摘要:

Diets of metamorphosing larvae and early juvenile summer and southern flounder were examined during the settlement period when their distributions overlapped and during a subsequent period when the two flounders were found in different habitats. Prey abundance on tidal flats was examined along an upstream transect. Though initially similar, diets of the two species diverged prior to the development of a segregated distribution. These diet differences reflected those found in the diets of the two species following segregation. Southern flounder ate more active epifaunal prey: mysids, amphipods and calanoid copepods and appeared to be an ambush predator. The summer flounder ate primarily infauna: polychaetes, and invertebrate parts and appeared to be an active forager. Distribution of prey within the study area suggested that mysid gradients may influence movement of southern flounder to nursery grounds. The coupling of biotic and abiotic gradients are probably important in creating nursery areas and guiding fishes to species specific habitat types.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01905.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The eye ofRhinomugil corsulahas a duplex retina differentiated into dorsal and ventral halves, with the ventral retina 116·4 μm thicker than the dorsal retina. The rods of the ventral retina are relatively longer, with longer outer segments. The nuclei of the outer nuclear layer of the dorsal and ventral halves are in four and six to seven rows respectively. The rod outer segment bears a single incision. The mitochondria of cone and rod inner segments has a vitreal‐scleral gradient. Single and double cones are present in both halves, with triple cones in the dorsal half only. The outer segments of double cones are equal and united. The single cones have two connecting cilia. The cone cells are arranged in a square mosaic with four double cones and five single cones to each unit in the dorsal half, and in a rhombic pattern in the ventral h

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01906.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

This study tests whether or not post‐exercise oxygen consumption rates (Mo2) in fish are dependent upon how exhaustion is induced. A group of eight Atlantic cod (Gadus morhua) were each exercised using (1) a critical swimming speed (Ucrit) protocol, (2) an exercise protocol designed to measure anaerobic capacity of fish (Uburst), and (3) a protocol in which the fish were chased to exhaustion manually.Mo2was measured for a 2‐h period following exhaustion induced by all three exercise regimes (Ucrit,Uburstand chase). Post‐exerciseMo2following exhaustion from theUburstand chase protocols were significantly higher than post‐exerciseMo2following theUcritprotocol. Each fish during theUcritprotocol exhibited maximalMo2during exercise rather than during recovery, yet 75% of the fish duringUbrustrecovery and 100% during chase recovery exhibitedMo2higher than that measured duringUcritexercise. These results, as well as the large interindividual variations inMo2among the eight fish, show that post‐exhaustionMo2is specific to the exercise regime employed, thus, investigators must exercise caution when combining results from different exercise protocols and/or in

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01907.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Groups of fathead minnowsPimephales promelaswere tested to determine if they avoided areas of a test tank labelled with the faeces of a predator (northern pike,Esox lucius) which had recently been fed minnows, brook sticklebacksCulaea inconstans, or swordtailsXiphophorus helleri.Minnows exhibited a fright reaction upon presentation of sponges labelled with faeces, when the pike had consumed minnows or sticklebacks, but not swordtails (which lack alarm pheromones). The fright reaction was characterized by increased shoal cohesiveness and increased dashing and freezing behaviour. Minnows avoided the area of the tank containing the faeces from pike on diets of minnows or sticklebacks, but not from pike fed a diet of swordtails. These data demonstrate that: (1) minnows actively avoid the faeces of pike fed minnows or brook sticklebacks, and (2) minnows exhibit a fright reaction to the faeces of a pike fed brook sticklebacks.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01908.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effects of sex steroids on sex differentiation in the European eel were studied. The steroids, 17α‐methyltestosterone (MT) and 17α‐ethynylestradiol (EE), were given in the diet to 6–8 cm elvers and to 15–18 cm and 22–25 cm yellow eels. In our rearing conditions a very large percentage of the untreated eels developed as males. No masculinizing effect of MT could be demonstrated. The EE, administered at a dose of 10 mg kg‐1of diet to 6–8 cm elvers and 15–18 cm eels, induced ovarian differentiation in about 90 and 65% of eels respectively, while in the control<5% of females was recorded. In 22–25 cm yellow eels a moderated feminizing effect was observed.Histological analysis of the gonads of treated eels showed that sex steroids affect the gonadal structure. The androgen stimulates hypertrophy of compact connective tissue, early differentiation of Leydig cells, Sertoli cells and early formation of the spermatic duct. Oestrogen inhibits the differentiation of these structural components and stimulates the differentiation of follicular cells and an ovarian structure.The involvement of gonadal structural components is discussed in relation to the effect of steroid treatment and to the peculiarities of sex differentiation

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01909.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The fry ofLiza ramada, L. aurata, L. saliens, Chelon labrosus and Mugil cephalusin a lagoon in NE Spain fed mainly on zooplanktonic crustacea, such as cyclopoids, calanoids and cladocerans, but adult chironomids were also important. A high trophic and temporal overlap was found between the fry of several of these species. Trophic overlap was asymmetrical for almost all the species pairs and niche breadth expanded for the less competitive species when they were alone in the estuary. In contrast, niche breadth did not expand for the most competitive species (L. ramada) when it was alone. These results suggest that competition was occurring among these species, but experimental evidence is needed to prove its existence.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01910.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Aspects ofScyliorhinus caniculadistribution in the North Aegean Sea are reported. Data were collected during four seasonal trawl surveys carried out in 1991. The pattern of vertical distribution of the individuals did not exhibit any sexual segregation. In contrast to Springer's hypothesis, juveniles and adults were found together on the bathyal bottoms.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01911.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Development of the liver in sea bream,Sparus aurata, was studied using light and electron microscopy from hatching to the age of 23 days. Histochemical reactions were used to monitor changes in lipids and glycogen during this period. During the strictly endotrophic prelarval phase from hatching until mouth‐opening, the primordial liver formed by budding on the gut wall and became organized in contact with the vitelline vesicle. The initially undifferentiated cells rapidly polarized and became pyramidal in outline with their apical extremities terminating in cavities corresponding to the future bile canaliculi. Sinusoids formed centripetally. Glycogen was stored in the cytoplasm of differentiating hepatocytes. At the beginning of the larval stage the hepatocytes multiplied, bile canaliculi were completed and the sinusoids acquired their final form. Glycogen reserves decreased strongly as bile secretion started. The end of the endo‐extrophic period was marked by distinct recovery of glycogen storage, synthesis of numerous lipoproteins and discharge into the sinuso

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01912.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The histological effects of cyanide, stress and starvation on the gastrointestinal tract ofPomacentrus coelestis, a common marine aquarium fish species, were investigated. Neither anaesthetic cyanide nor stress were found to have any detectable effects on the mucosal lining of the intestine. However, starvation resulted in a significant reduction in the intestine length, the surface area of the intestinal mucosa and the mucosal thickness, all occurring within 13 days.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01913.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

There were significant differences among five sympatric herbivorous reef fish species in their ranking of seven food‐processing characters. Between themZebrasoma scopasandStegastes nigricanshad the lowest bite rates, longest filling times, lowest defaecation activities and slowest gut turnover.Acanthurus nigrofuscusandScarus sordiduswere similar in having the fastest filling times, and high bite rates, gut‐contents masses, gut turnover and defaecation activities.Ctenochaetus striatuswas intermediate between those species pairs in five out of seven characters. Rich algal diets ofS. nigricansandZ. scopaswere contrasted with the carbonate intake ofS. sordidus. The food‐processing pattern ofC. striatuswas related to the siliceous content of a diatom diet. Food‐processing characteristics ofA. nigrofuscuswere attributed to a diet which is readily absorbed and/or is of high nutritional

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01914.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY