埃及尼罗河鲶的精子发生和精子的超微结构

用扫描和透射电子显微镜研究了尼罗河鲶——盾头歧须鮠(Synodontis schall)的精子发生和精子的超微结构。精巢中含有无数肾形的生精小叶,我们将其称为"精原无限型"。尽管其精子发生的大体过程与同类鱼无异。但是,在细节上仍具其独特之处。这些特点未见在其他硬骨鱼中报道过。其特点主要是:生精过程中不发生细胞核的旋转,中心粒复合体和轴丝起始段直接发生在核的基底面垂直线上,有无数的粗的固定纤维将近端中心粒和远端中心粒的近侧部连接到细胞核上。另外,精子发生过程中还包括染色质浓缩,细胞质和线粒体向细胞核的尾端迁移,在核的后端中轴位置上形成中等大小的核后凹,近端中心粒和远端中心粒的一部分嵌在核后凹之内,短的胞质内陷管将线粒体与鞭毛分隔开。精子头部接近圆形,无顶体或顶体泡,鞭毛的中段及胞质内陷管均较短,整个鞭毛却很长,鞭毛侧面无翼膜,轴丝呈典型的9 2结构。上述结果显示,盾头歧须鮠的精子发生具有类型Ⅰ和类型Ⅱ的共同派生特征,这种特征在常见的其他硬骨鱼中也是常有的。但是,正如文献所报道过的另两种尼罗河鲶——金鯵(Chrysichthys auratus)和电鲶(Malapterurus electricus)中的情况一样,盾头歧须的精子发生与类型Ⅲ的精子发生过程更为相似。     

Pectoral spine size in Synodontis schall (Teleostei: Mochokidae) from Asa Lake, Ilorin, Nigeria

The pectoral spines of Synodontis schall (n = 813) were examined for 24 months. Mean length for the right (3.2 cm) and left (3.1 cm) pectoral spines were not significantly different [P > 0.05]. However, the male and female pectoral spine lengths were significantly different (P < 0.05). A fractured pectoral spine in one of the specimens was shorter than the other. The fracture which could be deleterious to balancing, feeding and reproductive activities was attributed to an injury rather than to genetic or epigenetic defects.     

The food and growth of pelagic 0+ Alestes nurse (Characidae) from the Blue Nile,near Khartoum

The food, feeding habits and growth of 0+ Alestes nurse (Rüppel) from the Blue Nile near Khartoum, was investigated. 0+ A. nurse were observed to change their food from phytoplankton and small zooplankton during their pre-metamorphosis stages, to larger zooplankton (Daphnia spp., Chydorus sp.) and insects (larvae, pupae and imagines) during their post-metamorphosis stage.Their growth in length and weight was characterized by two distinct stanzas; during the first stanza, the fish increased in total length at a rate of 0.196 mm mm^–1 wk^–1, and in wet weight at a rate of 0.430 g g^–1 wk^–1. These rates were reduced during the second stanza to 0.046 mm mm^–1 and 0.080 g g^–1 wk^–1, respectively. The calculated value of the exponent b in their length-weight relationship suggested that their growth was allometric.     

Physical and chemical characteristics of the Blue Nile and the White Nile at Khartoum

Fortnightly measurements of physical and chemical variables were made at two locations on the Blue and White Niles near Khartoum from August 1968 to December 1970. Variables analysed from each river were: temperature, pH, total residue, current velocity, oxygen, alkalinity, phosphate, nitrate, ammonia, silica, sulphate, iron, calcium, magnesium, sodium, potassium and oxidizable organic matter. The seasonal variations of these factors in the two Niles are compared and the interrelationships existing between some of them are discussed. Comparisons with earlier studies on the Nile and with some tropical rivers are made.In the Blue Nile, the amounts of suspended matter and nutrients are largely dependent upon the flood regime. Nitrate, phosphate, iron, oxidizable organic matter and total residue increase considerably in the Blue Nile when the river is in flood (peaks: 1 880 µg NO₃-N l^–1; 0.31 mg Fe l^–1; 3 842 mg total residue · l^–1).In the White Nile, concentrations of nitrate, phosphate, iron, oxidizable organic matter and total residue attain their peaks during the rainy season (270 µg NO₃-N l^–1; 163 tag PO₄-P l^–1; 0.46 mg Fe · l^–1; 502 mg total residue · l^–1).In both rivers, alkalinity, calcium, sodium and potassium tend to increase during the dry season while declining in the rainy season. Silica is depleted at certain times of the year, yet relatively high concentrations are maintained throughout the year and were not expected to limit growth of diatoms. Fall in silica concentrations, unlike nitrate, phosphate and iron, was always followed by a rapid restoration of a high level. Silica and magnesium showed no response to changes in discharge rates.     

