Is it possible to store spotted wolffish (Anarhichas minor) sperm by refrigeration?

Fish Physiology and Biochemistry - Spotted wolffish Anarhichas minor reproduction in captivity is dependent on in vitro fertilization. However, it is often challenging to acquire sufficient fresh...     

Is European catfish a threat to eels in southern France?

• 1. European eel (Anguilla anguilla) is recognized as a critically endangered species in the northern hemisphere. Threats such as overfishing or pollution are well known as risks for eel populations. However, much less is known about the impact of introduced fish on European eels. In particular, introduced large‐bodied predators could become new predators to eels.
• 2. The potential impact of European catfish (Silurus glanis L) on an eel population in the Camargue, southern France was studied using a combination of stable isotope and gut content analyses.
• 3. Only large‐bodied catfish (>500 mm) can consume numerous fish prey. However, catfish mostly consumed crayfish (Procambarus clarkii), these prey items being found in 79% of the guts of the largest individuals. Eel was absent from the dissected catfish guts. A mixing model based on Bayesian inference revealed that catfish diet included only 5% (0–8.5%) of marine sources (both eel and mullet).
• 4. While local economic interests prompted ecological studies to assess whether catfish exerted a new and strong predatory pressure on eel, this study found that European catfish behaved as an opportunistic omnivore, and as such was not a direct threat as a predator on eel populations in the Camargue. Copyright © 2011 John Wiley & Sons, Ltd.

     

Is the crown-of-thorns starfish a threat to the reefs of Lord Howe Island?

• 1 Lord Howe Island, a World Heritage Area which lies in the southern Pacific Ocean, has the most southern true coral reefs in the world.
• 2 In the past decade, populations of Acanthaster planci, the crown-of-thorns starfish, have significantly reduced coral cover at Elizabeth and Middleton Reefs, approximately 200 km to the north of Lord Howe Island, and a small population has been reported from Lord Howe Island.
• 3 The abundance and distribution of A. planci was evaluated using surveys by the local recreational diving industry and video-transects, and the potential rate of recovery of the coral community following predation was assessed by analysing coral recruitment patterns.
• 4 The starfish population at Lord Howe Island remained relatively small and localized between 1984 and 1993.
• 5 Coral recruitment was dominated by the juveniles of brooding corals, and these same species dominated the established coral community. There was limited recruitment of broadcast-spawning coral species during the study period, suggesting that southern dispersal of coral larvae from more northern sites may be a rare or sporadic event.
• 6 The results indicate that there is only a small probability that the present starfish population will result in a major starfish outbreak. However, the recovery of the coral community from a major outbreak would be slow because of the apparently low rate of input of coral larvae from sources external to the reef.
• 7 Management agencies need to consider whether the present small and localized starfish population should be removed, given the likely ramifications of an infestation and the economic importance of the reef to tourism.

     

Is the fast growth of an equatorial Micropterus salmoides population explained by high water temperature?

Britton JR, Harper DM, Oyugi DO. Is the fast growth of an equatorial Micropterus salmoides population explained by high water temperature? Ecology of Freshwater Fish 2010: 19: 228–238. © 2010 John Wiley & Sons A/S Abstract – Marginal increment analysis of scales collected from the introduced Micropterus salmoides population of Lake Naivasha, Kenya revealed the formation of an annual growth check, validating their use to age individual fish. Subsequent analysis of scales from 372 fish collected between 2002 and 2009 revealed individuals were very fast growing compared with native populations in North America and other introduced populations in Europe, South America, Africa and Asia. This was likely to be as a result of the water temperatures in Lake Naivasha exceeding 20 °C throughout the year. This was corroborated by a meta‐analysis of the growth parameters asymptotic length L_∞ and growth coefficient K from across their geographical range that revealed variance was explained by differences in mean annual air temperatures. At a break point of approximately 10 °C, there was a shift to reduced L_∞ and increased K, suggesting a temperature driven trade‐off between growth rate and ultimate length. When adjusted for temperature and weighted for sample size, there were significant differences between the growth parameters of the North American and introduced populations, suggesting that other abiotic and biotic variables were also important determinants of the growth of individuals between the two ranges.     

Freshwater ecosystem vulnerability: Is native climatic niche good enough to predict invasion events?

相似文献   

Molecular characterization and expression analysis of hypoxia-inducible factor-1α, factor-2α, and factor-3α and physiological response to hypoxia exposure in Amur minnow (Phoxinus lagowskii)

Aquaculture International - To further enhance our understanding of hypoxia tolerance in the fish Phoxinus lagowskii, hypoxia-inducible-factor (HIF) genes were cloned to analyze their biological...     

Is it a hindrance for an invasive aquatic species to spread across scattered habitat patches?

1. Despite their importance for aquatic biodiversity, ponds are among the most vulnerable freshwater habitats. Owing to their isolation in terrestrial environments, ponds are expected to be relatively well protected from biological invasions, but this depends on many factors. 2. The purpose of this study was to examine the influence of a range of variables (water quality, habitat, and landscape attributes) on the colonization of discrete ponds by a widespread aquatic invader, the red swamp crayfish Procambarus clarkii, which can disperse overland. 3. Investigations were conducted in two networks of ponds, each located in close proximity to a large invaded marsh. The two marshes under study differed in the length of time since the crayfish were introduced. 4. The proportions of colonized ponds and crayfish abundances were moderate in both networks, but higher in the network that had been invaded first. In both networks the distance to the marsh was the main predictor of pond colonization, considering similar energy costs to cross aquatic and terrestrial habitats for the recently invaded network, but assuming that dispersal was 25 times costlier across the terrestrial matrix than via streams for the earlier invaded network. Pond characteristics had no influence on crayfish occurrence in either network. Furthermore, predictions of pond invasion were lower for the recently invaded network. 5. The importance of the distance to the marsh indicates that natural dispersal was the main process of pond colonization by crayfish. Findings also suggested that overland dispersal was rare and costly. By contrast, streams were probably significant in facilitating crayfish dispersal. Differences between the two networks might arise from an invasion process still in progress in the recently invaded network. 6. From a management viewpoint, local actions are encouraged to prevent the spread of crayfish via streams. In addition, broader‐scale actions to mitigate other human disturbances would improve the outlook for pond biodiversity.     

Is it possible to successfully rear meagre (Argyrosomus regius Asso 1801) larvae without using rotifers?

In hatcheries, meagre Argyrosomus regius larvae still depend on an adequate supply of rotifers and Artemia, as no artificial diet can totally fulfil their nutritional requirements. However, production of live feed is highly expensive and demands intensive labour and specific facilities. This study investigated the effect of a dietary regime without the use of rotifers, to simplify the meagre larval rearing protocol. Two feeding treatments (T₁ & T₂) are compared to investigate their effects on survival and growth of meagre larvae. In T₁, larvae were fed rotifers from 2 to 5 days post hatch (dph), and Artemia from 4 to 15 dph. In T_2, larvae were kept under dark conditions and fed Artemia from 6 to 15 dph. Standard larval length (SL) was significantly higher in T₁ (p < .01) until 8 dph in comparison with larvae reared initially without rotifers. No significant difference in SL was found among treatments (p = .187) at 15 dph. Significant difference was found among treatments in survival rate at 15 dph (p < .003). The survival rate observed at 15 dph in T₂ (30 ± 4.2%) represents an important finding, although the highest survival rate was observed in T₁ (45.0 ± 3.4%). This study showed that it is possible to conduct larval rearing of meagre without using rotifers. Nevertheless, further research efforts are still needed to improve these results in comparison with the common larval rearing protocol.     

Is fisheries production within Large Marine Ecosystems determined by bottom‐up or top‐down forcing?

Understanding the mechanisms driving fisheries production is essential if we are to accurately predict changes under climate change and exploit fish stocks in a sustainable manner. Traditionally, studies have sought to distinguish between the two most prominent drivers, ‘bottom‐up’ (resource driven) and ‘top‐down’ (consumer driven); however, this dichotomy is increasingly proving to be artificial as the relative importance of each mechanism has been shown to vary through space and time. Nevertheless, the reason why one predominates over another within a region remains largely unknown. To address this gap in understanding, we identified the dominant driver of commercial landings within 47 ecosystems, encompassing a wide range of biogeochemical conditions and fishing practices to elucidate general patterns. We show that bottom‐up and top‐down effects vary consistently with past fishing pressure and oceanographic conditions; bottom‐up control predominates within productive, overfished regions and top‐down in relatively unproductive and under‐exploited areas. We attribute these findings to differences in the species composition and oceanographic properties of regions, together with variation in fishing practices and (indicative) management effectiveness. Collectively, our analyses suggest that despite the complexity of ecological systems, it is possible to elucidate a number of generalities. Such knowledge could be used to increase the parsimony of ecosystem models and to move a step forward in predicting how the global ocean, particularly fisheries productivity, will respond to climate change.     

Is observed variability in the long-term results of the Continuous Plankton Recorder survey a response to climate change?

