Abstract Marine biota is a great source of ecosystem services. Recently, the involvement of marine organisms in biotechnological applications has been discovered and become useful for the development of alternative and healthy food, natural medicine and cosmetics. The most known ecosystem service is the provision of seafood; however, fishery management has to be implemented in order to avoid fishing exploitation, depletion of the sea and assure the recruitment by fish larva. This review put in relation the role of zooplankton in the ecosystem and its importance in fish recruitment. Zooplankton and fish are close connected; indeed, their prey-predator relation is an important factor for fish recruitment. Understanding the dynamic and trophic relation among different groups (phytoplankton – zooplankton – fish) and the ecosystem services they give to us, may increase the awareness of the importance to preserve marine environments. Furthermore, this relation is also important for fish aquaculture practices, as it is discussed in the present review. Further researches on potential zooplankton species that may be involved in fish farms may also ameliorate aquaculture services. To preserve the seas from fish depletion and to assure seafood provision, it is fundamental to have deep knowledge about the ecological connections in the marine environment and to obtain fishery management respectful for the environment.
An extremely variegated picture of harmful algal bloom types and their socio-economic impacts at the regional and subregional scale emerges from the overviews presented in this special issue. The diversity of the HAB events parallels that of the causative species, which show different ranges and ecological characteristics, as well as highly variable responses to environmental changes. The intensity and frequency of specific blooms vary at regional and local scale, with increasing or decreasing trends and sudden occasional outbursts, but with no general uniform trend that can be discerned from that of increased observational efforts. In many cases intoxications and other adverse effects on human health are kept under control through increased monitoring activities, but impacts on human activities such as aquaculture, fishery, use of natural marine resources and tourism keep on posing economic activities at risk in many regions.
Annastaycya Simsang Sangma, Biswajit Lahiri, Amitava Ghosh
et al.
Angling tourism is gaining popularity and offers an alternative livelihood opportunity for the fish farmers of the Garo Hills region of Meghalaya, India. This research aims to provide insights into the social value of angling tourism among the fish farmers involved in angling tourism in the area and to identify its determinants. A sample of one hundred fish farmers was selected using snowball sampling from five districts of the Garo Hills, and data were collected using a semi-structured interview schedule. Most farmers considered fisheries a secondary occupation and were sceptical of angling tourism. The multiple stepwise regression analyses revealed that entry fees for daily angling besides competition and secondary occupation negatively impacted social value scores. In contrast, the educational status of fish farmers, annual investment in angling tourism, fish farming experience, total registered anglers annually, and family type positively impacted social value scores. The study confirmed that angling tourism fosters sustainable development within rural communities by nurturing social values and augmenting biodiversity conservation, and economic benefits. Overall, the study provides valuable information on the scope and prospects of angling tourism in leveraging social values and its potential to uplift rural people's social and financial status.
Vinícius Pereira da Silva Oliveira, Danilo da Silva Borges, Erick de Moraes Franklin
Fluidized beds consist of solid particles suspended in a tube by an ascending fluid. In liquids, it is not rare that particles adhere to each other, decreasing the solid-liquid contact area and the ratio between the tube and grain diameters, deteriorating fluidization. We inquire into this problem by carrying out experiments with trios of spheres fluidized by water flows, the spheres being glued in predefined angles. In our tests, we used a 25.4-mm-ID (internal diameter) tube and 5.95-mm-diameter spheres, and we varied the angle of trios within 60$^{\circ}$ and 180$^\circ$ and water velocities within 0.027 and 0.210 m/s. Due to the small ratio between the diameters of the tube and spheres (approximately 4.3), the bed is prone to the formation of plugs and clogs. Our experiments show that elutriation, fluidization with plugs, glass transitions (amorphous static structures), packed beds, clogging, and a transitional clogged-plug regime can appear in the bed, depending on the bonding angles and water velocities. We report the relations between the bed height, bonding angles, and flow velocity, and show that they correlate with the granular temperature. We also show that an angle of 90$^\circ$ maximizes fluidization for a given fluid velocity, and we propose a regime map that organizes the different patterns based on the bonding angle and flow velocity. The proposed map can serve as a guide for selecting the fluid velocities in order to keep the bed fluidized at all times, helping in the design and operation of fluidized beds.
The autor considers an initial-boundary value problem for the nonstationary Stokes system in an angle, where Dirichlet and Neumann conditions are prescribed on the diferent sides of the angle. The major part of the paper deals with the parameter-depending problem which arises after the application of the Laplace transform. The author obtains existence, uniqueness and regularity results for this problem in a class of weighted Sobolev spaces. Using the properties of the Laplace transform, he proves the existence and uniqueness of strong solutions of the time-dependent problem.
Abstract Six 0.1‐ha earthen ponds with 45 kW/ha of aeration capacity were stocked with hybrid catfish (Ictalurus punctatus x I. furcatus) ranging from 15,000 to 90,000 fish ha−1 in 15,000 fish ha−1 increments to analyze the effect of nitrogen loading on ammonia accumulation and fish production. Minimum dissolved oxygen (DO) concentration was maintained above 3.0 mg O2 L−1 to prevent hypoxia‐induced appetite reduction. Stocking density did not impact survival but decreased average fish harvest weight and increased food conversion ratio (FCR). Gross production increased with stocking density and ranged from 7249 to 35,674 kg ha−1. Average total (TAN) and un‐ionized ammonia (NH3) were not different among stocking densities despite greater nitrogen inputs in ponds with higher feeding rates. Nitrite (NO2−) and nitrate (NO3−) concentrations were significantly higher in ponds with higher stocking densities, suggesting that nitrification increased with nitrogen loading. Phytoplankton assimilation of ammonia is the primary ammonia removal process in traditional catfish ponds with modest fish densities and feeding rates. However, in intensively aerated ponds with high feeding rates, nitrification can become an important process for ammonia removal. These data indicate that small earthen hybrid catfish ponds with high aeration capacities can increase catfish production without ammonia accumulating.
Serena Sanders, Thane A. Militz, Paul C. Southgate
ABSTRACT Expansion of pearl production using the silver‐lip pearl oyster, Pinctada maxima, depends on increasing the availability of high‐quality spat from hatcheries and optimization of existing hatchery protocols. Research to develop feeding regimes yielding higher quality spat is seen as a priority. This study evaluated the suitability of three microalgae (Rebecca salina, Chaetoceros simplex and Tisochrysis lutea), fed singly and in combination, for spat of P. maxima and assessed whether mixed diets yielded spat of higher quality. A model‐fitting approach examined the response of spat fed microalgal diets for 35 days. Organic content of spat, as an indicator of quality, as well as metrics relating to spat size and weight were considered. On the basis of organic content, all microalgal diets tested were found suitable and there was no evidence that the mixed diets yielded higher quality spat compared to monospecific diets. Further, any gains in spat size attributed to the mixed microalgal diets were comparatively modest. Contrary to long‐held assumptions, our results indicate that monospecific microalgal diets are not necessarily inferior to mixed microalgal diets for on‐growing spat of P. maxima. They indicate potential to develop simpler and cheaper protocols for culture of P. maxima spat in land‐based systems.
Aleksander Sanjuan Ciepielewski, Jakub Tworzydło, Timo Hyart
et al.
Magic-angle twisted bilayer graphene is a tunable material with remarkably flat energy bands near the Fermi level, leading to fascinating transport properties and correlated states at low temperatures. However, grown pristine samples of this material tend to break up into landscapes of twist-angle domains, strongly influencing the physical properties of each individual sample. This poses a significant problem to the interpretation and comparison between measurements obtained from different samples. In this work, we study numerically the effects of twist-angle disorder on quantum electron transport in mesoscopic samples of magic-angle twisted bilayer graphene. We find a significant property of twist-angle disorder that distinguishes it from onsite-energy disorder: it leads to an asymmetric broadening of the energy-resolved conductance. The magnitude of the twist-angle variation has a strong effect on conductance, while the number of twist-angle domains is of much lesser significance. We further establish a relationship between the asymmetric broadening and the asymmetric density of states of twisted bilayer graphene at angles smaller than the first magic angle. Our results show that the qualitative differences between the types of disorder in the energy-resolved conductance of twisted bilayer graphene samples can be used to characterize them at temperatures above the critical temperatures of the correlated phases, enabling systematic experimental studies of the effects of the different types of disorders also on the other properties such as the competition of the different types of correlated states appearing at lower temperatures.
S. S. Savchenko, D. A. Morozova, S. G. Jorstad
et al.
Observations of quasars show that the polarization position angle of the emission coming from them varies greatly over time, including periods called rotations during which the angle changes in an orderly manner. The study proposes a method for identifying such events and assessing their statistical significance. The operation of the method is demonstrated using the example of long-term polarimetric observations of the blazars CTA 102, 3C 454.3, and OT 081. During the analysis of light curves, 51 rotations of the polarization position angle were found and it was shown that for CTA 102 and 3C 454.3 the rotations are predominantly oriented in one direction.
Fish species distribution in Lake Lebedinoye is considered. The samples were collected by fry seine along entire coast of the lake. Ten species of fish were sampled in the coastal zone; juveniles of chum salmon Oncorhynhus keta, amur stickleback Pungitius sinensis, and japanese dace Tribolodon hakonensis were rather abundant, other species were few in number. Japanese huchen Parahucho perryi were noted among the latter species: both juveniles of different age and an adult specimen of ≈ 2 kg weight were caught.
Chinasa Sylvia Onyenekwe, Daniel Bruce Sarpong, Irene Susana Egyir
et al.
There is overwhelming evidence to suggest that climate shocks undermine food security and livelihood well-being of the climate-impacted Niger Delta region of Nigeria. Employing survey data collected from farming and fishing households in the Niger Delta region of Nigeria, the study investigated the range of adaptation practices prevalent in the region, as well as factors influencing the adoption of these adaptation strategies. Five hundred and three (503) households (252 fishing households and 251 farming households) were selected using multi-stage sampling techniques. Multinomial logit model was used to determine factors affecting the household choice of adaptation strategies. The results show that adaptation strategies adopted by farming households were livelihood diversification (78.5%), crop management (77.7%), and soil and water management (64.5%). Factors influencing their choice of adaptation strategies were age, gender, household size, education, extension, and farm size. The adaptation strategies employed by the fishing households were livelihood diversification (83.61%) and intensification [which include the use of improved fishing gears (80.33%), varying fishing locations (67.21%), and expanding area of fishing (40.98%)]. Uncovering the heterogeneity in adaptation and resilience aspects to climate shocks has immense practical significance, particularly in providing targeted assistance for the two livelihood groups' adoption.
In this study, two kinds of shark repellents, chemical shark repellent and electric pulse shark-repelling device were selected to test their effects on seawater quality as well as the physiology and survival of fish using simulated ecology experiments. Three marine fish species, Japanese flounder (Paralichthys olivaceus), black rockfish (Sebastes schlegelii), and spotted grouper (Oplegnathus punctatus) were selected as test subjects. The results of water quality indicators showed that the chemical shark repellent could significantly reduce the water transparency and pH (P < 0.05), while the electric pulse shark-repelling device had no significant effect. The mortality rate of the fishes under the chemical shark repellent was 100% within 15 min, while it was 0% under both the electric pulse shark-repelling device and the blank control. While investigating the effect of the two repellent methods on the survival and physical activities, the gills and fins of juvenile fish in the chemical shark repellent group were rapidly dyed blue reaching a mortality rate of 100% within 15 min, while the juvenile fish in the electric pulse shark-repelling device group resumed their natural activities rapidly except for exhibiting avoidance behavior when the device was started. The blood indices of the species did not show any significant differences in the chemical shark repellent group because of the acute mortality caused by poisoning. However, in the electric pulse shark-repelling device group, the number of erythrocytes and leukocytes significantly increased in all three fishes. In terms of blood biochemical indices, the chemical shark-repellents caused a significant increase in chloride content, blood glucose, and alkaline phosphatase (AKP) enzyme activity in the juvenile fishes, while the blood albumin content reduced significantly in all three fishes. The use of electric pulse shark-repelling device caused a significant increase in blood glucose and glutamate transaminase activity only in the Japanese flounder. Histopathological results showed that chemical shark repellents caused tissue damage to the gill, liver, spleen, and heart in juvenile fishes. It can be seen that compared to chemical shark repellents, the electric pulse shark-repelling device is a more environmentally friendly way to repel sharks as it has less impact on seawater quality as well as less toxic effects on major marine fishes. These results would provide a scientific basis for the selection of shark repellent methods in ocean exploration activities.
Xiaomei Li, Aaron D. Ratschow, Steffen Hardt
et al.
Slide electrification - the spontaneous charge separation by sliding water drops - can lead to an electrostatic potential of 1 kV and change drop motion substantially. To find out, how slide electrification influences the contact angles of moving drops, we analyzed the dynamic contact angles of aqueous drops sliding down tilted plates with insulated surfaces, grounded surfaces, and while grounding the drop. The observed decrease in dynamic contact angles at different salt concentrations is attributed to two effects: An electrocapillary reduction of contact angles caused by drop charging and a change in the free surface energy of the solid due to surface charging.
1.Institute of Marine Sciences, Faculty of Marine Sciences & Fisheries, University of Chittagong, Bangladesh. 2.Department of Fisheries and Marine Science, Noakhali Science and Technology University, Bangladesh. 3.School of Engineering and Built Environment, Griffith University, Brisbane, Queensland, Australia. 4.Department of Aquaculture, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh. 5.Faculty of Fisheries and Food Science, Universiti Malaysia Terengganu, Kuala Nerus, Terengganu, Malaysia. 6.Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, BE 1410, Brunei Darussalam. Corresponding Author: a.habib@umt.edu.my; mbhnstu@gmail.com ________________________________________________________________________________________
Francisco J. Martín-Vega, Gerardo Gómez, David Morales-Jiménez
et al.
