Reproductive resilience: a paradigm shift in understanding spawner‐recruit systems in exploited marine fish

A close relationship between adult abundance and stock productivity may not exist for many marine fish stocks, resulting in concern that the management goal of maximum sustainable yield is either inefficient or risky. Although reproductive success is tightly coupled with adult abundance and fecundity in many terrestrial animals, in exploited marine fish where and when fish spawn and consequent dispersal dynamics may have a greater impact. Here, we propose an eco‐evolutionary perspective, reproductive resilience, to understand connectivity and productivity in marine fish. Reproductive resilience is the capacity of a population to maintain the reproductive success needed to result in long‐term population stability despite disturbances. A stock's reproductive resilience is driven by the underlying traits in its spawner‐recruit system, selected for over evolutionary timescales, and the ecological context within which it is operating. Spawner‐recruit systems are species specific, have both density‐dependent and fitness feedback loops and are made up of fixed, behavioural and ecologically variable traits. They operate over multiple temporal, spatial and biological scales, with trait diversity affecting reproductive resilience at both the population and individual (i.e. portfolio) scales. Models of spawner‐recruit systems fall within three categories: (i) two‐dimensional models (i.e. spawner and recruit); (ii) process‐based biophysical dispersal models which integrate physical and environmental processes into understanding recruitment; and (iii) complex spatially explicit integrated life cycle models. We review these models and their underlying assumptions about reproductive success vs. our emerging mechanistic understanding. We conclude with practical guidelines for integrating reproductive resilience into assessments of population connectivity and stock productivity.     

A sensory and nutritional validation of open ocean mussels (Mytilus galloprovincialis Lmk.) cultured in SE Bay of Biscay (Basque Country) compared to their commercial counterparts from Galician Rías (Spain)

Mussel shell biometry, nutritional quality as well as consumer sensory evaluation of experimental open ocean cultured mussel Mytilus galloprovincialis (Lamarck 1819) were analyzed and compared to that of commercial mussels from Galician Rías available in the local market. Both mussel products were of the same commercial size. In this study, open ocean mussels were significantly higher and wider than those of Galician Rías. In addition, with the exception of ash content, both mussel products showed similar biochemical composition. Regarding fatty acid profiles, however, statistical differences were detected. These differences were not fully reflected in the sensory assessment. In terms of consumer acceptability, both mussel products were considered equally satisfactory.

     

Elasmobranch fisheries in the Arabian Seas Region: Characteristics,trade and management

The Arabian Seas Region plays an important role in the global landings and trade of sharks and rays. The United Arab Emirates (UAE) and Yemen, two countries with stark socio‐economic differences, serve as major regional trade hubs for shark and ray products and four countries (Oman, Pakistan, UAE and Yemen) supply nearly 11% of dried fin exports to Hong Kong. Yet, little information is available on the characteristics of this trade and the fisheries contributing to it. Here, we review the fisheries characteristics, trade, utilization and distribution chain of sharks and rays in 15 countries of the Arabian Seas Region based on published and grey literature, landing surveys, field observations and interviews with fishermen and traders. Although regional shark fisheries remain mostly artisanal, reported shark and ray landings represent 28% of the regional total fish production, reaching 56,074 mt in 2012 (7.3% of total world catches), with Iran, Oman, Pakistan and Yemen ranking as the primary catchers. Utilization and distribution patterns are complex, vary between landing sites and countries, and remain unmonitored. Based on widespread over‐exploitation of most teleost fisheries, current exploitation levels for most sharks and rays are potentially unsustainable. The situation is exacerbated by limited research and political will to support policy development, the incomplete nature of fisheries data, as well as insufficient regulations and enforcement. A better understanding of shark and ray fisheries will be key for regulating trade, promoting conservation and developing management initiatives to secure food security, livelihoods and biodiversity conservation in the region.     

Exogenous xylanase improves growth,protein digestibility and digestive enzymes activities in Nile tilapia,Oreochromis niloticus,fed different ratios of fish meal to sunflower meal

A 3 × 2 factorial experiment was designed to evaluate the effect of different ratios of fish meal (FM): sunflower meal (SFM) with or without exogenous xylanase supplementation on growth, feed utilization, digestive enzymes activities, apparent digestibility, intestinal and liver morphology and chemical composition of Nile tilapia, Oreochromis niloticus. Three isonitrogenous (329.80 g/kg of crude protein) and isoenergetic (18.46 MJ/kg gross energy) experimental diets were formulated as SFM₁ (FM:SFM = 2:1), SFM₂ (FM:SFM = 1:1) and SFM₃ (FM:SFM = 1:2) based on protein content. Each diet was supplemented with 0 or 0.5 g/kg of exogenous xylanase and was fed to triplicate groups of twelve fish (with initial weight, 1.31 ± 0.02 g) for 84 days. After 84 days of feeding period, the highest weight gain, specific growth rate, protein efficiency, protein productive value and the best feed conversion ratio were recorded in fish fed either SFM₁ or SFM₂ supplemented with exogenous xylanase. Whereas lowest growth performance was recorded in fish fed SFM₂ and SFM₃ un‐supplemented with xylanase. The highest activities of chymotrypsin, trypsin, lipase, amylase, alkaline phosphatase and cholecystokinin were observed in fish fed SFM₁ and SFM₂ diets supplemented with xylanase. The highest ADCs of dry matter, protein, lipid and digestible energy were recorded in fish fed SFM₁ and SFM₂ diets supplemented with exogenous xylanase. Supplementation of exogenous xylanase improved muscularis mucosa thickness, height of mucosal folds and enterocytes of intestinal fish. Addition of exogenous xylanase increased the calcium and phosphorus retention. Results of this study indicated that the addition of exogenous xylanase to diet containing high inclusion level of sunflower meal improved growth, digestive enzymes, nutrient digestibility, histological morphometric of liver and intestine and nutrient retention.     

Paraphoma root rot of alfalfa (Medicago sativa) in Inner Mongolia,China

Root rot symptoms were observed in fields of alfalfa in Chifeng city, Inner Mongolia, China in 2016. Disease incidences of seven alfalfa varieties planted in 2014 ranged from 56% to 95%, while incidence of Gongnong No. 1 planted in 2016 was 8%, 31% and 76% in 2016, 2017 and 2018, respectively. Paraphoma isolates were consistently recovered from black necrotic root tissues of diseased plants with a frequency of 77.1%. Based on morphological characters and phylogenetic analysis of rDNA internal transcribed spacer (ITS), elongation factor 1-α (EF1-α) and β-tubulin (TUB), this fungus was identified as Paraphoma radicina. Glasshouse pathogenicity experiments showed that P. radicina significantly reduced above- and below-ground biomass of alfalfa plants 2 months after inoculation. Paraphoma radicina infected 70% of the plants inoculated with a root dip in conidia, and these symptoms were consistent with the symptoms in the field. Paraphoma radicina was successfully reisolated from disease roots of the inoculated alfalfa plants. This is the first report of P. radicina as the causal agent of alfalfa root rot in China.