摘要:

The effectiveness of methyltestosterone (MT) for sex reversal and growth promotion inOreochromis mossambicuswas studied in culture experiments in India. Wild‐spawned fry were treated with 30 μg MT g−1diet for 30 or 60 days at two feeding levels (initially 20% or 10% of body weight daily). The fish were grown on for 66–96 days after the hormone treatment period in fertilized cement ponds without supplementary feeding. Tilapia treated with MT for 60 days attained an average weight of 29.0 g compared to 18.8 g for untreated fish reared under similar conditions. The percentage of males among the untreated tilapia was 58%, MT treatment for 30 days significantly increased this percentage at the higher feeding level (79% male), but not at the lower feeding level (51%). More than 90% of the tilapia in both 60 day MT treatment groups were male; 3% of all the fish reared showed an intersex condition. The experiments demonstrated that the anabolic and sex reversal effects of MT on tilapia are proportional to the duration of treatment and quantity of hormone administered. The possible application of monosex tilapia culture in tropical countries is

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04245.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A study of growth curves of common carp of the Chinese and European races was aimed at gaining more understanding of the genetic and developmental interrelations between growth and sexual maturation. A negative association between growth rate and onset of sexual maturity was noted particularly in the Chinese race. Gonad development in males of the Chinese race is faster, and starts earlier, than that of the European race. The Chinese x European crossbred shows incomplete dominance in the direction of the European parent for this trait. Heterosis for growth under harsh conditions (as of the Chinese parent) and slow sexual development (as of the European parent), acting together, result in over–all heterosis of the Chinese x European crossbre

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04246.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The occurrence in the North Sea of a specimen of the white pomfret,Pampus argenteus(Euphrasen, 1788), a mesopelagic fish which is native to the Indian Ocean and particularly South‐east Asia and the East China Sea, is described. Other anomalous distribution records for the same species are examined and some possible explanations investigate

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04247.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Stepwise regression models utilizing five easily‐measured condition indices, two physiological variables and two environmental variables were developed for estimating the monthly growth of age‐I and II largemouth bass sampled during 1980 and 1982. The liver‐somatic index (LSI) and standard metabolism at surface and thermocline temperatures were the most significant variables for estimating growth. Determination of monthly growth using the LSI requires 50% fewer samples than the usual method of following changes in monthly mean weight. Because the LSI responds relatively rapidly to levels of energy intake and temperature, this index can be used to signal possible adverse effects on fish before changes in growth can be observed. This approach could be a useful management tool because, once validated for a particular aquatic system, frequent cost‐effective growth estimates could be used to identify the presence of ecological perturbations and to quantify their

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04248.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Juvenile cod (Gadus morhua)were made to swim in a tunnel respirometer to determine the oxygen consumption during swimming at different speeds. Results were compared with measurements of standard and active metabolic rates in static respirometers before and after intense exercise. The oxygen consumption at maximum sustainable swimming speed was considerably lower than the peak oxygen consumption following exhausting exercise. It is suggested that these fish have a poorly developed system of aerobic (red) locomotor muscles which do not normally make a major demand upon oxygen consumption. Apparent specific dynamic action following feeding and repayment of oxygen debt following anaerobic exercise can each give rise to greater rates of oxygen consumption. Following exhausting exercise there is a delay of about 1 h before oxygen consumption reaches a peak level some 40% higher than the peak level observed during sustained swimming.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04249.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Performance of two larval fish samplers, a hand–towed net and a dropbox enclosure, was similar when tested in shallow (x water depth, 20 cm) upper littoral–zone habitats. There was no significant difference between means of larval fish density (by total catch and by species) estimated from the catch in each gear, during the day and at night. Mean length of larvae (total catch) from the tow net was significantly longer than that from the dropbox during the day, but mean length did not differ between gear at night. Mean lengths of larvae of each species between gear were not significantly different within each period. Both gears collected significantly longer larvae (total catch and by species) during the day than at night probably because of diel movements of larvae of different sizes and spec

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04250.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04251.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

In a study following growth and food intake of individuals within a population it was important to obtain individual rather than group mean measurements. A technique is described which combined the benefits of X‐ray readable microtags with the radiographic method for measuring food intake described by Talbot&Higgins (1983). Its usefulness was established in an eight–month study on hatchery reared juvenile Atlantic salmon,Salmo sal

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04252.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Plasma osmotic regulation was evaluated inCyprinodon variegatusacclimated to salinities from fresh water to 120%. These fish showed roughly stable regulation in the range from 0.3% to 70%. Fish acclimated to fresh water showed an increased plasma concentration over those in 0.3%, thought to result from a higher Ca++level in fresh water. Plasma concentrations rose abruptly at salinities above 70%. Osmotic regulatory characteristics ofC. variegatuswere compared with data for other extremely euryhaline species with expectation of a graded series of responses, species showing greatest fresh water tolerance demonstrating widest ranges of regulation and with lowest plasma concentrations. Results were not consistent with expectations. The range of ambient salinities over which good regulation of plasma concentration was shown was found to be directly correlated with the magnitude of the salinity tolerance range of all of the species compared. Forms with greater fresh water affinity generally, but not uniformly, showed the lowest plasma concentrations in the region of hyperosmotic regulation.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04253.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A postprandial increase in ammonia nitrogen excretion and oxygen consumption rates was observed in juvenile pike fed a natural diet or an artificial dry diet. Specific growth rate of natural diet fed pike (2.4%) was lower than that of pike fed the artificial diet (3.1%). Fifty per cent of ingesta was evacuated within 5–6 h in pike of 25 mg body weight and 9–10 h in those weighing 150mg. Daily nitrogen excretion rates were related to body weight. Respiratory quotient and energy retention efficiency were affected by the nature of the diet ingested by pike. Parameters of the energy balance (losses, retention, increment due to feeding) were related to energy int

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04254.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY