ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05736.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The specific differences between the testis, milt and sperm of six species of tilapia includingOreochromis aureus, O. mossambicus, O. niloticus, Tilapia zillii, O. nilolicus×O. aureushybrid and red tilapia,Oreochromissp., were studied. The shape of testis is tubular; the gonadosomatic index varied from 0.07 to 2.71. The pH values of individual milts ranged from 6.2 to 8.2 and the osmolarity from 240 to 380 mOsmol kg−1. The quantity of milt obtained by stripping averaged only about 0.3 ml, and only in theO. niloticus×O. aureushybrid did it exceed 3 ml. Sperm motility graded from weak to moderate was determined for the stripped tilapia milt. Sperm concentrations ranged from 7.70 × 108sperms ml−1inT. zilliito 2.74 × 1010sperms ml−1inO. mossambicus. Tilapia sperm was active in various salinity ranges such as 0–5‰ forO. niloticus, and 0–15‰ forO. mossambicusandT. zillii.Extender containing 15% milk and 5% methanol was used to prepare milt mixture before cooling rapidly to −35° C and then at 5° C min−1to −75° C for storage in liquid nitrogen (– 196° C).Fertility tests on frozen tilapia milt resulted in a fertilization rate of 72.7% (v. control 85.7%) for the 22‐day frozen milt of theO. nilolicus×O. aureushybrid used to fertilize the eggs of O.honorum, and 93.4% (v. control 90%) for the 304‐day frozen sperm of red tilapia use

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05737.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Pennate diatoms, especiallyAslerionellaspp. andTabellaria fenestrata, were the most important food items for smelts in Lake Mjøsa during the first month of external feeding; rotifers and early stages of copepods were eaten occasionally. Later, during summer and autumn, crustacean zooplankton (cladocerans and copepods) were the most important food items; selected species werePolyphemus pediculus, Eudiaptomus gracilis, Limnocalanus macrurus, Heterocope appendiculata. Leplodora kindti, andBythotrephes longimanus; some smelts larger than 7.4 cm fed onMysis relicta. In 1979 and 1980, mean lengths of smelts in October‐November were 4.7 cm and 7.2 cm, respectively. A difference in length increment between the two years may have resulted from summer water temperatures being higher in 1980 than in 19

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05738.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Lake Kariba is thermally stratified for about 9 months of the year. The Tanganyika sardine,Limnothrissa miodon(Boulenger), thrives very well when the water is in circulation and when its food (zooplankton) is abundant due to increased nutrients in the water column. There is a fall in the sardine yields as the water column gets partitioned into a nutrient‐poor epilimnion and a nutrient‐rich hypolimnion during thermal stratification. A very high negative correlation (r2= 0.94,n= 32) was found between thermal stratification and the monthly yields of the sardines. This uneven annual distribution of sardine yields creates problems for the local fish

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05739.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The anatomy and the histology of the digestive tract of young and adult sea‐bream is described from studies using light and scanning electron microscopy. The dentition in the juvenile (25–30 mm long) comprises all canine‐like teeth, to which plate teeth and transition elements are added in the adult.The oesophagus shows a multi‐layered mucosa in the upper part, and single‐layered regions in the lower part. The multi‐layered regions are formed by epithelial cells, mucus‐secreting cells and by cells rich with eosinophilic granules.The Y‐shaped stomach, clearly distinguishable, has a single‐layered columnar epithelium under which, in the cardiac and fundic portion, gastric glands, comprised of all similar cells, are present. The pyloric region is characterized by four caeca, to the base of which the ductus pancreaticus and the ductus hepaticus discharge.The pancreas is composed of small masses spread along the upper intestine; in the adult, pancreatic infiltrations can be seen in the liver.The intestine is short (relative length 0.5–0.6). The intestine epithelium consists of columnar cells intercalated with mucus‐secreting cells. A funnel‐like valve marks the passage to the intestine terminal region, characterized by a mucosa of cells with an abundance of vacuoles full o

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05740.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The gut contents of 37 species of R. Nile fish are described. Classification according to diet shows four species to be mud‐feeders, three to be microherbivores, two to be macroherbivores and five to be omnivores. The remaining majority (23) are categorized as carnivorous and comprise one neuston‐feeder, one zooplanktivore, six bottom‐feeders, seven browsers in vegetation and eight macropredators. Food webs are proposed for three major ecological zones, namely the open‐water and submerged vegetation of a river‐lake, the floating fringe ofEichhornia crassipesand the seasonally flooded

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05741.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The post‐larval growth of lateral white muscle was studied in eels at different stages of post‐larval development (glass, yellow and silver eels) by means of histochemical methods for myosin‐ATPase (mATPase) activity, immunohistochemistry (for myosin isoforms) and electron microscopy.Morphological, histo‐ and immunohistochemical data reveal a uniform appearance of white muscle in glass eels, whereas in following stages the typical mosaic appearance is present. Small‐diameter fibres show a more acid‐labile mATPase activity than large fibres and react with anti‐F, anti‐FHC and anti‐S sera, but not with anti‐SHC serum. In the silver stage, the small fibres tend to decrease in number as the size of the eels increases.Electron microscopy reveals the presence of satellite cells at every stage: in glass eels there are also ‘activated’ elements showing scarce myofilaments in their cytoplasm; in yellow eels very small fibres are present, enveloped within the basal lamina of well‐differentiated muscle fibres; in silver eels there are no fibres showing signs of immaturity.Presumably the post‐larval development of white muscle involves in juvenile eels a substantial recruitment of fibres from the satellite cell population; later the hyperplasia decreases or ceases and hypertrophy remains the only

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05742.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Larval sea lampreys,Petromyzon marinus, of the 1976 year class were studied between May 1977 and October 1981 in five Michigan streams to determine the relationship of density to growth and metamorphosis. Two cages were placed in each stream; one cage contained 25 larvae (low density group) and the other 75 larvae (high density group). Changes in body length, as an indicator of growth, were monitored in all streams from age I to V. Mean lengths ranged from 25 to 55 mm at the beginning of the study and from 102 to 158 mm at the end. Some ammocoetes attained lengths greater than 160 mm. Growth was related mainly to density; crowding affected growth from age I to metamorphosis. Mean increases of total length ranged from 90 to 128 mm among low‐density groups and from 54 to 97 mm among high‐density groups. Growth was typically greater in the cage with fewer lampreys in each stream. Most growth occurred from May to October when stream temperatures were highest. In two streams in which cages were not vandalized, 96% and 92% of the lampreys in the low‐density groups and 68% and 52% in the high‐density groups survived to age V. Metamorphosis occurred at age V in low‐density groups. Five lampreys (2.4%; range, 133–145 mm long) metamorphosed among the 207 that survived until completion o

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05743.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The growth and feeding habits of juvenileClarias anguillaris(Linné 1762) during their 5‐month residence in the floodplain pools of the Sokoto‐Rima river basin are described. A mean growth increment of 202 mm and 69.7 g attained in the October to March season compares favourably with first‐year growth recorded for otherClariasspecies. The diet ofC. anguillarisis relatively unspecialized and includes a wide variety of items ranging from algae, higher plant material and detritus through larval dipterans, rotifers and copepods, to fish. There is variation in the diet according to month of capture and capture location, and a reduction in diet diversity with fish size. The findings are discussed in the context of work carried out on otherClariasspecies. It is proposed that C.anguillarisis suitable for locally operated fish culture prog

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05744.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Reproductive cycles were investigated in orange roughy,Hoplostethus atlanticus, smooth oreo,Pseudocyttus maculatus, and black oreo dory,Allocyttussp., from mid‐slope waters (600–1300 m) around New Zealand from 1982 to 1985. Orange roughly displayed a mid‐winter spawning period in July and August, whereas both dory species spawned in November and December. In all three species, the timing of spawning was consistent from year to year. Ovarian development in orange roughy and black oreo dory was found to be synchronous, with a single clutch of oocytes being matured for each spawning season. In males, testes of a given macroscopic stage were dominated by a single gamete stage, supporting the existence of a brief rather than prolonged spawning period. The possible relationship of spawning period to seasonal changes in the productivity of the surface water is disc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1987.tb05745.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY