Length at Maturity, Sex Ratio, and Proportions of Maturity of the Giant Electric Ray, Narcine entemedor, in Its Septentrional Distribution

The size at which a certain fraction of a fish population reaches sexual maturity is an important parameter of life history. The estimation of this parameter based on logistic or sigmoid models could provide different ogives and values of length at maturity, which must be analyzed and considered as a basic feature of biological reproduction for the species. A total of 305 individuals of Narcine entemedor (N. entemedor) were obtained from artisanal fisheries in the Bahía de La Paz, Mexico. For the organisms sampled, sexes were determined and total length (TL) in cm was measured from October 2013 to December 2015. The results indicated that the females were larger, ranging from 48.5 cm to 84 cm TL, while males varied from 41.5 cm to 58.5 cm TL. The sex ratio was dominated by males ranging from 45–55 cm TL, while females were more abundant from 60 to 85 cm TL. Mature females were present all year long, exhibiting a continuous annual reproductive cycle. The length at maturity data were described by the Gompertz model with value of 55.87 cm TL. The comparison between models, and the model selection between them, showed that the Gompertz model had maximum likelihood and smaller Akaike information criterion, indicating that this model was a better fit to the maturity proportion data of N. entemedor.

Stronger density-dependent growth of Japanese sardine with lower food availability: Comparison of growth and zooplankton biomass between a historical and current stock-increase period in the western North Pacific

Density dependence is a fundamental concept for fish population dynamics. Although density-dependent growth and maturity among older juveniles and adults is important for regulating fish population size and for fisheries management, the mechanism of density dependence for marine fishes remains unclear. Here, we examined changes in Japanese sardine growth with increasing abundance beginning in the 2010s and how the current pattern of density-dependent growth differs from that of a previous stock-increase period from the 1970s to early 1980s. During the current period of increasing abundance, mean standard length has already dropped to the lowest level yet observed and growth has declined more sharply with increased abundance than in the 1970s and 1980s. Mesozooplankton biomass in July in the summer feeding grounds was also lower during the current period. Therefore, our results suggest that summer food availability in the western North Pacific controls the strength of density-dependent growth. A lower carrying capacity for Japanese sardine could account for the stronger density dependence of growth observed in the 2010s; this indicates that future Japanese sardine abundance might not increase as much as in the 1980s unless food availability improves.

Characterizing the genetic basis of trait evolution in the Mexican cavefish

Evolution in response to a change in ecology often coincides with various morphological, physiological, and behavioral traits. For most organisms little is known about the genetic and functional relationship between evolutionarily derived traits, representing a critical gap in our understanding of adaptation The Mexican tetra, Astyanax mexicanus, consists of largely independent populations of fish that inhabit at least 30 caves in Northeast Mexico, and a surface fish population, that inhabits the rivers of Mexico and Southern Texas. The recent application of molecular genetic approaches combined with behavioral phenotyping have established A. mexicanus as a model for studying the evolution of complex traits. Cave populations of A. mexicanus are interfertile with surface populations and have evolved numerous traits including eye degeneration, insomnia, albinism and enhanced mechanosensory function. The infertility of different populations from the same species provides a unique opportunity to define the genetic relationship between evolved traits and assess the co-evolution of behavioral and morphological traits with one another. To define the relationships between morphological and behavioral traits, we developed a pipeline to test individual fish for multiple traits. This pipeline confirmed differences in locomotor activity, prey capture, and startle reflex between surface and cavefish populations. To measure the relationship between traits, individual F2 hybrid fish were characterized for locomotor behavior, prey-capture behavior, startle reflex and morphological attributes. Analysis revealed an association between body length and slower escape reflex, suggesting a trade-off between increased size and predator avoidance in cavefish. Overall, there were few associations between individual behavioral traits, or behavioral and morphological traits, suggesting independent genetic changes underlie the evolution of behavioral and morphological traits. Taken together, this approach provides a novel system to identify genes that underlie naturally occurring genetic variation in morphological and behavioral traits.

Indigenous Fishing Methods of the Moyon Tribe of Manipur (India) and Myanmar

Fishing is one of the main economic activities of the Moyon tribe living in Manipur (India), and Myanmar. For many centuries, Moyons used indigenous methods for fishing. However, in recent years, indiscriminate fishing using modern technologies has led to an ecological crisis which not only affected the ichthyofauna diversity but also affected the livelihood of individuals depending on fishing as well as the sustainability of the indigenous fishing methods. The paper explores the indigenous fishing techniques and practices of the Moyon tribe. The study adopted a qualitative-exploratory research method with ethnography as the primary component. Data were collected from on-site observations of fishing and discussions with the local Moyon population. The study revealed that indigenous fishing methods have become unsustainable due to misuse by the fishers. Another significant observation was the shift in fishing methods from traditional to modern (market) gears. The recently used fishing gears are a threat to the fish population, aquatic ecosystem, and indigenous knowledge of fishing crafts. The study concludes that unsustainable fishing by the Moyon tribe is connected with poverty and the lack of development and education.

Using a climate attribution statistic to inform judgments about changing fisheries sustainability

Sustainability—maintaining catches within the historical range of socially and ecologically acceptable values—is key to fisheries success. Climate change may rapidly threaten sustainability, and recognizing these instances is important for effective climate adaptation. Here, we present one approach for evaluating changing sustainability under a changing climate. We use Bayesian regression models to compare fish population processes under historical climate norms and emerging anthropogenic extremes. To define anthropogenic extremes we use the Fraction of Attributable Risk (FAR), which estimates the proportion of risk for extreme ocean temperatures that can be attributed to human influence. We illustrate our approach with estimates of recruitment (production of young fish, a key determinant of sustainability) for two exploited fishes (Pacific cod Gadus macrocephalus and walleye pollock G. chalcogrammus) in a rapidly warming ecosystem, the Gulf of Alaska. We show that recruitment distributions for both species have shifted towards zero during anthropogenic climate extremes. Predictions based on the projected incidence of anthropogenic temperature extremes indicate that expected recruitment, and therefore fisheries sustainability, is markedly lower in the current climate than during recent decades. Using FAR to analyze changing population processes may help fisheries managers and stakeholders to recognize situations when historical sustainability expectations should be reevaluated.

Non-Indigenous Parasites of Fish in Inland Waters of Croatia

Non-indigenous parasite fauna of freshwater fish has not been studied extensively in Croatia, despite the long history of introductions and translocations of alien fish species into inland waters. Negative implications for aquaculture production and wild native fish species have been frequently associated with the introduction of non-native parasite species. Hence, the present paper attempts to lay out a historical overview of the suspected localities, time frames and pathways of introduction for non-indigenous fish parasites into inland waters of Croatia, therefore producing a list of species. In total, 16 non-native fish parasites have been recorded in inland waters of Croatia, aquaculture establishments being identified as initial points of introduction. However, a paucity of information exists on the overall prevalence of infection as well as the economic impact on aquaculture production. In addition, limited information is available about the presence and potential ecological impact of non-indigenous parasites on endemic fish fauna in areas of high biodiversity, such as the water bodies of the Adriatic Sea Basin. Therefore, there is an urgent need and opportunity for multidisciplinary cooperation between different stakeholders, including government, scientists, in both biological and veterinary disciplines, and the industry, with the aim of extensive surveys to determine the potential impact on aquaculture production and wild fish population of high conservation value.

Characterization of the Ichthyological Population of Hydrosystèmes in the Lagoon Area of the Azagny National Park (Ivory Coast)

The conservation of protected areas is nowadays one of the concerns of international and national institutions. This study aims to contribute to better conservation of the ichthyological fauna of the lagoon area of the Azagny National Park (PNA). This national park has been dealing with the harmful effects of human activities for years. Thus, from March 2019 to February 2020, sampling campaigns were carried out to characterize this space, for better conservation. The results obtained are based on the analysis of abiotic and biotic (fish) data collected at 6 stations. The physicochemical parameters were measured using a multiparameter and the fish population collected using 10 gillnet batteries of 10, 25, 30, 35, 40 and 50 mm mesh void. The analysis of the ichthyological population of the lagoon area reveals a diversity of 53 species belonging to 30 families and 12 orders. 11 species were newly collected while 31 species previously recorded in these hydrosystems were not captured in the present study. The Shannon (H’> 2) and Equitability (E> 0.5) indices calculated reflect a good organization and stability of the ichthyological population of the hydrosystems of the PNA lagoon zone. The Monte-Carlo test indicates that the variables rate of nitrate, width, rate of dissolved oxygen, water temperature, alkalinity, salinity, rate of dissolved solid and phosphorus are those which discriminate specific richness, abundance and the distribution of the stand.

Population parameters of several groupers (Famili Serranidae) in Labuan Bajo waters, East Nusa Tenggara

Labuan Bajo has a fertile aquatic ecosystem, one of them is the coral reef ecosystem. This condition happened because of the supply of nutrients that are carried through Indonesia Through Flow and the local upwelling phenomena. Various species of reef fish of various sizes have been caught in Labuan Bajo waters. In general, the type of reef fish that dominates is grouper fish catch by using handline fishing gear. Furthermore, there is damage that occurs in the coastal ecosystem causes changes in ecological functions and disrupted ecosystem benefits. In addition, pressure from overuse did not provide opportunities for resources to carry out recovery makes the condition of resource stocks threatened. This study aims to determine the parameter aspects of the population of several types of grouper fish in Labuan Bajo waters. The types of grouper studied included Plectropomus leopardus, P. maculatus, P. oligacanthus, and Variola albimarginata. Data collection was carried out by enumerators from April to August 2019 which included the daily data on the length and weight distribution of groupers. Length-frequency distribution data is analyzed by estimating fish population parameters using the Electronic Length Frequency Analysis (ELEFAN I) program which is packaged in the FAO-ICLARM Stock Assessment Tool II (FiSAT II) software. The results of the analysis showed the equation of growth parameters for Von Bartalanffy for P. leopardus is Lt = 89.06(1-e−0.24(t+0.52)); P. maculatus is Lt = 76(1-e−0.54(t+0.23)); P. oligacanthus is Lt = 72.32(1-e−0.66(t+0.19)); and V. albimarginata is Lt = 45(1-e−0.51(t+0.29)). The length at first birth of each species is Lt=0 P. leopardus = 10.45 cm, Lt=0 P. maculatus = 8.88 cm, Lt=0 P. oligacanthus = 8.52 cm, and Lt=0 V. albimarginata = 6.19 cm. Meanwhile, the exploitation rate (E) of P. leopardus, P. maculatus, P. oligacanthus, and V. albimarginata were 0.81; 0.53; 0.45; and 0.70.

Diversity of fish fauna in the Sembakung river, North Kalimantan, Indonesia

Sembakung river is an important inland fishery in terms of fish production in North Kalimantan, Indonesia. This river is connected to the State of Malaysia, where the upstream part of this river is in the state of Malaysia. The present study was conducted to inform the diversity of fish fauna in the Sembakung river. Fish samples were collected from ten sampling stations of the Sembakung river at Tarakan district in North Kalimantan, Indonesia from March to November 2019. A total of 55 species of fish under 20 orders and 35 families were recorded. Cypriniformes were most leading order constituting 32.73% of the total fish population followed by Siluriformes (18.18%), Anabantiformes (10.91%), Gobiiformes (9.09%), Carangaria (5.45%), Eupercaria (3.64%), and 1.82% for others ordo. Fishes in this river are seriously affected by the various kinds of human development interventions and activities, especially in the areas of agriculture, forestry, fisheries, industries, and transport. Estimates from these indices were indications of low fish species composition and richness and unevenness in the population of fish in the Sembakung river. For sustainability of fishery resources, an adequate knowledge of species composition, diversity, and relative abundance of water bodies must be understood and vigorously pursued. Therefore, there is a need for the conservation and sustainable management of the fisheries resources of the Sembakung water body by relevant agencies.