Partial compensatory growth in hybrid tilapia Oreochromis mossambicus x O-niloticus following food deprivation

The capacity of hybrid tilapia Oreochromis mossambicus x O. niloticus [23.2 +/- 0.2 g (mean +/- SE)] to show compensatory growth was assessed in an 8-week experiment. Fish were deprived of feed for 1, 2 and 4 weeks, and then fed to satiation for 4 weeks; fish fed to satiation during the experiment served as control. Water temperature gradually declined from 28.1 to 25.5 degrees C throughout the experiment. Specific growth rate (SGR) decreased with progressive food deprivation. At the end of deprivation, body weight was lower in the deprived fish than in the control. Fish deprived for 4 weeks exhibited lower contents of lipids and energy in whole body, and higher moisture content and ratio of protein to energy (P/E) than those of the control; they also consumed feed faster than the control when normal feeding was resumed. All deprived fish showed higher food intake (FI) than that of the control during re-alimentation; however, enhanced SGR was only observed in the fish deprived for 4 weeks. There were no significant differences in digestibility of protein and energy, food efficiency (FE) or energy retention efficiency between the control and deprived fish. At the end of re-alimentation, deprived fish failed to catch up in body weight with the control, while content of moisture, lipids and energy, and P/E in whole body of the deprived fish did not significantly differ from that of the control. The results of the experiment revealed that the hybrid tilapia reared in freshwater showed partial capacity for compensatory growth following food deprivation of 4 weeks, and that growth compensation was due mainly to increased FI, rather than to improved FE.

Use of the aquatic protozoa to formulate a community biotic index for an urban water system

Protozoan were collected from 16 stations in water system of Changde City (China) using the PFU method. Sampling programs were conduced on a yearly basis, with seasonal frequency at diverse sites in the water system and 488 species of protozoa was identified. At the same time, Water sampling from these stations was conducted and various water chemical parameters, including DO, COD, BOD5, NH3, TP, and Volatile Phenol, were analyzed. The aim of the research was, on one hand, using chemical method to take an investigation to the water pollution status of Changde City; on the other hand, using protozoan to make an evaluation to the water quality. With the chemical water parameters and protozoa data, a biotic index was derived for the investigated region. The species pollution value (SPV) of 469 protozoa species was established, and the community pollution value (CPV) calculated from SPV was used to evaluate water quality. The method of the biotic index was tested and the result showed that CPV calculated from SPV had a close correlation with the degree of water pollution (p < 0.00001). This indicated that the method of the biotic index is reliable. The water quality degrees divided by CPV were suggested. (c) 2004 Elsevier B.V. All rights reserved.

Compensatory growth and food consumption in gibel carp, Carassius auratus gibelio, and Chinese longsnout catfish, Leiocassis longirostris, experiencing cycles of feed deprivation and re-feeding

The compensatory responses of juvenile gibel carp and Chinese longsnout catfish to four cycles of 1 part of a study designed to determine feeding regimes that would maximise growth rates. Both species showed compensatory growth in the re-feeding periods. The compensation was not sufficient for the deprived fish to match the growth trajectories of controls fed to satiation daily. The compensatory growth response was more clearly defined in the later cycles. The deprived fish showed hyperphagia during the 2-week periods of re-feeding and the hyperphagic response was clearer in the later cycles. The hyperphagia tended to persist for both weeks of the re-feeding period. The gibel carp showed no difference in gross growth efficiency between deprived and control fish. In the catfish, the gross growth efficiency of the deprived fish was marginally higher than that of control fish, but the efficiency varied erratically from week to week. Over the experiment, the deprived fish achieved growth rates 75-80% of those shown by control fish, although fed at a frequency of 66%. There was no evidence of growth over-compensation with the deprivation-re-feeding protocol used in this study. (C) 2004 Elsevier B.V. All rights reserved.

Development of a biotic index using the correlation of protozoan communities with chemical water quality

A method of comparing data on protozoan communities with chemical parameters is presented. Using data from an extensive survey of the River Hanjiang in China, each species of protozoa has been given a species pollution value (SPV) related to its occurrence in waters with different degrees of pollution. A comprehensive chemical index is calculated for each site based on water quality standards for eight chemical parameters. The index is calculated from the relationship between the observed levels of each chemical at a site, compared with the limits of the drinking water quality standards of the People's Republic of China. From the distribution of each species at sites with differing chemical index values, a SPV is calculated. The SPV for each species is obtained by summing the logarithmic value of 10 times the chemical pollution divided by the number of chemical parameters, then divided by the stations where the species occurs. The community pollution value (CPV), which is the average SPVs of all protozoa at a site, is used to evaluate water quality. The CPV has been shown to have a close correlation with the degree of water pollution. It is not necessary for all the protozoa in a sample to have SPVs listed in this paper, provided at least 56% of the protozoa in a sample have an SPV value, the CPV will be applicable.