Directional beamforming will play a paramount role in 5G and beyond networks in order to combat the higher path losses incurred at millimeter wave bands. Appropriate modeling and analysis of the angles and distances between transmitters and receivers in these networks are thus essential to understand performance and limiting factors. Most existing literature considers either infinite and uniform networks, where nodes are drawn according to a Poisson point process, or finite networks with the reference receiver placed at the origin of a disk. Under either of these assumptions, the distance and azimuth angle between transmitter and receiver are independent, and the angle follows a uniform distribution between $0$ and $2π$. Here, we consider a more realistic case of finite networks where the reference node is placed at any arbitrary location. We obtain the joint distribution between the distance and azimuth angle and demonstrate that these random variables do exhibit certain correlation, which depends on the shape of the region and the location of the reference node. To conduct the analysis, we present a general mathematical framework which is specialized to exemplify the case of a rectangular region. We then also derive the statistics for the 3D case where, considering antenna heights, the joint distribution of distance, azimuth and zenith angles is obtained. Finally, we describe some immediate applications of the present work, including the analysis of directional beamforming, the design of analog codebooks and wireless routing algorithms.
The moving contact-line problem is of both theoretical and practical interest. The dynamic contact angle changes with the capillary number defined by the contact-line speed, and the correlation also depends on the equilibrium contact angle measured at the static state. This correlation is usually required as an input to the traditional solvers based on the Navier-Stokes-like equations, but it is simulated as an output in the current study using the lattice Boltzmann method (LBM) in a displacement process of two-immiscible fluids. The macroscopic theory and the molecular dynamics (MD) simulation had shown a linear scaling law for the cosine of dynamic contact angle, which is also observed in the previous LBM study in a short range of small capillary numbers and for two neutral wetting conditions. However, our study shows that this linear scaling law holds in the whole range of capillary numbers and is universal for all wetting conditions. In a special case of complete wetting (spreading) with a zero equilibrium contact angle, a thin film of the wetting fluid occurs when the wettability is very strong, which leads to a hysteresis that substantial capillary number is required to initiate the deviation of the dynamic contact angle from its equilibrium state. This observation is consistent with the previous report on a new mechanism for the static contact angle hysteresis due to the presence of free liquid films. With an increasing capillary number, the fluid-fluid interface starts oscillating before fingering. Different fingering patterns are observed for cases with different equilibrium contact angles.
Surmounting evidence supports that infectious agents play a critical role in shaping fish physiology, behaviour, and survival. The exclusion of disease-causing agents from fisheries research has resulted in major knowledge gaps that may limit the predictive capacity of ecological models. A major barrier in wild fisheries epidemiology is the logistical constraints associated with observing disease and obtaining samples from free-ranging fish, restricting the vast majority of research to laboratory studies or aquaculture facilities. For fisheries ecologists, including infectious agents can provide greater insight into observed phenomena, particularly with respect to fish physiology (e.g., metabolism), movement (e.g., migration rates), behaviour (e.g., habitat selection), personality (e.g., bold versus shy), and survival. Here we provide a brief introduction to the current understanding of disease ecology in wild fish and describe technological advances in both epidemiology and fisheries and aquatic sciences that can be used in tandem to create comprehensive studies of disease ecology in wild fishes. Combining nonlethal sampling and molecular genetic-based identification methods with field studies creates vast opportunities for innovative study designs that have the potential to address the true complexity of aquatic ecosystems.
Abstract Fish consumption can reduce malnutrition in many fish-producing low-income countries. Despite concerted efforts to develop capture fisheries and aquaculture in many low-income countries, fish demand remains poorly understood due to weak and fragmented domestic markets, particularly in sub-Saharan Africa. An important area that affects their development is limited understanding of the complementarities and trade-offs in choice and demand for fish products and how the choice and demand for fish products are affected by the socioeconomic characteristics of consumers, market factors and fish-specific attributes. Previous studies have assessed consumer choice and demand for fish in general, without considering species-specific consumer choices. We add to the literature by analyzing complementarity and trade-offs in consumer choice and demand for fresh and smoked/dried products of two tilapia species, Lake Malawi Oreochromis (Nyasalapia) spp. and Oreochromis shiranus using household survey data from urban Malawi. We employ Multivariate Probit and Seemingly Unrelated Regression models to analyze the correlates and complementarities and trade-offs in consumer choice and demand. Regression results indicate trade-offs in choices but complementarities in demand for tilapia products. We find that the correlates of choice are not the same as correlates of demand. Sex and years of schooling of the food decision maker, frequency of fish consumption, household income, access to fish price and market information, tilapia price and traits significantly influenced consumer choice and demand. Developing robust tilapia value chains requires exploiting the complementarities and trade-offs and policy support to boost tilapia production, lower prices and increase access to fish price and market information. More generally fish breeding programs should also link breeding objectives to consumer choices and demand for fishery products, particularly considering the rarely examined fish attributes such as ease of cooking, appearance, taste, and smell.