Optimal Harvesting Time in Aquaculture Assuming Nonlinear Size-Heterogeneous Growth

This study explores the optimal harvesting time in a size-heterogeneous population dynamics. The model includes the effect of population density in both the mortality rate and individual growth. An application to specific conditions of shrimp culture in Mexico is presented. The optimal harvesting rule is numerically found for different economic and productive scenarios. Parallel results are also obtained under the hypothesis of homogeneous population growth, which has been traditionally considered in the economic literature. In general, the discounted net revenue of the firm is underestimated if the size-heterogeneity phenomenon is not taken into account, while the calculated harvesting time shortens the predictions based on the homogeneous growth hypothesis. These results reveal that optimal management rules are significantly mistaken if the size-heterogeneity phenomenon is not taken into account.Keywords: Aquaculture, Aquaculture Efficiency and Management, Fisheries Economic

Environmental Determinants of COVID 19 Transmission Across a Wide Climatic Gradient in Chile

Several studies have examined the transmission dynamics of the novel COVID-19 disease in different parts of the world. Some have reported relationships with various environmental variables, suggesting that spread of the disease is enhanced in colder and drier climates. However, evidence is still scarce and mostly limited to a few countries, particularly from Asia. We examined the potential role of multiple environmental variables in COVID-19 infection rate [measured as mean relative infection rate = (number of infected inhabitants per week / total population) × 100.000) from February 23 to August 16, 2020 across 360 cities of Chile. Chile has a large climatic gradient (≈ 40º of latitude, ≈ 4000 m of altitude and 5 climatic zones, from desert to tundra), but all cities share their social behaviour patterns and regulations. Our results indicated that COVID-19 transmission in Chile was mostly related to three main climatic factors (minimum temperature, atmospheric pressure and relative humidity). Transmission was greater in colder and drier cities and when atmospheric pressure was lower. The results of this study support some previous findings about the main climatic determinants of COVID-19 transmission, which may be useful for decision-making and management of the disease.Funding was provided by the Initiation Fondecyt project 11170390 to F.C.A. D.N. received a CONICYT-PFCHA/ Doctorado Nacional/2019-21191862 scholarship. A.C. received a scholarship of the National Secretariat of Science, Technology and Innovation (SENACYT, Panama) and by the National Research System of Panama (SNI; doctoral student category)

Determination of the respiratory compensation point by detecting changes in intercostal muscles oxygenation by using near-infrared spectroscopy

This study aimed to evaluate if the changes in oxygen saturation levels at intercostal muscles (SmO2-m.intercostales) assessed by near-infrared spectroscopy (NIRS) using a wearable device could determine the respiratory compensation point (RCP) during exercise. Fifteen healthy competitive triathletes (8 male; 29±6 years; height 167.6±25.6 cm; weight 69.2±9.4 kg; V ̇O2-máx 58.4±8.1 mL·kg-1·min-1) were evaluated in a cycle ergometer during the maximal oxygen-uptake test (V ̇O2-máx), while lung ventilation (V ̇E), power output (watts, W) and SmO2-m.intercostales were measured. RCP was determined by visual method (RCPvisual: changes at ventilatory equivalents (V ̇E·V ̇CO2-1, V ̇E·V ̇O2-1) and end-tidal respiratory pressure (PetO2, PetCO2) and NIRS method (RCPNIRS: breakpoint of fall in SmO2-m.intercostales). During exercise, SmO2-m.intercostales decreased continuously showing a higher decrease when V ̇E increased abruptly. A good agreement between methods used to determine RCP was found (visual vs NIRS) at %V ̇O2-máx, V ̇O2, V ̇E, and W (Bland-Altman test). Correlations were found to each parameters analyzed (r=0.854; r=0.865; r=0.981; and r=0,968; respectively. p<0.001 in all variables, Pearson test), with no differences (p<0.001 in all variables, t-student test) between methods used (RCPvisual and RCPNIRS). We concluded that changes at SmO2-m.intercostales measured by NIRS could adequately determine RCP in triathletes

Opportunities for strengthening aquaculture industry through multicriteria decision-making

In operations research, there are methodological tools included in decision theory that can help decision-makers understand and systematize the decision-making process. Decisions can be classified either as mono-criterial, when only one criterion or goal is considered to evaluate its performance or multicriterial, which takes into account the interaction between two or more goals or criteria that can be in conflict. Natural resource management and finance are some important examples where the implementation of this type of tools has benefited the decision- making process because they allow a number of criteria or objectives to be weighted in a transparent manner to assist when one or more decision-makers are involved. Despite this, its application was not common in aquaculture; however, in recent years, efforts have increased exponentially. This work seeks to identify opportunity areas for development of new aquaculture-related research through the implementation of multicriterial decision-making methods (MCDM). To achieve this, a comprehensive bibliometric analysis was performed to detect MCDM applications that have been implemented in aquaculture industry (24 documents that were grouped into eight applications). Later, this information was complemented through the analysis of selected applications in natural resources management, specifically in fisheries, animal husbandry and agriculture. We propose 23 research topics relevant to the aquaculture industry that can be addressed by the methodologies in MCDM

Optimal harvesting time of farmed aquatic populations with nonlinear size-heterogeneous growth