Application and validation of a new biotic index using data from several water systems

Protozoans of Lake Donghu were collected from five stations using the PFU method. The sampling was conducted for one year and two times a month. The aim of this research was to test the applicability of a new protozoa biotic index, species pollution value (SPV) and community pollution value (CPV), established by the authors using data from the River Hanjiang. Each station's CPV was calculated from the SPV and the correlation analysis between the CPV and the comprehensive chemical index of stations I, II, III showed a significant correlation between them. The pollution status of the five stations was correctly evaluated by the CPV. These results suggested that the biotic index could be applied in water systems other than the River Hanjiang. The SPV of some protozoa species in Lake Donghu, not observed in the River Hanjiang were established. In order to further test the applicability of the biotic index, protozoan and chemistry data from the Rivers Torrente Stirone and Parma of Italy were used. The results showed that the CPV for the two rivers had a close relationship with the chemical water quality, which indicated that the biotic index could be applied in other parts of the world for the monitoring and estimating of water quality. Since the results of testing and verifying the biotic index in some other water systems in China were also satisfactory, this indicated that the biotic index has an extensive suitability for freshwater ecosystems. As long as more than 50% of the species in a sample have a SPV, the CPV calculated from the SPV is reliable for monitoring and evaluating water quality.

Effect of cycles of feed deprivation on growth and food consumption of immature three-spined sticklebacks and European minnows

Individual juvenile three-spined sticklebacks Gasterosteus aculeatus and European minnow Phoxinus phoxinus, from sympatric populations, were subjected to four cycles of I week of food deprivation and 2 weeks of ad libitum feeding. Mean specific growth rate during the weeks of deprivation was negative and did not differ between species. The three-spined stickleback showed sufficient growth compensation to recover to the growth trajectory shown by control fish daily fed ad libitum. The compensation was generated by hyperphagia during the re-feeding periods, and in the last two periods of re-feeding, the gross growth efficiencies of deprived three-spined sticklebacks were greater than in control fish. The expression of the compensatory changes in growth and food consumption became clearer over the successive periods of re-feeding. The European minnow developed only a weak compensatory growth response and the mass trajectory of the deprived fish deviated more and more from the control trajectory During re-feeding periods, there were no significant differences in food consumption or gross growth efficiency between control and deprived European minnows. The differences between the two species are discussed in terms of the possible costs of compensatory growth, the control of growth and differences in feeding biology (C) 2003 The Fisheries Society of the British Isles.

Compensatory growth response in three-spined stickleback in relation to feed-deprivation protocols

Different protocols of food deprivation were used to bring two groups of juvenile three-spined sticklebacks Gaslerosteus aculeatus to the same reduced body mass in comparison with a control group fed daily ad libitum. One group experienced I week or deprivation then 2 weeks on maintenance rations. The second group experienced I week of ad lithium feeding followed by 2 weeks of deprivation. The deprived groups were reduced to a mean mass ore. 80% of controls. The compensatory growth response shown when ad libitum feeding was resumed was independent of the trajectory by which the three-spined sticklebacks had reached the reduced body mass. The compensatory response was Sufficient to return the deprived groups to the mass and length trajectories shown by the control group within 4 weeks. There was full compensation for dry mass and total lipid, but incomplete compensation for lipid-free dry mass. Hyperphagia and increased growth efficiency were present in the re-feeding phase, but there was a lag of a week before the hyperphagia was established. The consistency of the compensatory response of immature three-spined sticklebacks provides a potential model system for the analysis and prediction of appetite and growth in teleosts. (C) 2003 The Fisheries Society of the British isles.

