarian development but decreased after completion of yolk accumulation. On the other hand, 17 a ,20β-diOH-P showed the highest level just before and after ovulation. Ovarian histology and hormonal profiles suggest that the sardine spawns repeatedly during the spawning period. Based on the concentration of 17a,20β-diOH-P, the female Japanese sardine was estimated to ovulate before the middle of the night.     

Interannual fluctuations in recruitment and growth of the sardine,Sardinops melanostictus,in the sea of Japan and adjacent waters

Recruitment and growth of the sardineSardinops melanostictus fluctuated markedly in the Sea of Japan and adjacent waters between 1978 and 1993. Stock size was calculated using Virtual Population Analysis and average body length in each age class was determined by the number of annual rings on the scales. There is an inverse correlation between average water temperature at a depth of 50 m in the coastal area of the mainland of Japan in winter (January to March) and recruitmentR defined as the number of individuals at 1 year old. There is also an inverse correlation between spawning stock sizeE and reproductive success in (R/E). A multiple regression model using spawning stock size and water temperature in winter as independent variables can explain 73% of variance in reproductive success. It suggests that both density-dependent and density-independent factors perform important roles determining reproductive success. There is an inverse correlation between body length and stock size and this suggests that there is a density-dependent effect on the growth of the sardine.     

Osteological development of the feeding apparatus in early stage larvae of the seabass,Lates calcarifer

The osteological development of the feeding apparatus was examined in early stage larvae of laboratory-reared seabass,Lates calcarifer. At initial mouth openings 40 hours after hatching, the larvae were equipped with the fundamental elements forming the oral cavity, such as the trabecular roof, the lower branchial and hyoid arches forming the floor, the quadrate and symplectic-hyomandibular cartilages making up the sides, and the maxilla and Meckel's cartilage bordering the jaws. The cleithrum appeared almost simultaneously. The mechanics of creating a negative pressure in the oral cavity, which results in a “sucking” mode of feeding, were elucidated from these elements. During a period from 50–60 to 100–110 hours after initial mouth opening (HAMO), new elements such as the premaxilla and jaw teeth appeared, and the ossification of existing elements started. The new elements apparently enabled the larvae to “grasp” food organisms, in addition to the already existing and increasing sucking ability, from 100–110 HAMO.     

The ontogeny of kin recognition in tadpoles of the toadBufo melanostictus (Anura; Bufonidae)

The ontogeny of kin recognition and influence of social environment on the development of kin recognition behaviour was experimentally investigated in tadpoles of Bufo melanostictus that lived in aggregations and showed low larval dispersion. Embryos and tadpoles of the toad were reared as (i) kin only, (ii) with kin and non-kin (separated by a mesh screen), and (iii) in isolation. They were tested for the ability to discriminate between (i) familiar siblings and unfamiliar non-siblings, (ii) familiar siblings and familiar non-siblings and, (iii) unfamiliar siblings and unfamiliar non-siblings. All tadpoles were fed on boiled spinach before conducting trials. Preference of test tadpoles to associate near the end compartments whether empty or containing members of specific stimulus groups was assessed using a rectangular choice tank. When tested in tanks with empty end compartments, the test tadpoles showed random distribution and thus no bias for the apparatus or the procedure. In the presence of kin/non-kin in the end compartments a significantly greater number of test tadpoles spent the majority of the time near familiar or unfamiliar kin rather than near familiar or unfamiliar non-kin. Kin discrimination ability persisted throughout larval development. Familiarity with siblings is not required for discriminating kin from non-kin, and kin discrimination ability is not modified following exposure to non-kin. Also, involvement of dietary cues is unlikely to be the prime mechanism of kin recognition inB. melanostictus unlike in some other anurans.     

Histological effects of vitamin A on the tail amputated tadpoles ofBufo melanostictus

Vitamin A has manifold effects on the development, growth and pattern formation of several amphibians. At the same time it causes severe embryonic malformations. The histological changes brought about by vitamin A in the tail tissues of anurans are quite amazing. A common morphological change brought about by vitamin A in tail-amputated tadpoles ofBufo melanostictus include the formation of a large bulbular mass at the distal end of the tail following tail regeneration. Histology revealed that the bulbular mass consisted of notochordal cells only. Other histological changes are: a thickening of the epidermis and the basement membrane, enlargement of the notochord and the nerve cord, thickening of the sheath covering the notochord and the myelin sheath covering the nerve cord and the disorganization of muscle bundles. The significance of such changes is discussed.     

Osteological development of the lumpfish,inimicus japonicus (pisces: Synanceiidae)

The osteological development of the synanceiidInimicus japonicus, was described on the basis of five larvae and four juveniles (4.2–10.1 mm BL) reared in the laboratory, and two wild adult specimens. All bones, except for the basisphenoid, were formed in all larvae and juveniles, but fusions between the uppermost actinost and scapula, upper caudal plate and urostyle, and third preural centrum and hemal spine were not completed by 10.1 mm BL. Following comparison with the adult condition, a rod-like ossified bone without a tooth plate on the upper branchial arch of larvae and juveniles was considered homologous with the second pharyngobranchial. The number of epurals and length of the neural spine on the second preural centrum varied (unrelated to growth) and it is inferred thatJ. japonicus shows intraspecific variations in these bones.     

Thermal behavior of the Pacific sardine (Sardinops sagax) acclimated to different thermal cycles

The study of thermal behavior of fishes provides useful data to enable predictions of the effect of climatic change on populations so as to ensure good management of fisheries. The Pacific sardine has a complex population dynamics; three subpopulation have been proposed (cold, temperate and warm).We exposed Sardinops sagax caeruleus (temperate sub-population) to two different thermal cycles, which were chosen to be consistent with the temperatures reported in two distant places Cedros Island (CIc: 18–23 °C) and San Pedro (SPc: 13–18 °C).The thermal behavior of the SPc and CIc sardines was affected by acclimation treatment: the interval of thermal preference was 17.1–19.9 and 16.0–18.8 °C, while the lethal temperatures interval (LT50) was 7.7–25.6 and 6.9–24.3 °C, and the critical limits CTMax and CTMin were 7.1–32.2 and 5.5–30.4 °C, respectively.The results of thermal behavior showed that sardines of the temperate subpopulation are more tolerant to cold; this might suggest that they would be more able to survive in California and Oregon than in Baja California Sur and the Gulf of California.     

Temperature and humidity alter prolactin receptor expression in the skin of toad (Bufo bankorensis and Bufo melanostictus)

Bufo bankorensis and Bufo melanostictus, the only two species of Bufonidae genus in Taiwan, live in habitats that differ in altitude and humidity. This study tested the hypothesis that prolactin receptor (PRLR) expression responds to environmental change. Western blot analysis showed that the PRLR protein was widely distributed in brain, lung, liver, kidney, dorsal skin and ventral skin of toads. The level PRLR protein was elevated in the dorsal skin of the two toad species treated with dry or wet conditions for 14 days. The increase in PRLR of dorsal skin in B. bankorensis was higher than that in B. melanostictus. This experimental result suggests that B. bankorensis secretes more mucus to reduce water evaporation from its thinner cuticle than B. melanostictus. The expression of PRLR protein was increased in the lung of B. bankorensis and decreased in the lung of B. melanostictus. Moreover, PRLR protein levels were increased in the kidneys in the two species toad, likely due to reduction in water lost through lung and urine. The two toad species were subjected to varying temperatures (25 degrees C, 15 degrees C and 10 degrees C) for 14 days. The lowest PRLR protein expression was observed at 10 degrees C. Comparison of the decreasing trend in PRLR protein levels demonstrated that the variation in B. bankorensis was significantly higher than that in B. melanostictus. Comparisons of variation in PRLR protein expression in the two species under different environments suggest that B. bankorensis is more adaptable to different environments than B. melanostictus.     

Large schools of Japanese sardines,Sardinops melanostictus, mate in single pair units at night

Synopsis We observed the behavior of the spawning group of Japanese sardine,Sardinops melanostictus, in the field at night, and also confirmed the spawning behavior in the darkness in captivity. The chasing and mating were done in a pair of 1 male and 1 female. The 1-to-1 mating was a definite finding irrespective of the group density in the field, the density in the tank in captivity, or the sex ratio. This maybe because there is little visual information during spawning at night.     

Occurrence of an alternative pathway in the larval development of the crab Chasmagnathus granulata Dana, 1851 under laboratory conditions

Larvae of the crab Chasmagnathus granulata were collected in a salt marsh located in the Lagoa dos Patos, Brazil and reared from eclosion to metamorphosis under different dietary regimes. Larvae reared individually in beakers of 40 ml and fed Tetraselmis chuii (zoea III and zoea IV), showed a supplementary stage, here designated as zoea V, with morphological characteristics intermediary between zoea IV and megalopa. No zoeae V molted to megalopa stage. To confirm the occurrence of the supplementary stage, mass cultures of larvae of C. granulata were fed Artemia sp. at high densities, we again detected the fifth zoeal instar. However, when zoeae V were individually placed in beakers and fed Artemia nauplii, they succeeded in molting into megalopae. We observed the occurrence of two types of zoeae IV — a smaller type (from which originated the zoeae V) and a larger type (which directly developed into megalopae). We conclude that stressful nutritional/environmental conditions were responsible for the occurrence of this alternative path of development.     

Amylostereum laevigatum associated with the Japanese horntail,Urocerus japonicus

The fungus associated with the Japanese horntail,Urocerus japonicus, in Kochi, Kagawa and Ehime Prefectures was studied. Cultures isolated from the mycangia of 113 adult females of the horntail showed the same cultural characteristics. Four of basidiocarps found on felled logs ofCryptomeria japonica were identifieds asAmylostereum laevigatum based on morphological characteristics. This was the first record ofA. laevigatum from Japan. The cultures isolated from the basidiocarps had the same cultural characteristics as those from the mycangia ofU. japonicus. One mycangial isolate produced basidiocarps on artificially inoculated stem segments ofCr. japonica after a 6-mo incubation and was identified asA. laevigatum. One isolate from the basidiocarps ofA. laevigatum and one from the mycangium ofU. japonicus were artificially inoculated into five trees each ofChamaecyparis obtusa andCr. japonica. The wood of all inoculated trees showed discoloration, with no difference in shape and pattern of discoloration between the two isolates. The inoculated fungi were reisolated from the areas of discoloration in the inoculated trees.     