Some aspects of the reproductive biology of Acanthopagrus spp. (Family: Sparidae)

Changes in the seasonal development of the gonads in Acanthopagrus latus and A. cuvieri over an annual reproductive cycle are described. There is one major spawning period from January to March. Hermaphrodite A. latus and A. cuvieri constituted 5.8% and 5.7% of the total sample respectively. The histological changes in the ovary, testis and ovo-testis in both species are described. Fecundity estimates for A. latus , 27.5–31.8 cm, ranged from 1 362 137 to 2 152 993, and estimates for A. cuvieri , 47.1–63.5 cm, ranged from 308 273 to 1 693 365.     

Some aspects of the reproductive biology of the clupeid Ilisha africana (Bloch) off the Lagos Coast, Nigeria

The maturation development, spawning period, oogenesis, fecundity and sex ratio of Ilisha africana off the Lagos Coast, Nigeria were investigated. Six macroscopic and seven microscopic stages of gonad maturity were identified. Maturity was attained at 12.0 cm total length. Breeding occurred throughout the year with the peak spawning between May and December. Oogenesis consisted of seven stages and breeding marks were observed in the species. Fecundity ranged between 2098 and 11 687 eggs. There was a slightly higher correlation between fecundity and weight than between fecundity and length. The egg diameter varied from 0.77 to 1.35 mm. The overall sex ratio was 1 male to 0.97 female. The females however predominated over the males during most months in the peak breeding period.     

Some aspects of the reproductive biology of Spratelloides gracilis (Schlegel) in the Ysabel Passage, Papua New Guinea

Fecundity, length at first spawning, spawning seasonality and ovarian development of Spratelloides gracilis were determined by examining preserved ovaries from fish captured over a 5-year period. Fecundity ( F ) was estimated from the number of eggs in the most advanced ovarian mode and was related to fish length ( L ) by the function: log_e F =3.764 log_eL-7.308, and to weight ( W ) by: log_eW= 1.210 log_eW+7.337. Spawning was observed in most months of the year without any recognizable pattern between the years. Ova diameter frequencies were bimodal but the smaller mode remained stationary regardless of the position of the larger mode. This was interpreted as evidence that individual fish may spawn only once. From data on egg length versus fish length and gonad index versus fish length it was estimated that fish were first capable of spawning at 45 mm (fork length).     

Seasonal fluctuations in the riverain invertebrate fauna of the Blue Nile near Khartoum

The physical conditions on the Blue Nile Bank near Khartoum and the seasonal succession of the invertebrate fauna are described. The fauna is dominated by beetles, mainly Carabidae, in the rainy season which coincides with the annual flood and by spiders, mainly Lycosidae, in the dry season. Climatically, the habitat is relatively mild and food is relatively abundant. The main problem with which the fauna has to contend is the annual rise and fall of the Nile.     

Some aspects of the reproductive biology ofBarbus spp.,Capoeta damascina and their hybrids (Cyprinidae, Teleostei) in Israel

The reproductive biology and gonad cycle of three Cyprinid fish species:Barbus canis (Valenciennes, 1842),B. longiceps (Valenciennes, 1842) andCapoeta damascina (Valenciennes, 1842), in the upper Jordan River system of Israel were studied by monthly sampling over a two-year period. The reproductive activity of the three species was found to peak from January to April, mostly involving upstream migration towards spawning grounds on river beds 400–900 m above the Jordan River. Hybrids of the three species were collected in nature: in those ofBarbus canis ×Capoeta damascina, the gonads possessed both types of gametes, spermatogonia and oogonia, all of which became arrested at an early stage of development, and infertile; in hybrids of detected in nature, males had oocytes dispersed in the testis, whereas in females, the ovaries had small islets of spermatogonial tissue. In these female hybrids the oocytes ripened normally and spawning occurred.     

Some aspects of osmotic biology of the freshwater leech,Poecilobdella viridis (Blanchard)

Ability of the freshwater leech, Poecilobdella viridis to withstand osmotic changes was investigated by following the fluctuations of the body weight in tap-water and in different salt concentrations. The salinity tolerance limit (lethal salt concentration) of this leech was found to be 1.54% NaCl which equilibrates approximately 51.359% sea-water. There was a significant weight loss in P. viridis when kept in both, hypo- and hypertonic media. It is concluded that volume regulation (through weight changes) was slight in hypotonic media whereas in hypertonic media there was an incessant decline in body weight. Adaptive significance of these findings is discussed.     

Interactions between Nile tilapia (Oreochromis niloticus) and cladocerans in ponds (Khartoum,Sudan)

Juvenile Nile tilapia (Oreochromis niloticus) are omnivorous, and the question asked in this study is how they affect on their environment? Do they mainly act as predators on the cladoceran zooplankton or do they compete with the cladocerans for phytoplankton? This problem was studied in three ponds with and three ponds without small tilapia (3–5 cm). The fish growth rate, the succession of plankton species and the changes in abiotic conditions, were monitored over a period of 67 days. The fish biomass was kept low and the mean was approximately constant (12.6 g m^?2) during the experiment. Phosphate was added to avoid phytoplankton nutrient limitation. Although the diet of Nile tilapia contained both phytoplankton and zooplankton, the fish affected the ecosystem in a similar way as zooplanktivorous fish. The fish ponds got more phytoplankton due to increase of Chlorophyta. Effects on the other phytoplankton groups Euglenophyta, Bacillariophyta, Cryptophyta and Cyanophyta could not be registered. The ponds without fish had higher densities of Daphnia lumholtzi and D. barbata. The other Cladocerans seemed less influenced by fish presence. The relative fish growth rate was most positively correlated with the density of Daphnia lumholtzi, Diaphanosmoa excisum and Bosmina longirostris. Tilapia seemes to have two feeding modes: (1) preying on large zooplankton and (2) unselective filtration of small planktonic organisms such as phytoplankton. In our experiment the first feeding mode affected the ecosystem more than the second.     

Some aspects of the reproductive biology of perch Perca fluviatilis L. A histological description of the reproductive cycle

Histological changes in the perch ovary during development are described and related to changes in gonad weight and to a macroscopic scale of maturity stages after Kesteven (1960). A single organ formed by the fusion of two primordial ovaries, a central internal oviduct, and an extremely thick chorion surrounding oocytes are characteristic features of the perch ovary. Resting oocytes can be differentiated from developing oocytes which are larger and possess a granulosa layer which permits formation of the chorion and yolk acquisition. In the maturing ovary, oocyte diameter increases rapidly and the chorion, which possesses four layers, the tunica propria, two middle zones forming a fine network, and the zona radiata, also expands. The spent ovary is disorganized with follicles and tunica wall contracted, and a number of residual oocytes may be apparent. There was no evidence of pre-ovulatory degeneration although autolysis of a small number of residual oocytes was observed. The gonadosomatic index was highest for males in September and at a maximum in females immediately prior to spawning. After spawning the index fell rapidly with lowest values recorded in June and July. Variations in the gonadosomatic index are related to developmental stages in females.     

Cephalodiscus reproductive biology (Pterobranchia,Hemichordata)

Sexually mature adults and embryos and larvae of Cephalodiscus nigrescens and C. gracilis were studied by light and electron microscopy. Contrary to claims in the literature, individual coenecial cavities are inhabited by colonies of up to 15 joined zooids and not by single individuals, which is important for the interpretation of the mode of life of the related fossil group the graptolites. Some aspects of the reproductive apparatus and reproduction in Cephalodiscus are reported. The ultrastructure of the spermatozoon is described for the first time. Coelom formation is by schizocoely. The structure of the larva at several developmental stages is illustrated. Not all fertilised eggs are destined to become motile larvae and some develop into zooids omitting the motile stage. The lumen of the oviduct is much larger than previously supposed. Spermatozoa are shed into the cavity of the coenecium. It is proposed that fertilisation takes place within the coenecium. The ultrastructure of the enigmatic black ‘Comma Body’ is described and a reproductive function is proposed. Budding takes place from a base common to several zooids. This base probably also serves as an attachment foot. Large masses of yolk have been discovered within the coelom of some zooids and muscle stalks. It is inconceivable that a colony of Cephalodiscus nigrescens could survive unless it spent most of its life outside the coenecium.     

Some aspects of the reproductive biology of perch Perca fluviatilis L. Fecundity, maturation and spawning behaviour

Fecundity of perch estimated from a regression of egg. number on fish length varied from 6711 for a fish of 14.5 cm to 77978 for a female of 34. 5 cm. Other independent variables related to egg number were age, gonad weight and somatic weight. Mean egg diameter varied from 0.94 to 1.62 mm. Males matured in their second year at a length of 6 cm and above while all females spawned at age four at a length of 15–18 cm. A proportion of females at Davan spawned one year earlier than at Kinord and were also slightly smaller on spawning. Faster growth of Davan fish may have encouraged earlier maturation. Spawning behaviour is described from film material.     

Selected aspects of female white-faced saki (Pithecia pithecia) reproductive biology in captivity

Little is known regarding the reproductive biology of the white-faced saki. Although sakis have been in zoos since the mid-1970s, little attention has been paid to the reproductive biology of this threatened species. This study describes the results of a 3-year study of the reproduction of the white-faced saki in captivity. Using noninvasive methods to determine levels of estrone conjugates (E₁C) and pregnanediol-3-glucuronide (PdG) in daily urine samples, we have characterized the female reproductive cycle of this species. Nonconceptive ovarian cycles were 16.95 ± 1.57 (SD) days, gestational length was 146.1 ± 5.2 (SD) days, and the length of lactationally induced infertility varied among females but averaged 163 ± 40.6 (SD) days. Attempts to accelerate puberty by pairing a young female with an adult male was without effect. Puberty occurred at 32 months of age in one female. This study provides information that enhances our understanding of the reproductive biology of this species. © 1995 Wiley-Liss, Inc.     