This paper examines the question of optimal harvesting time in a size‐heterogeneous farmed aquatic population, using a model reflecting the effect of population density on both overall mortality rate and individual growth. This analysis enables an optimal harvesting rule to be deduced. The results obtained are applied to shrimp culture in recirculation systems in Mexico. Numerical solutions are derived for different production scenarios. Assuming identical culture conditions, results are also obtained under the hypothesis of homogeneous population growth, the view traditionally taken in the relevant economic literature. The optimal harvesting times calculated tend to decrease with higher densities, although this rule fails under the size‐heterogeneous population model. In general, optimal harvesting times are overestimated when size‐homogeneity in the culture is assumed. Our analysis reveals that management predictions are significantly mistaken if the size‐heterogeneity phenomenon is not taken into account.5134770,3140,556Q3Q4SCI

Growth modelling including size heterogeneity: Application to the intensive culture of white shrimp (P. vannamei) in freshwater

This article models the growth of a population in aquaculture, including the phenomenon of size heterogeneity. Experimental observations of six initial densities (90, 130, 180, 230, 280 and 330 shrimps m(-2)) in an intensive culture of Penaeus vannamei in freshwater were used to fit a growth model. For this, three mathematical functions were analysed (Gompertz, von Bertalanffy and Putter), which were modified in order to include the effect of initial density. Two models were constructed, one assuming the hypothesis of homogeneous individual growth and the other including size-heterogeneity throughout the culture cycle. For the second case, a stabilisation time was evaluated which defines the future heterogeneity of the cohort. In each initial density, the stabilisation phase was reached at approximately 2 g. However, the time taken for this phase to start increased with increasing initial culture density. The modified von Bertalannfy function was the most effective of the three equations in predicting growth. The weight predictions, assuming homogeneity and variability of sizes, presented low Percentage Root Mean Square Errors (PRMSE). However, the inclusion of size variability in the fit produced better statistical results than when they were not included (PRMSE decreased from 16% to 12%). This confirms the importance of taking into account size heterogeneity at an intensive level. Particularly at the technical level when the aquaculture producer is required to make stocking and harvest plans. (C) 2013 Elsevier B.V. All rights reserved.1210,6661,232Q2Q2SCI

Diferencias en los niveles de homofobia y transfobia entre estudiantes de educación física y otras pedagogías de Chile

Homophobia and transphobia are feelings of rejection and hostility towards homosexual and transgender people, which arise from prejudices and fears towards sexual diversity. The objective of the present research was to compare the homophobia and transphobia levels of physical education students and other pedagogies in Chile. To this end, the homophobia scale EHF-10 and the negative attitudes to trans people scale were applied to 384 students of 15 pedagogies from a university in Chile. The results show that homophobia and transphobia scores tend to be low in students of all careers. However, physical education students have the highest scores among all/future teachers, while biology, Spanish, English, history and geography students/students, Basic education and differential education have the lowest scores on one or both scales. It is concluded that there are differences in the levels of homophobia and transphobia according to the course, with the highest rates in physical education, although the scores of both scales are low.La homofobia y transfobia son sentimientos de rechazo y hostilidad hacia personas homosexuales y transgéneros, que surgen de prejuicios y miedos hacia la diversidad sexual. El objetivo de la presente investigación fue comparar los niveles de homofobia y transfobia de estudiantes de educación física y otras pedagogías de Chile. Para ello se aplicó la escala de homofobia EHF-10 y la escala de actitudes negativas hacia personas trans a 384 estudiantes de 15 Pedagogías de una universidad de Chile. Los resultados muestran que los puntajes de homofobia y transfobia tienden a ser bajos en los/as estudiantes de todas las carreras. Sin embargo, los/as estudiantes de educación física poseen los puntajes más altos entre todos los/as futuras docentes, en tanto, los/as estudiantes de biología, castellano, inglés, historia y geografía, educación básica y educación diferencial poseen los puntajes más bajos en una o ambas escalas. Se concluye que existen diferencias en los niveles de homofobia y transfobia según carrera cursada, con los índices más altos en educación física, aunque los puntajes de ambas escalas son bajos

Use of Immunostimulants in Shrimp Farming&mdash;A Bioeconomic Perspective

Aquaculture is the fastest-growing food industry worldwide because it allows faster intensive production in a limited space and short time. However, the trade-off of this production scheme has led to infectious disease outbreaks that harm food production with economic impacts. Immunostimulants have entered the industry to fight against diseases by enhancing the immune system and conferring better protection against pathogens. In this regard, dietary immunostimulants have been tested at the farm level, such as carbohydrates and proteins known to enhance immunity and improve survival rates under experimental conditions. Despite the success of immunostimulant inclusion in experimental aquaculture, economic evaluation is an innovative avenue to be integrated when a novel immunostimulant is developed. The bioeconomic analysis permits the accurate demonstration of advantages or disadvantages regarding survival and yield performance upon immunostimulant application through mathematical and statistical estimates. An integrative bioeconomic model for testing a novel immunostimulant should contemplate technological, biological, and economic submodels at least; thus, financial variables, such as revenue, costs, and profitability, should also be considered for proper decision-making. Therefore, this perspective briefly describes the most relevant immunostimulants used in shrimp farms and offers bioeconomic elements that should be considered for affordable immunostimulant development and inclusion in shrimp aquaculture