Compensatory growth in the gibel carp following feed deprivation: temporal patterns in growth, nutrient deposition, feed intake and body composition

To investigate the nature of compenstory growth in fish, an 8 week study at 28 degreesC was performed on juvenile gibel carp Carassius auratus gibelio weighing 6.6 g. Fish were starved for 0 (control), 1 (Sl)or 2 (S2) weeks and then re-fed to satiation For 5 weeks. Weekly changes in weight gain, feed intake and body composition were monitored during re-feeding. No significant difference was found in final body weight between the three groups, indicating complete compensation in the deprived fish, The deprived groups caught up in body weight with that of the control after 2 weeks of re-feeding. Body fat:lean body mass ratio was restored to the control level within 1 week of re-feeding. In the re-feeding period, weekly gains in body weight, protein. lipid, ash and energy in the S1 group were significantly higher than in the controls for 1 week. For the S2 group, weekly gains in body weight. lipid. ash and energy were higher than in the controls for 2 weeks, and gain in protein was higher than in the controls for 3 weeks, though gain in body energy became elevated again during the last 2 weeks of the experiment. Feed intake remained higher than the control level for 3 weeks in the S1 group and 3 weeks in the SZ group. Growth efficiency was not significantly different among the three groups in any of the weeks during re-feeding. Compensatory responses in growth and especially feed intake tended to last longer than the recovery of body composition. (C) 2001 The Fisheries Society of the British Isles.

Comparison of compensatory growth responses of juvenile three-spined stickleback and minnow following similar food deprivation protocols

The compensatory growth responses of individual juveniles of two co-existing species were compared after identical periods of starvation to determine inter-specific similarities and differences. The carnivorous stickleback Gasterosteus aculeatus was compared with the omnivorous minnow Phoxinus phoxinus. Both species experienced 1 or 2 weeks of starvation before being re-fed ad libitum. The two species differed in their response to the starvation periods, with minnows showing a lower weight-specific loss. Both species showed compensatory responses in appetite, growth and to a lesser extent, growth efficiency. Minnows wholly compensated for 1 and 2 weeks of starvation. At the end of the experiment, sticklebacks starved For 2 weeks were still showing a compensatory response and had nut achieved full compensation. The compensatory responses of the sticklebacks showed a lag of a week before developing in the re-feeding phase, whereas the response of the minnows was immediate. Analysis of lipid and dry matter concentrations suggested that the compensatory response restored reserve lipids while also bringing the fish back to the growth trajectory of continuously fed fish. (C) 2001 The Fisheries Society of the British Isles.

Compensatory growth, feed utilization and activity in gibel carp, following feed deprivation

Following a period of food deprivation, gibel carp compensated for growth through increased feed intake and conversion efficiency, but increased conversion efficiency was not achieved by increasing digestibility or reducing activity. (C) 2000 The Fisheries Society of the British Isles.

A ridge width varied two-section index-coupled DFB self-pulsation laser with a wide continuously tunable frequency range

A 1.55 mu m InGaAsP-InP index-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. A record wide self-pulsation tuning range above 450 GHz has been achieved for this index-coupled DFB SPL. Furthermore, frequency locking to an optically injected modulated signal is successfully demonstrated.

Fabrication and performance of an index-coupled DFB laser with sampled grating

An index-coupled DFB laser with a sampled grating has been designed and fabricated. The key concept of the approaches is to utilize the +1st-order reflection of the sampled grating for laser operation, and use a conventional holographic exposure combined with the usual photolithography to form the sampled grating. The typical threshold current of the sampled grating DFB laser is 25 mA, and the optical output is about 10 mW at the injected current of 100 mA. The lasing wavelength of the device is 1.5314 mu m, which is the +1st-order peak of the sampled grating.

Measurement of chirp parameter and modulation index of a semiconductor laser based on optical spectrum analysis

A novel and simple method for measuring the chirp parameter, frequency, and intensity modulation indexes of directly modulated lasers is proposed in a small-signal modulation scheme. A graphical approach is presented. An analytical solution to the measurement of low chirp parameters is also given. The measured results agree well with those obtained using the conventional methods.

Estimation of frequency response of directly modulated lasers from optical spectra

A simple method for estimating the frequency responses of directly modulated lasers from optical spectra is presented. The frequency-modulation index and intensity-modulation index of a distributed feedback laser can be obtained through the optical spectrum analyses. The main advantage is that the measurement setup is very simple. Only a microwave source and an optical spectrum analyser are needed and there is no need to use a calibrated broadband photodetector. Experiment shows that the proposed method is as accurate as the swept frequency method using a network analyzer and is applicable to a wide range of modulation powers.

A highly efficient beam propagation method for modeling step-index waveguides with tilt interface

Based on a new finite-difference scheme and Runge-Kutta method together with transparent boundary conditions (TBCs), a novel beam propagation method to model step-index waveguides with tilt interfaces is presented. The modified scheme provides an precies description of the tilt interface of the nonrectangular waveguide structure, showing a much better efficiency and accuracy comparing with the previously presented formulas.