Growth in captivity and aspects of reproductive biology of the Antarctic fish parasite Aega antarctica (Crustacea,Isopoda)

Summary Specimens of the fish parasite Aega antarctica caught in the Weddell Sea and off the South Shetlands and South Orkneys were kept in aquaria for more than 2 years. These isopods were fed with plaice (Pleuronectes platessa) from the North Sea. Growth in captivity was very slow. For the first growth phase before reaching sexual maturity of females the value K = 0.12 was calculated for the Bertalanffy growth constant. Mature males are markedly smaller than breeding females (average lengths: 16.0 and 22.5 mm). An age of more than 5 years was calculated for an average-sized male, females spawn at an age of more than 10 years. No evidence for protandric hermaphroditism could be found.     

Some aspects of the biology of the garfish Belone belone (L.) from southern Ireland

An account is given of certain aspects of the biology of the garfish, Belone belone , captured by sea anglers from Courtmacsherry Bay, Co. Cork. Fish were aged by otoliths, and found to grow most rapidly in their first 2 years, females attaining a greater mean size than males. Most of the fish caught had already spawned. From examination of their gonads and lengths of juveniles collected in the neuston, spawning would appear to take place there mostly in the month of June.     

The reproductive biology of the genusBaldellia (Alismataceae)

The reproductive biology of the genusBaldellia was studied under cultivation and in nature.B. ranunculoides subsp.repens is self-incompatible whereasB. ranunculoides subsp.ranunculoides andB. alpestris are self-compatible. Bud-pollination occurs in theB. alpestris. Self-incompatibility correlates with the production of fewer, larger, more showy flowers, higher pollen production (but reduced pollen grain size), fewer carpels and smaller seeds. Resource allocation to sexual reproduction is inversely correlated with the degree of vegetative growth.B. ranunculoides subsp.repens produces more ramets than subsp.ranunculoides, which reproduces mainly by seeds.B. alpestris is intermediate between the two since it is self-compatible, produces fewer, larger seed than subsp.ranunculoides and is also able to propagate by vegetative means.     

Floral biology, reproductive system and reproductive success of Macroptilium fraternum (Fabaceae)

Observations about the floral biology and the reproductive system of Macroptilium fraternum were made in two populations in Argentina, with different edaphic conditions, situated at the southern area of distribution of the species. The coexistence of two kind of flowers in the same plant was detected in both populations and in herbarium material from other localities: a) cleistogamous preanthesis flowers and b) pseudocleistogamous flowers. The cleistogamous preanthesis flowers possessed wings longer than 5 mm and were disposed in pubescent, erect, racemes exposed above the level of the foliage. The anthesis lasted approximately 5 hours on sunny days or 9 hours on rainy days, the right wing covered the left wing, the corolla acquired a bilabiate aspect, offering the left wing as landing platform; they produced a low quantity of nectar (0.18 +/- 0.13 microliter); they did not receive pollinator visits; approximately four hours after the beginning of the anthesis on sunny days the ovary started to grow; in the bud, the receptive stigma was covered with germinating pollen grains from the same floral unit. The pseudocleistogamous flowers possessed wings shorter than 5 mm that were disposed in brief, hirsute and prostrate racemes, non subterranean as in other Macroptilium species; the banner started to spread exposing partially the wings, the left wing limb surrounded the keel and never spread; the right wing started to spread and after 2 seconds refolded and began to wither, the ovary began to grow immediately; the flower did not offer a surface to allow visitors to settle; in the buds the stigma was receptive and found with pollen grains from the same floral unit emitting their tubes. The relative reproductive success was low (natural pollination = 8%; spontaneous self-pollination = 3%), probably due to the low pollen viability, the high percentage of seed abortion and the lack of pollinator's visits. The production of both flower types is not conditioned by edaphic factors, as they were found in plants belonging to different environments. Study of the progeny of both floral types in both populations has demonstrated that each one produces a similar amount of seeds contributing to the next generation with plants of similar characteristics (slow development, low resistance to infections and high mortality). The absence of pollinators in these flowers (in part because they preferred to visit flowers of other species with more reward and in part because of the fragmentation of the habitats), would be producing inbreeding depression in the studied populations; if the germplasm variability is not preserved, these populations situated at the Southern end of the distribution range of the species could become extinguished.