摘要:

Sandbar sharks maintained in an enclosure in the natural environment were fed meals of soft blue crab,Callinectes sapidus, or menhaden,Brevoortia lyrannus, and were sacrificed at intervals after feeding to measure rates of gastric emptying. Regression analysis was used to evaluate the adequacy of various models in describing the decrease in stomach contents with time after feeding. A Gompertz growth curve provided the best fit to the data for both food types. This model suggests that gastric emptying is characterized by an initial lag phase during which evacuation rate increases, a period of maximal evacuation, and a decreasing evacuation rate during the later stages of digestion. Passage of food from the stomach was slow relative to other species of fish studied. The time required to evacuate 98% of a meal was 92–3 and 70–7 h for sharks fed menhaden and blue crab respectively. Evacuation rates did not differ between day and night peri

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04263.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The levels of chitinolytic enzymes and chitinolytic bacteria in the digestive tract of feeding and fasting cod were compared. Enzyme activities within a given tissue were of a similar order irrespective of the presence of chitinolytic bacteria and/or chitin. Cod chitinase and chitobiase are therefore endogenous and constitutive enzymes. Fasting cod had similar numbers of bacteria within the gastro‐intestinal compartments as feeding fish. Representative bacterial isolates from fasting fish were characterize

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04264.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A method is described which has broad application for field acquisition of fish karyotypes for research and teaching. The benefits of the method include: low initial skill level, relatively inexpensive equipment and supplies, simplicity and speed, and the high quality of preparations. The technique was applied to a field study ofApogon maculatuswhich was shown to contain 34 chromosomes, 2 nucleolar organizing regions (NOR's), and resolvable G‐band

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04265.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Of 13 nemipterid species from coastal waters around northern Australia, nine show size‐related differences in sex ratio with males predominating at larger sizes. Histological examination of gonads shows that inScolopsis monogramma S. taeniopterusandS. bilineatusthis size‐related skew in sex ratio results from protogynous hermaphroditism and not from sexually differentiated growth rates as has been reported for other nemipterid species. There is also evidence that, in two other species,Nemipterus peroniiandPentapodus porosus, hermaphroditism may occur. Although the mechanism by which the gonads are transformed inS monogrammaandS. taeniopterusdiffer markedly, there is evidence to suggest that in both species sex change is a post spawning event, successful initiation of which may require females to have achieved an advanced stage of vitellogeni

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04266.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The capture of a specimen ofLaemonema latifromHolt&Byrne, 1908, off Blanes (western Mediterranean) at a depth of 550m, in December 1983, is reported for the first time in this region.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04267.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Juvenile steelhead trout,Salmo gairdneriinjected with thyroxine (T4) near the time of seaward migration exhibited a significantly lower migration tendency than untreated controls of fish injected with saline, thiourea, or a combination of T4and thiourea. Fish injected with thiourea alone or in combination with T4prior to the time of maximum migration tendency showed enhanced migration over untreated and saline injected controls and those injected with T4alone. Injections of T4or a combination of T4and thiourea elevated plasma T4and tri‐iodothyronine (T3) concentrations, while injection of thiourea alone depressed thyroid hormone levels relative to saline‐injected controls. Plasma concentrations of T3and T4returned to control levels within 10 days in all groups. We suggest that thyroid hormones are antagonistic to mechanisms underlying seaward migration of steelhead trout and that these antagonistic effects must be overcome before migration tendency is expres

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04268.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Yellowfin bream,Acanthopagrus australis, of all age classes were collected from Moreton Bay, Australia. The species possessed typical sparid ovotestes in which the testis and ovary occur in separate zones. During the spawning period (June‐August) juveniles, functional males and functional females could be distinguished by the macroscopic appearance of the gonad. The sex ratio of males to females decreases with age, indicating protandrous sex inversion.Histological and structural study of the ovotestis showed all fish have previtellogenic cells in the ovarian zone but only juvenile and male fish have developing spermatogenic cells in the testis. Most juveniles become functional males by the age of two years but a small proportion of juveniles develop directly into functional females (primary females). Protandrous sex inversion commences after the spawning period when male fish appear with spermatozoa and no other spermatogenic cells in the testis. During the period November‐January male fish with no spermatogenic cells are common and a reduction in size of the testis occurs so that by March‐April the ovotestis becomes structurally and histologically similar to the female ovotestis. Some fish remain functional males during their whole life‐history (primary males). In functional females vitellogenic cells are present in the ovary only during the spawning period and the testis remains very small

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04269.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The material comprised 1205 arctic charr caught by gillnets and electrofishing in the ice‐free season 1982 in four interconnected lakes. The lakes were similar in biotic and abiotic factors and the arctic charr populations were therefore treated as one population. Two size groups of fish older than three years, called ‘small charr’ and ‘large charr’, were found. The two groups differed in feeding habits, growth rates, age of maturity and spawning frequencies. However, they did not differ in the frequencies of the F‐ and S‐ serum esterase alleles, and were in accord with the model proposed by Johnson (1976) which states that the ‘small charr’ and ‘large charr’ are two different forms of the same population. ‘Small charr’ recruit to the ‘large charr’ by entering a period of fast growth. In the investigated lakes this occurred when the ‘small charr’ were 3–10 years old. Some indications of rematuration of the ‘small charr’ when enterin

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04270.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Three thermal levels were tested on 10‐day oldT. zillifry obtained from one spawning to study the effects of temperature on the occurrence of growth depensation in the population reared under controlled environmental conditions. Results showed highest individual growth rate, mortality rates and growth depensation at 30 °C whilst the greatest biomass increase was obtained at an intermediate temperature (27 °C). The enhanced depensation and high mortality rates at the upper limit of the thermal gradient for growth ofT. zilliwere attributed to an alteration in the behaviour of fish which favoured a few, large, dominant and socially aggressive individu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04271.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Gastric emptying time inScophthalmus maximus, when fed friable artificial pellets based on fishmeal, is composed of two phases:(a) a delay time (td) during which the meal forms a bolus and which shortens with temperature, and(b) an emptying phase (durationtend) which varies with meal size (S), body weight (W) and temperature (71 according to:(wheretendis in h,Sis in g,Wis in g andTis °C). During the emptying phase, stomach contents decrease curvilinearly according to:(whereSt,&Sois in g andtis in h) in which the instantaneous digestion rate,K, varies with fish weight and temperature as:Food pellets were prepared which remained separate and did not form a bolus in the stomach;Kincreased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets,Kdecreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs atc.85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two‐thirds of the previous rate since stomach fullness, and hence digestion rate (g h−1), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g−1increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy‐rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and f

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04272.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY