Fish Mass Research Articles

Effects of body mass and water temperature on routine metabolism of American paddlefish Polyodon spathula

This study quantified the effects of temperature and fish mass on routine metabolism of the American paddlefish Polyodon spathula. Thermal sensitivity, as measured by Q(10) value, was low in P. spathula. Mean Q(10) was 1·78 while poikilotherms are generally expected to have Q(10) values in the 2·00-2·50 range. Mass-specific metabolism did not decrease with increased fish size to the extent that this phenomenon is observed in teleosts, as evidenced by a mass exponent (β) value of 0·92 for P. spathula compared with 0·79 in a review of teleost species. Other Acipenseriformes have exhibited relatively high β values for mass-specific respiration. Overall P. spathula metabolism appears to be more dependent on body mass and less dependent on temperature than for many other fishes. An equation utilizing temperature and fish mass to estimate gross respiration for P. spathula was derived and this equation was applied to respiratory data from other Acipenseriformes to assess inter-species variation. Polyodon spathula respiration rates across water temperature and fish mass appear most similar to those of Atlantic sturgeon Acipenser naccarii and white sturgeon Acipenser transmontanus.

Within‐lake distribution patterns of fish assemblages: the relative roles of spatial, temporal and random environmental factors in assessing fish assemblages using gillnets in a large and shallow temperate lake

In this study, the relative role of spatio-temporal factors and associated environmental variables (water transparency and temperature) were quantified in relation to gillnet samples of fishes in a large and shallow lake (Lake Balaton, Hungary). Most of the variance (56·1%) in the relative abundance data (%) was related to the vertical segregation of fishes. This gradient substantially affected the catch per unit effort (CPUE) by number of the dominant species, the surface-oriented bleak Alburnus alburnus and the benthic common bream Abramis brama. It also influenced total CPUE, mean fish mass and species richness and diversity. At the lake level, horizontal habitat heterogeneity (i.e. littoral v. offshore) accounted for only 8·3% of the total variance in relative abundance data, but was important in structuring the CPUE of the ruffe Gymnocephalus cernua and the pikeperch Sander lucioperca. The longitudinal environmental gradient (i.e. lake basin), year and season of sampling, water transparency and temperature had significant effects on relative abundance only at the habitat level, but were also important components of variability of CPUE in some species at the lake level. As sampling schemes need to consider the main gradients in fish assemblage distributions, the use of surface and pelagic gillnets should be more intensively incorporated in the study and monitoring of fish assemblages in shallow lakes and lake habitats.

Ontogenetic shifts in morphology and resource use of cisco Coregonus artedi

Two previously described lacustrine cisco Coregonus spp. morphs [i.e. a small (<300 mm fork length, L(F)), low-gillraker (≤44) morph and a large (≥300 mm L(F) ), high-gillraker (≥45) morph] from Great Slave Lake, NT, Canada, were found to be synonymous with cisco Coregonus artedi. Geometric body shape did not differ between the two size classes nor could they be differentiated by 24 size-corrected linear measurements, indicating that the two groups had similar phenotypes. Strong, positive correlations between all linear characters and geometric centroid size (a composite variable of fish body length, mass and age) suggested that body morphology changed with age as fish grew. Total gillraker number (N(GR)) increased with L(F) according to: N(GR) = 36.3 + 0.034L(F). Differences in gillraker number and phenotype with age and size were explained by shifts in habitat and trophic resource use. Relative abundance within 0-30, 30-60, 60-90 and >90 m depth strata differed between size classes suggesting that morphology changed when fish shifted their habitat as they grew older. Large C. artedi had lower δ(13)C and slightly higher δ(15)N, indicating greater reliance on pelagic prey resources (i.e. more or larger zooplankton, such as Mysis spp.), compared to small C. artedi, which relied slightly more on benthic prey. Gillraker shape and number have always been used as key diagnostic characters in coregonine taxonomy; based on the findings presented here, ontogenetic shifts should be accounted for in resulting classifications.

The influence of nutrition on rainbow trout (Oncorhynchus mykiss) meat quality

Feed of high quality is one of the most important parameter which influences fish growth, feed conversion and chemical composition of fish meat in conditions of intensive fish farming. Studies on the influence of two commercial diets on nutritional quality and production results in rainbow trout intensive farming conditions in Pond I and Pond II were undertaken. Obtained values for proteins and fats in feed were significantly higher (p&lt;0.001) in Diet II comparing to Diet I. The average water and ash content was significantly higher (p&lt;0.001) in Diet I in relation to Diet II. The average length and mass of fish were higher in Pond I in relation to Pond II. Calculated values for condition factors, Kf, indicate to a higher production results in Pond II (1.81) in relation to Pond I (1.22). There were not significant differences (p&gt;0.05) in the average content of proteins and ash in fillets of fish from Pond I (17.43% and 1.19%, respectively) and Pond II (18.69% and 1.29%, respectively). The average content of water was significantly higher (p&lt;0.001) in fillets of fish from Pond I (79.87%) comparing to fillets of fish from Pond II (75.40%). Average content of fat in fillets of trout from Pond II (4.17%) was around three times higher than the average content of fat in fillets of trout from Pond I (1.41%), (p&lt;0.001). Results for energy values (348.44 kJ/100g- Pond I and 471.38 kJ/100g- Pond II) are in a direct correlation with the content of fat in fish. The average content of cholesterol in fillets of trout from Pond II (70.12 mg/100g) was significantly higher (p&lt;0.001) than in fillets of trout from Pond I (44.11 mg/100g). The obtained data indicate to a positive influence of fat content in the diet on fat content, energy value and production results in rainbow trout production in Pond II. Lower water temperature established in Pond II (8?C) comparing to Pond I (13?C) might have had additional influence on the nutritional quality and production results in Pond II, as well.

The effects of rearing density on growth, size heterogeneity and inter-individual variation of feed intake in monosex male Nile tilapia Oreochromis niloticus L.

The growth dispersion of farmed fish is a subject of increasing interest and one of the most important factors in stocking density. On a duration of 60 days, the effect of stocking density on the growth, coefficient of variation and inter-individual variation of feed intake (CVFI) of juvenile Nile tilapia Oreochromis niloticus L. (14.9 ± 1.2 g) were studied in an experimental tank-based flow-through system. Groups of fish were stocked at four stocking densities: 200, 400, 600 and 800 fish/m3, corresponding to a density of ∼3, 6, 9 and 12 kg/m3 and referred to as D1, D2, D3 and D4, respectively. Each treatment was applied to triplicate groups in a completely randomized design. No treatment-related mortality was observed. The fish densities increased throughout the experiment from 3 to 23.5, 6 to 43.6, 9 to 56.6 and 12 to 69 kg/m3. Results show that mass gain and specific growth rate (SGR, %M/day) were negatively correlated with increased stocking density. Groups of the D1 treatment reached a mean final body mass (FBM) of 119.3 g v. 88.9 g for the D4 groups. Feed conversion ratios (FCRs) were 1.38, 1.54, 1.62 and 1.91 at D1, D2, D3 and D4 treatments, respectively. Growth heterogeneity, expressed by the inter-individual variations of fish mass (CVM), was significantly affected by time (P < 0.001), stocking density (P < 0.001) and their interaction (P < 0.05). The difference in CVM was particularly conspicuous towards the end of the experiment and was positively correlated with stocking density. Similarly, radiographic study shows that CVFI was also found to be significantly greater for groups reared at high stocking densities (D3 and D4) than the other treatments (D1 and D2). These differences in both CVM and CVFI related to the stocking density need to be taken into account by husbandry practices to assure the production of more homogeneous fish size. A simple economic analysis indicates a parabolic relationship between profit and density with optimal final density at the peak of the curve. Given reasonable assumptions about production costs, the optimal final density (Dopt) is 73.7 kg/m3. A sensitivity analysis shows that changes in the fixed cost have no effects on the optimal final density. However, small change in variable costs, such as feed and juvenile costs, may have substantial effect on the optimal density.

CLIMBING GOBIES HAVE SMALL BUT POWERFUL SUCKERS

Scaling waterfalls through torrents of water would be an impressive feat for any creature, but for tiny juvenile gobies returning to their homes in the upper reaches of island streams, it's an inevitable rite of passage. Many goby larvae are washed out to sea soon after hatching, so species that reside in the upper reaches of streams have no choice but to scale obstacles in their path on the return journey. However, the youngsters are well prepared for this trial. They have a sucker formed from fused pelvic fins on their undersides that they use for climbing. Adult fish also face the risk of being washed downstream. However, they seem to climb less than youngsters. According to Takashi Maie from Clemson University, USA, the adults' suckers may not adhere strongly enough to support the larger fish's mass, as their suckers only increase in size in proportion to their body length, whereas their mass increases much more. Intrigued by this possibility, Maie realised that he would have to measure the adhesive pressure and sucker suction force from fish with different lifestyles and of different sizes to find out how their adhesion varies as they grow. Teaming up with Heiko Schoenfuss from St Cloud State University, USA, and Richard Blob from Clemson, Maie travelled to the Hilo field station of the Division of Aquatic Resources, Hawai‘i, to measure how tightly goby suckers fasten to surfaces (p. 3925).Scrambling up waterfalls to the gobies' homes and donning wetsuits to snorkel and catch the fish, the trio successfully collected five species of climbing fish ranging in size from 0.1 to 15 g, in addition to one non-climbing species collected at low altitude. Back at the field station, the team gently anaesthetised the fish and lightly touched their suckers to a simulated climbing surface. The suckers immediately formed a seal and stuck on. Measuring the pressure in the cavity between the sucker and surface at inclinations ranging from 45 deg to over 90 deg and comparing the sucker sizes and adhesive forces between the two lifestyles (climbing and non-climbing), Maie and his colleagues noticed that the non-climbers' suckers increased in size much more rapidly than if they were growing in proportion to the rest of the body, whereas the climbers' suckers only grew in proportion of the rest of their bodies. The non-climbers' suckers were relatively large for their size.Next the team measured the sucker's adhesion as the fish ascended waterfalls. After building a gently cascading simulated miniwaterfall, Maie drilled a hole in the surface, inserted a pressure transducer to measure the fish's adhesion and waited for the animals to pass over the pressure transducer as they ascended the slope. Comparing the climbers' suction force with the passive force that they had measured when the fish were anaesthetised, Maie realised that the active suction forces were more than twice as great as the passive, and were sufficient to bear more than twice the fish's mass. In contrast, the non-climbers' adhesion forces were much weaker than those of their climbing cousins, despite the relatively large size of their suckers. The team suspects that the non-climbers enlarged suckers may compensate for their weaker adhesion.Having shown that climbing gobies have smaller suckers than their non-climbing cousins but that the climbers' suction is much stronger, Maie explains that the climbers actively expand their suckers while in contact with the surface to increase their suction, and he and his colleagues are keen to find out how the muscles and ray structures that support the sucker alter with age to help growing gobies get a grip.

Field assessment of the mid winter mass kills of trophic fishes at Mariotteya stream, Egypt: Chemical and biological pollution synergistic model

Pathogenic Candida albicans was isolated from water and fish samples collected during an emergent event of mass mortalities among the juvenile Nile tilapia (Oreochromis niloticus), Sharp toothed catfish (Clarias gariepinus) along the stream of Mariotteya drainage. Investigations indicated that fish mortalities were confined to the area of Shubramant and Aboul Noumros (North to Sakara 7 drainage). C. albicans was isolated from the lesions associated with multiple skin ulcers in both Nile tilapia juveniles and Sharp toothed catfish. Assessment of the field and laboratory data has indicated that Mariotteya environmental disaster was a multifactorial problem. The fish mass kills were initially flared up through the dumping of the improperly treated nasty organic and inorganic chemicals from Elhawamdia sugar factory and municipal sewage. The physical stagnation of the stream, high levels of ammonia, phenol and polycyclic aromatic hydrocarbons (PAHs) and low levels of dissolved oxygen (DO) were all incriminated as the initial stimulus behind biological invasion of pathogenic bacteria (Pseudomonas fluorescence) and yeast (C. albicans). Pathologically, fishes were dying from both respiratory and osmoregulatory failure induced by the severe damage of both gills and skin. It has been implied that such environmental pollutants have direct damaging effects on gills, skin and fins with consequent suppression of the skin’s natural innate components. The adversely confronted immunological barriers were further exacerbated by the possible synergistic interactions of P. fluorescence dermotropic toxins followed by the secondary invasion of the pathogenic C. albicans.

