Age estimation of juvenile European hake Merluccius merluccius based on otolith microstructure analysis: a slow or fast growth pattern?

The main goal of this study was to examine otolith microstructure and to estimate the age and growth of European hake Merluccius merluccius from the eastern Mediterranean Sea. One hundred and twenty‐nine specimens ranging from 102 to 438 mm in total length (L_T) were used. Age estimations were based on the study of the otolith microstructure, which was revealed after grinding both frontal sides of otoliths. The enumerations of the daily growth increments (DGI) as well as their width (W_DGI) measurements were made on calibrated digital images. The number of DGI in otoliths ranged between 163 and 717. Four phases in the W_DGI evolution were distinguished: (1) larval–juvenile pelagic phase, with an increasing trend in W_DGI up to the 60th DGI, (2) settlement phase, with a short‐term deceleration in W_DGI between the 61st and 150th DGI, (3) juvenile demersal phase, characterized by a stabilization of W_DGI from 151st to 400th DGI and (4) adult phase, with a decreasing trend in W_DGI after the 400th DGI. Age, sex and month of formation were found to affect the W_DGI in all phases, with the exception of age at the juvenile demersal phase. The power curve with intercept model described best the relationship of M. merluccius L_T with age (T_DGI), according to Akaike criteria, revealing differences in growth between females [L_T = 65 · 36(T_DGI)^{0 · 40} ? 388 · 55] and males [L_T = 69 · 32(T_DGI)^{0 · 37} ? 352 · 88] for the sizes examined. The mean daily growth rates were 0·61 mm day^?1 for females and 0·52 mm day^?1 for males, resulting in an L_T of 283 and 265 mm at the end of their first year of life. In comparison with previous studies on the Mediterranean Sea, the results of this study showed a greater growth rate, similar to results from tagging experiments and otolith microstructure analyses for M. merluccius in other geographic areas.     

基于矢耳石形态特征的中国鲚属鱼类种类识别

分析了中国鲚属鱼类七丝鲚、凤鲚、刀鲚和短颌鲚共4种205尾2龄鱼矢耳石的32个形态特征。对9个可量性状的主成分分析表明,反映矢耳石体积和基叶大小的第1主成分,以及与反映翼叶大小的第2主成分共同解释了总变异的91.2%,是种类判别的主要依据。对10个比例性状的逐步判别显示,4个种的平均正判率达95.6%,但交互验证结果却显示,刀鲚与短颌鲚间存在着20.1%的误判率,表现出与传统的依据外部形态分类和线粒体DNA控制区全序列分析的相似结果。这表明,短颌鲚并非有效种,而是刀鲚的淡水生态型种群,也预示着耳石形态分析在近缘种判别方面的良好应用前景。     

Comparative study of growth of flatfishes on the west coast of Brittany

Lusitanian and boreal flatfish species live in the Bay of Douarnenez (Brittany, France); ten are abundant enough to be the subject of this growth investigation. In all species, females attain greater ultimate size than males, and oldest specimens are frequently female. Species are segre-gated to their longevity: those rapidly reaching their asymptotic length have the shortest life spans and also the highest values of the Von Bertalanffy parameter K .
In the bay, species of the boreal fish fauna (plaice, dab) find suitable environmental conditions for rapid growth; fish of the Lusitanian fauna (sand soles) grow slower than those living in southern areas.
In the Atlantic Ocean, the growth of the sole is better than in the North Sea and the Mediterranean.     

Lake Patzcuaro,Mexico: results of a new morphometric study and its implications for productivity assessments

Data for 25 morphometrical parameters describing the geomorphology of Lake Patzcuaro, Michoacan, Mexico have been derived from an up-to-date bathymeric map with contour-lines at 1.0 m intervals. Maximum depths were observed in the northern part of the lake whereas considerable shallow areas are developing in the south. Insulosity is continuously modified due to certain areas becoming part of the mainland and the appearance of new islands with increasing shallowness and man-made channels. The hydrographic survey was evaluated using the optimization model suggested by Hakanson (1978). An information value of 0.788 for 12 contour lines in the new bathymetric map is reported. The usefulness of accurate morphometrical data in process-orientated modelling for lake management is discussed.     

Mathematical modelling of primary production in Green Bay (Lake Michigan,USA), a phosphorus-and light-limited system

Application of mathematical models in the design and evaluation of lake restoration programmes must include due consideration of three basic concepts of model development; 1) that the model framework is appropriately matched to the intended management use, 2) that selection of the proper degree of model complexity is fundamental to the achievement of model credibility and 3) that field and laboratory studies must be designed and interpreted with the aid of the model to insure development of a comprehensive, integrated tool.These concepts are demonstrated for the case of lake restoration efforts in Green Bay (Lake Michigan, USA). Striking gradients in water quality (transparency, algal standing crop, hypolimnetic oxygen depletion) and trophic state occur along the major axis of the bay in response to phosphorus loaded from the Fox River. A simple model for gross primary production is developed to permit calculation of the relative importance of internal carbon production to the total organic carbon budget of the bay. Primary production varies from high rates over a limited photic depth in the turbid, phosphorus-rich waters of the eutrophic portions of the bay to low rates over an extensive photic depth in the transparent, phosphoruspoor reaches of the oligotrophic regions. Internal production accounts for approximately 90% of the total organic carbon loaded to the system over the summer growing season. Water quality management strategies must address the stimulation of primary production by phosphorus loaded from the Fox River in any attempt to lower the standing crop of nuisance algae, improve water clarity, and reduce rates of hypolimnetic oxygen depletion in Green Bay.     

An approach to modelling in immunology

Like most other fields in biology, immunology has been revolutionised by the techniques of molecular biology and the resulting explosion in available experimental data. It is argued that efforts to integrate the data to gain insight into how various subsystems in the immune system interact and function require mathematical modelling and computer simulation in close collaboration with experimentalists. This paper illustrates some of the techniques available for modelling immune systems, and highlights the issues that should be borne in mind by anyone starting down the modelling path.     

Interpretation of mixed sediment profiles by means of a sediment-mixing model and radioactive fallout

Chernobyl fallout provided a pulsed release to the environment and an opportunity to study sediment mixing processes in lakes. The paper presents the application of a mathematical modelling technique using a radionuclide as tracer. The model simulates the radionuclide profiles in sediments and computes the concentrations by solving numerically a one-dimensional mass-balance equation. The mixing-advection-decay model has been designed to include time-variable input capabilities and a depth-dependent mixing coefficient.     

The skin pattern of young plaice and its rapid modification in response to graded changes in background tint and pattern

Young plaice, kept on a standard background and trained for 3–4 weeks, were photographed to record short-term nervously controlled responses to plain grey and patterned backgrounds, graded and quantitatively defined with regard to reflectivity and dimensions. Systems of primary, secondary and lower-order black and white spots and flecks became prominent or hidden in hierarchical order. Spots at any one level in a hierarchy were approximately evenly distributed. Black spots enlarged with increased size or number of black circles in the background but responded differently to unpatterned grey backgrounds. White spots had a centre and surrounding annulus both of which could be pale or independently variably occluded centrally, peripherally or overall. Peripheral occlusion of the annuli contributed to skin darkening and by extending inwards to include the centre it progressively diminished the white spots. The system of white spots was responsible for the smaller skin patterns, the finest being produced through disruption by the white flecks of the annuli, black spots and dark patches. There was great variation in response of individuals. Erratic and poor background responses were generally associated with abnormalities in the white spots.     

Modelling seasonal variations in the age and incidence of Kawasaki disease to explore possible infectious aetiologies

The average age of infection is expected to vary during seasonal epidemics in a way that is predictable from the epidemiological features, such as the duration of infectiousness and the nature of population mixing. However, it is not known whether such changes can be detected and verified using routinely collected data. We examined the correlation between the weekly number and average age of cases using data on pre-vaccination measles and rotavirus. We show that age-incidence patterns can be observed and predicted for these childhood infections. Incorporating additional information about important features of the transmission dynamics improves the correspondence between model predictions and empirical data. We then explored whether knowledge of the age-incidence pattern can shed light on the epidemiological features of diseases of unknown aetiology, such as Kawasaki disease (KD). Our results indicate KD is unlikely to be triggered by a single acute immunizing infection, but is consistent with an infection of longer duration, a non-immunizing infection or co-infection with an acute agent and one with longer duration. Age-incidence patterns can lend insight into important epidemiological features of infections, providing information on transmission-relevant population mixing for known infections and clues about the aetiology of complex paediatric diseases.     