Addition and reexamination of Japanese species belonging to the genusCercospora and allied general II Species described by Japanese mycologists (1)

In this second report of the present series, six species ofCercospora described in Japan were transferred to the genusPseudocercospora after detailed reexamination. They arePseudocercospora abeliae, P. chionanthi-retusi, P. corylopsidis, P. ehretiae, P. naitoi andP. paulowniae.     

Larval development ofMacrophthalmus erato De Man, 1887 (Brachyura ocypodidae)

The zoeal and megalopal stage ofMacrophthalmus erato were obtained under laboratory conditions and are described and figured. Five zoeal and one megalopal stages were reared at 25; salinity and temperature of 29°C. Their features are compared with those of known species of the genus.     

A comparative study of the ontogenetic development of the cupules inCastanea andLithocarpus (Fagaceae)

Two contradicting theories have been proposed for the morphological nature of fagaceous cupules; the intercalary growth theory and the higher order dichasial branch theory. All the previous ontogenetic studies insist on the latter one, but the genera investigated have been rather restricted and have not covered all the cupule types. A comparative study of the ontogenetic development of cupules inCastanea crenata andLithocarpus edulis, which are representatives of fundamentally different cupule types, revealed that both the theories are incomplete. InL. edulis, the higher order dichasial branches contribute to cupule formation along the anterior portions of the lateral flowers. However, along the adaxial portion of the central flower, the cupule develops as an intercalary growth, represented by rapid increase of tangentially oblong epidermal cells. InCastanea, intercalary growth is not clearly observable, for presumably, the flowers are surrounded by a well-developed partial inflorescence mound from the beginning of development.Contributions from the Osaka Museum of Natural History No. 305.     

Rover/sitterDrosophila melanogaster larval foraging polymorphism as a function of larval development,food-patch quality,and starvation

The genetically based rover/sitter behavioral difference in Drosophila melanogasterlarval foraging is expressed throughout most of the larval instars when larvae forage on food patches of differing food quality. The amount of locomotor behavior decreases when third-instar larvae of both rover and sitter strains are starved just prior to the behavioral test. Such strain differences in locomotor behavior are maintained despite the starvation-induced decrease in locomotion found in both strains. Measurements of larval body length and width, taken at 24, 48, 72, and 96 h posthatching, reveal that rover and sitter larval growth rates do not differ. The finding that rover/sitter differences are expressed in a variety of environments and throughout the majority of the larval instars should aid in attempts to uncover selection pressures which may differentially affect the two morphs in environmentally heterogeneous natural populations.     

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia)

Larval development of the rhizocephalanSacculina polygenea (Crustacea: Cirripedia: Rhizocephala) parasitizing the coastal crabHemigrapsus sanguineus was studied in Vostok Bay, the Sea of Japan. At 22–23°C, the entire cycle of larval development takes 2.5 days and includes five naupliar stages and one cypris stage. Like other rhizocephalans, the larvae ofS. polygenea are lecithotrophic and only grow slightly in size in the course of development, and like all sacculinids, they have no flotation collar. The naupliar stages IV and V have a tubercle between the furcal rami; this tubercle is absent in the larvae of the genusPeltogasterella, but it has been described inS. carcini. The first seta of the antennule only disappears completely at the fourth stage, although it is markedly reduced at the third stage. No morphological differences, except differences in size, are found between male and female nauplii.     

Parenchymal fine structure of the subfornical organ in the Japanese quail,Coturnix coturnix japonica

Summary The parenchyma of the subfornical organ (SFO) of the Japanese quail was studied by light and electron microscopy. The SFO consists of ependymal, intermediate, and basal (perimeningeal) layers. In the intermediate layer, neurons, glial cells, and their processes are found. Axons containing dense core granules approximately 80 nm in diameter are numerous, some of which make synaptic contact with the neuronal perikarya or dendrites. Synaptic vesicles in some axons contain a dense dot in the interior after treatment with 5-hydroxydopamine. The activity of the SFO, which is probably concerned with elicitation of drinking by angiotensin II, may be regulated at least partly by afferent monoaminergic axons. Capillaries with a non-fenestrated endothelium are occasionally found in the parenchyma. The basal layer is occupied by glial processes abutting on the digitating layer of perivascular connective tissue of meningeal vessels. The endothelium of these vessels is occasionally fenestrated. Trypan blue injected systemically accumulated in the SFO, but not in the deeper areas of the brain. The absence of a blood-brain barrier is suggested in the SFO.