SUITABILITY INDEX FOR COASTAL ENVIRONMENT RESTORATION IN ENCLOSED BAY

HSI (Habitat Suitability Index) models are a numerical index that describes the habitat quality for individual species of aquatic organism. This models are composed of SI (suitability index) models, which show the cause-and-effect relationships between biomass of target species and the variation of individual water environmental factors. Fish are often used as the environmental indicator species of HSI models, because fish are strongly related to marine algae, sea grass, water quality, and so forth, and fish are predator high in the food chain for the aquatic system. &#x0D; In order to restore the marine environment of Tokyo Bay, in Japan(Fig.1), some SI models have been proposed. However, we have few precision SI models on target fish. Therefore, the objective of this study is to reveal the relationship between seasonal or daily variations of water environment components in Tokyo bay or in offshore sea area of the Pacific coast of Tokyo metro (Fig.1) and the total mass of fish living in Tokyo bay in order to create precision SI models of fish.

Intra‐ and interspecific differences in nutrient recycling by European freshwater fish

Summary1. We measured N and P excretion rates of 470 individuals belonging to 18 freshwater fish species widespread in Western Europe. We assessed the effect of body mass on excretion rates at both the intra‐ and interspecific levels.2. The high variability in per capita N and P excretion rates was mainly determined by differences in body mass. The scaling coefficients of allometric relationships for both N and P excretion rates were significantly lower than 1 (mean ± SE, 0.95 ± 0.04 and 0.81 ± 0.05, respectively).3. The slope of the allometric relationship between fish mass and nutrient excretion rate was significantly different among species. We did not detect any influence of phylogenetic conservatism on fish mass and on excretion rates. Further investigations are needed to understand the biological determinants of these differences.4. This high intra‐ and interspecific variability in per capita excretion rates, coupled with differences in fish body mass, produce marked differences in biomass‐standardised excretion rates. These results thus indicate the necessity for further experimental and in situ investigations on the consequences of nutrient recycling by fish in freshwater ecosystems.

Annual Variation in the Diet of Breeding European Shag (Phalacrocorax Aristotelis) in Central Norway

Abstract. The diet of breeding European Shag (Phalacrocamx aristotelis) was studied at Sklinna, one of the world's largest colonies, during 2007–2010. Regurgitated pellets were collected regularly throughout the chick rearing period and hard parts used to identify prey items to the lowest possible taxonomic level. The length and width of otoliths were used to estimate fish body length and mass. Shags' diet was varied and contained at least 17 different species of fish. Gadoid species, including saithe (Pollachius virens), cod (Gadus morhua) and Poor Cod (Trisopterus minutus), were the main prey and contributed approximately 90% of the diet during the study period. Saithe dominated the diet by numerical frequency, biomass and frequency of occurrence in all study years. Sandeels (Ammodytidae) contributed little to shag diet. The numerical frequency and percentage saithe biomass was lower in 2010 than in the other years. However, this was compensated by a higher frequency of cod and poor cod, making the tota...

Mercury Concentrations in Muscle and Liver Tissue of Fish from Marshes Along the Magdalena River, Colombia

The present research determined the total mercury concentrations in muscle and liver tissue in fish collected from the Magdalena River watershed. A total of 378 muscle samples and 102 liver samples were included in the analysis. The highest mean mercury level in muscle tissue was found in the noncarnivore, Pimelodus blochii. However, as a group, carnivores had significantly higher (p < 0.05) mercury levels in their muscle tissue than noncarnivores. A significant correlation (p < 0.05) was obtained between fish mass and mercury concentrations in muscle or liver in four species. No differences were observed in total mercury concentration based either on species or gender.

Fish pollution with anthropogenic 137Cs in the southern Baltic Sea

This paper presents the results of a study on changes in 137Cs activity concentrations in three fish species from the southern Baltic Sea: cod (Gadus morhua), herring (Clupea harengus) and flounder (Platichtys flesus), in the period 2000–2010. During the study period a marked decline in cesium activity concentration in fish muscle tissue was observed, which reflected changes in radionuclide activity concentration in seawater. No statistically significant temporal trends were determined in changes of concentration factors (CFfish/seawater) calculated for the examined fish species. The analysis of 137Cs activity as a function of ichthyological parameters revealed the lack of a relationship between radionuclide activity concentrations in herring muscle tissue and the fish age in an narrow age range (2–4years). However, a reverse proportionality of total fish mass, as well as body length, against 137Cs activity concentrations in muscles was well documented. The latter observation can be the direct result of the dilution effect related to the increase of fish body weight. 137Cs activity concentration in muscle tissue of the five fish species forms a declining sequence: Gadus morhua, Platichthys flesus, Clupea harengus, Perca fluviatilis and Neogobius melanostomus.

DESIGN AND EVALUATION OF A PNEUMATIC FISH FEED DISTRIBUTOR FOR EGYPTIAN FISH FARMS

A pneumatic fish feed distributor was designed and locally fabricated for Egyptian fish farms to ensure all the fish have equal access to the feed and avoid the manual feeding problems. The performance of the designed pneumatic fish feed distributor was evaluated based on fish pellet degradation, uniformity of fish feed distribution pattern and performance of feeding method. The evaluation was calculated at different operation conditions including different blower air speeds from 10 to 20 m/s, forward speed from 2.62 to 6.39 km/h (from 0.73 to 1.78 m/s, respectively) and feed rates from 10 to 25 kg/min. The obtained results lead to the conclusion that: Using of pneumatic fish feed distributor gave the best results of feed distribution pattern uniformity, eliminated feed breakage wasted as dust and saved about 35%, in fish feeding cost under the optimum operating conditions of air blower speed of 15 m/s, forward speed ranging from 2.53 to 3.42 km/h and feed rate ranging from 20 to 25 kg/min. Using mechanical feeding method (pneumatic fish feed distributor) gained 208.18 ± 24.25 g as an average fish mass with coefficient of variation (C.V) about 11.47% and better feed conversion ratio (FCR) of 1.63 comparing with 183.46 ± 42.73g fish mass with C.V about 23.29% and poor FCR of 1.94 gained by using the hand feeding method at the end of production cycle. Using of pneumatic fish feed distributor is more suitable and acceptable mechanical feeding method to ensure that all the fish have equal access and similar opportunity to the feed which achieving higher uniformity in growth rate and good feed conversion ratio. In addition, it helps avoiding the manual feeding problems of water pollution due to eliminating waste of pellets dissolved in the water and reduces the feeding labor and cost. Consequently, it increases the benefit margins of fish farm production. Therefore, it is recommended to use pneumatic fish feed distributor under the previous optimum operating conditions.

Fish mass mortalities are not always related to environment

Fish mass mortalities are not always related to environment

Comparing Multiple Predictors of Energy Content in Juvenile Bluefish

AbstractThe need to estimate energetic status in fish is common, but determining energy content is costly. We examined the relationship between the energy density of wild juvenile bluefish Pomatomus saltatrix (115–310 mm) and multiple indicators of energetic status to develop regression models for predicting bluefish energy content. Energy density was strongly related to the percent dry mass of whole fish (r2 = 0.99) but poorly related to residual wet mass (r2 = 0.33), a commonly used condition index. Energy density was related to three hepatosomatic indices: liver wet mass (r2 = 0.45), liver dry mass (r2 = 0.64), and liver energy content (r2 = 0.70). Energy density was nonlinearly related to percent dry weight in muscle tissue (r2 = 0.93) and energy density in muscle tissue (r2 = 0.83). A biphasic pattern of lipid storage was found in muscle tissue, with very little lipid stored until after a threshold in percent dry weight is exceeded. Using our predictive equation, the energy content in whole bluefish can be determined using the percent dry weight of muscle tissue. However, our predictive model should only be used for wild‐caught bluefish because laboratory‐held fish exhibited higher lipid : protein ratios in muscle tissue.

Impact of a telemetry-transmitter implant on daily behavioral rhythms and physiological stress indicators in gilthead seabream (Sparus aurata)

The effect of intracoelomic tagging of an acoustic telemetry transmitter (1.65% ratio of tag mass in the air to fish mass in the air) on behavioral (food intake and locomotor activity) and physiological (blood glucose and plasma cortisol) parameters of gilthead seabream was investigated. To this end, fish (289 ± 53 g, mean ± SD) were divided into 3 experimental groups: control (C), transmitter (T, inserted surgically) and sham group (S, subjected to surgery but without transmitter insertion). Blood was extracted during surgery and 9 days later. Throughout the trial, fish were fed by means of self-feeders and locomotor activity was measured by means of an infrared photocell. Two days after the first manipulation, a significant decrease in food intake could be observed in all the experimental groups. The fact that food intake was not affected after the second manipulation seems to indicate that a learning process took place for handling. The rhythmicity of feeding and locomotor activity was not affected by handling in any experimental group. However, group T showed increased plasma cortisol levels 9 days after surgery. In conclusion, while most behavioral parameters were not affected by handling, the plasma cortisol levels of seabream 9 days after insertion of the transmitter indicated a physiological impact that should be taken into account in long-term radiotracking studies, since such an operation could have negative effects on wild individuals after the end of the tracking experiments.

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature-controlled, Brett-type swimming-tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L(F) ), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U(crit)) was 102·5 ± 13·7 cm s⁻¹ or 4·6 ± 0·9 L(F) s⁻¹. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U(max,c)) was 99·4 ± 14·4 cm s⁻¹ or 4·5 ± 0·9 L(F) s⁻¹. Oxygen consumption rate (M in mg O₂ min⁻¹) increased with swimming speed and with fish mass, but mass-specific M (mg O₂ kg⁻¹ h⁻¹) as a function of relative speed (L(F) s⁻¹) did not vary significantly with fish size. Mean standard metabolic rate (R(S) ) was 170 ± 38 mg O₂ kg⁻¹ h⁻¹, and the mean ratio of M at U(max,c) to R(S) , an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U(opt) ), at which the gross cost of transport was a minimum of 2·14 J kg⁻¹ m⁻¹, was 3·8 L(F) s⁻¹. In a subset of the fish studied (19·7-22·7 cm L(F) , 106-164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L(F) . The mean propulsive wavelength was 86·7 ± 5·6 %L(F) or 73·7 ± 5·2 %L(T) . Mean ±s.d. yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L(F) ; 23·4, 25·3 and 26·4 cm L(T) ), were 4·6 ± 0·1 and 17·1 ± 2·2 %L(T) , respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.

Force estimation and prediction from time-varying density images

We present methods for estimating forces which drive motion observed in density image sequences. Using these forces, we also present methods for predicting velocity and density evolution. To do this, we formulate and apply a Minimum Energy Flow (MEF) method which is capable of estimating both incompressible and compressible flows from time-varying density images. Both the MEF and force-estimation techniques are applied to experimentally obtained density images, spanning spatial scales from micrometers to several kilometers. Using density image sequences describing cell splitting, for example, we show that cell division is driven by gradients in apparent pressure within a cell. Using density image sequences of fish shoals, we also quantify 1) intershoal dynamics such as coalescence of fish groups over tens of kilometers, 2) fish mass flow between different parts of a large shoal, and 3) the stresses acting on large fish shoals. IEEE Transactions on Pattern Analysis and Machine Intelligence 33(6), pp. 1132-1146 (2011)

Why mercury concentration increases with fish size? Biokinetic explanation

In field-collected juvenile blackhead seabream Acanthopagrus schlegeli schlegeli, measured total mercury (THg) and methylmercury (MeHg) concentrations were related to 0.19 and 0.33 power of fish mass over a wide size range (more than 50-fold). The causative factors remain unclear. In this study, size-dependent biokinetic parameters for both inorganic mercury [Hg(II)] and MeHg were estimated, and their relative contributions to size-related Hg accumulation were further assessed. Except for the MeHg dietary assimilation efficiency (AE), which was not affected by the fish size, other examined biokinetic parameters showed either positive (Hg(II) AE) or negative correlations (growth rate constant-g, dissolved uptake rate constant-ku and efflux rate constant-ke) with fish size. The biokinetic variation explained the observed allometric pattern of Hg accumulation in juveniles. Especially, both size-related g and ke were the key drivers. The current study addressed the importance of size-related biokinetics, in particular the ke and g, which have important implications to manage Hg contamination in fisheries.

Von Bertalanffy's growth dynamics with strong Allee effect

Von Bertalanffy’s model is one of the most popular differential equation used in order to study the increase in average length or weight of fish. However, this model does not include demographic Allee effect. This phenomenon is known in the fisheries literature as “depensation”, which arises when populations decline rapidly at low densities. In this paper we develop and investigate new corrected von Bertalanffy’s models with Allee effects. The generalization that we propose results from considering correction factors, one of rational type and the others of polynomial type, where two parameters are considered. The use of a parameter C > 0 leads the presented generalization, which yields some more flexible models with variable extinction rates. An Allee limit or unstable equilibrium Eu is incorporated so that the models under study have strong Allee effect. We analyze and show the transition from the strong Allee effect to the inexistence of this effect, through by a “weakening” of the Allee effect, depending on the parameters C and Eu. Finally, we discuss the flexibility of corrected von Bertalanffy’s sigmoid growth curves. So, the correspondents inflexion points are variable, i.e., the fish mass when the growth rate is maximum may be varied.