Modelling growth of brown trout, Salmo trutta, in terms of weight and energy units

1. The chief objectives were: (i) to compare two growth models, one based on weight and the other on energy, using the same data set for the analyses; (ii) to discover if weight and energy units can be simply interchanged for growth assessment. The data set was for 183 brown trout, Salmo trutta (live weight 1–300 g), fed to satiation on shrimps, Gammarus pulex, and grown individually over 42 days at constant temperatures (range 3.8–20.4 °C). 2. Rates of change in weight or energy content, and final weight or energy content at the end of 42 days growth, were estimated from the models and were excellent fits to the experimental data (P < 0.001). The shape of the temperature relationship for rates of change or final values was triangular for the weight model and curvilinear for the energetics model. Optimum temperatures for growth according to the weight and energetics models were 13.1 and 13.9 °C, respectively, for rates of change and 13.1 and 13.5 °C, respectively, for final values. When the growth period was extended to 100 and then 300 days, the triangular relationship and optimum temperature remained the same for the weight model, but the curvilinear relationship became more triangular for the energetics model and the optimum temperature identical to that in the weight model. The relationship between gross efficiency and temperature also differed in shape between the two models but maximum efficiencies occurred at a similar value of 9 ± 0.1 °C (18 and 32% for weight and energetics models). As fish weight increased, gross efficiency remained constant in terms of energy units, but decreased markedly in terms of weight. 3. These comparisons showed that different conclusions can be drawn from the two models, even if the same data set was analysed. There was a close relationship between initial wet weight and energy content for stock trout used in the experiments, but the relationship was not so close at the end of the experiments, and interchangeability of units could no longer be assumed. A variable error, often as high as 10–12%, would occur if the relationship for initial values was used to predict one unit from the other. Therefore, weight and energy units cannot be simply interchanged for growth assessment, especially in comparisons for trout of different sizes.     

Mathematical Modelling of Lipase Catalysed Resolution of O-Acetyl and O-Formyl Derivatives of Secondary Alcohols

Lipase catalysed transesterification of O-acetyl and O-formyl derivatives of several sterically hindered secondary alcohols with n-butanol is studied. The reaction is mathematically modelled and the rate constants in the model are evaluated by transient parameter estimation procedure. Several models are considered for predicting the enantiomeric excess (ee) of the product and compared with experimental observations. It is found that the maximum ee depends only on the rate constants of the two competing reactions and not on the order of reaction. A second order model is found to predict the observed behaviour well. When the data is fitted to an equilibrium type of model developed by Chen et al. (1987), it is found that the rate of forward reaction is several orders of magnitude larger than the rate of reverse reaction. The effect of acetyl and formyl groups on the reactivity and selectivity are also discussed.     

ADMET: ADipocyte METabolism mathematical model

White fat cells have an important physiological role in maintaining triglyceride and free fatty acid levels due to their fundamental storage property, as well as determining insulin resistance. ADipocyte METabolism is a mathematical model that mimics the main metabolic pathways of human white fat cell, connecting inputs (composition of culture medium) to outputs (glycerol and free fatty acid release). It is based on a set of nonlinear differential equations, implemented in Simulink® and controlled by cellular energetic state. The validation of this model is based on a comparison between the simulation results and a set of experimental data collected from the literature.     

HEMETβ: improvement of hepatocyte metabolism mathematical model

This article describes hepatocyte metabolism mathematical model (HEMETβ), which is an improved version of HEMET, an effective and versatile virtual cell model based on hepatic cell metabolism. HEMET is based on a set of non-linear differential equations, implemented in Simulink®, which describes the biochemical reactions and energetic cell state, and completely mimics the principal metabolic pathways in hepatic cells. The cell energy function and modular structure are the core of this model. HEMETβ as HEMET model describes hepatic cellular metabolism in standard conditions (cell culture in a plastic multi-well placed in an incubator at 37°C with 5% of CO₂) and with excess substrates concentration. The main improvements in HEMETβ are the introductions of Michaelis–Menten models for reversible reactions and enzymatic inhibition. In addition, we eliminated hard non-linearities and modelled cell proliferation and every single aminoacid degradation pathway. All these innovations, combined with a user-friendly aspect, allow researchers to create new cell types and validate new experimental protocols just varying ‘peripheral’ pathways or model inputs.     

The effect of sand and light on predation of juvenile plaice (Pleuronectes platessa) by fishes and crustaceans

Rates of predation on 0-group plaice, Pleuronectes platessa . in aquaria were compared under four different combinations of conditions to test the hypothesis that the presence of sand in which they may bury affords a refuge from predators. The effect of light and darkness on predation rate was also examined, Two crustaceans, the shrimp, Crangon crangon , and the portunid crab, Liocarcinus holatus , and two fishes, cod, Gadus morhua , and pollack, Pollachius pollachius , were used as predators. Predaton rates were significantly higher in the dark for all predators except pollack. Predation rates in the absence of sand were signifcantly greater only for pollack. The results suggest that predation rates on plaice during their juvenile nursery stage on sandy beaches will be significantly greater during darkness than during the day. Burying in sand appears to provide only a partial refuge from predation, perhaps because natural predators have evolved effective methods of foraging for buried prey.