In the more than 50 years that the Continuous Plankton Recorder (CPR) survey has operated on a regular monthly basis in the north-east Atlantic and North Sea, large changes have been witnessed in the planktonic ecosystem. These changes have taken the form of long-term trends in abundance for certain species or stepwise changes for others, and in many cases are correlated with a mode of climatic variability in the North Atlantic, either: (1) the North Atlantic Oscillation (NAO), a basin-scale atmospheric alteration of the pressure field between the Azores high pressure cell and the Icelandic Low; or (2) the Gulf Stream Index (GSI), which measures the latitudinal position of the north wall of the Gulf Stream. Recent work has shown that the changes in the GSI are coupled with the NAO and Pacific Southern Oscillation with a 2 year lag. The plankton variability is also possibly linked to changes observed in the distribution and flux of water masses in the surface, intermediate and deep waters of the North Atlantic. For example, in the last two decades, the extent and location of the formation of North Atlantic Deep Water, Labrador Sea Intermediate Water and Norwegian Sea intermediate and upper-layer water has altered considerably. This paper discusses the extent to which observed changes in plankton abundance and distribution may be linked to this basin-scale variability in hydrodynamics. The results are also placed within the context of global climate warming and the possible effects of the observed melting of Arctic permafrost and sea ice on the subpolar North Atlantic.     

What makes fish vulnerable to capture by hooks? A conceptual framework and a review of key determinants

Considerable time and money are expended in the pursuit of catching fish with hooks (e.g., handlining, angling, longlining, trolling, drumlining) across the recreational, commercial and subsistence fishing sectors. The fish and other aquatic organisms (e.g., squid) that are captured are not a random sample of the population because external (e.g., turbidity) and underlying internal variables (e.g., morphology) contribute to variation in vulnerability to hooks. Vulnerability is the probability of capture for any given fish in a given location at a given time and mechanistically explains the population‐level catchability coefficient, which is a fundamental and usually time‐varying (i.e., dynamic) variable in fisheries science and stock assessment. The mechanistic drivers of individual vulnerability to capture are thus of interest to fishers by affecting catch rates, but are also of considerable importance to fisheries managers whenever hook‐and‐line‐generated data contribute to stock assessments. In this paper, individual vulnerability to hooks is conceptualized as a dynamic state, in which individual fish switch between vulnerable and invulnerable states as a function of three interdependent key processes: an individual fish's internal state, its encounter with the gear, and the characteristics of the encountered gear. We develop a new conceptual framework of “vulnerability,” summarize the major drivers of fish vulnerability, and conclude that fish vulnerability involves complex processes. To understand vulnerability, a shift to interdisciplinary research and the integration of ecophysiology, fish ecology, fisheries ecology and human movement ecology, facilitated by new technological developments, is required.     

When to count your eggs: Is fecundity in Greenland halibut (Reinhardtius hippoglossoides W.) down-regulated?

Fecundity in several fish species is subjected to down-regulation by atresia so if fecundity is estimated many months before spawning, this will be an overestimation of the realised fecundity (actual number of eggs spawned). In order to get accurate measurements of fecundity it is important to have knowledge on when potential fecundity (estimated fecundity at time of sampling) closely resembles the realised fecundity. Down-regulation of fecundity for Greenland halibut (Reinhardtius hippoglossoides W.) was assessed using fish caught off East Greenland in 1998, 1999 and 2000. The fish caught in 1998 and 1999 were in early and late stages of vitellogenesis, respectively of the same maturation cycle. The fish caught in 2000 were also in an early stage of vitellogenesis. Fecundity decreased by 43% between early and late vitellogenesis. Fecundity in 1999 appeared to be the second lowest recorded for Greenland halibut but it is believed to be due to developmental stage rather than low productivity. There was no difference in fecundity between 1997 and 1998. It is believed that differences in fecundity between years only become apparent in late maturation as size during oocyte recruitment has a very large influence on fecundity. Neither Fulton's condition nor hepatosomatic index had any significant influence on fecundity.     

Is it good or bad to fish with FADs? What are the real impacts of the use of drifting FADs on pelagic marine ecosystems?

The use of fish aggregating devices (FADs) by purse seine fisheries has come under increasing criticism for its potential deleterious impacts on tuna stocks, for high levels of by‐catch and threats to the biodiversity of tropical pelagic ecosystems. Here, we review the current state of scientific knowledge of this fishing technique and current management strategies. Our intent is to encourage objective discussion of the topic and highlight areas worthy of future research. We show that catching juvenile tuna around FADs does not necessarily result in overfishing of stocks, although more selective fishing techniques would likely help obtain higher yield. Levels of non‐tuna by‐catch are comparable to or less than in other commercial tuna fisheries and are primarily comprised of species that are not considered threatened. Accordingly, to minimize impacts on ecosystem balance, there is merit in considering that all species captured in purse seine fisheries (excluding vulnerable species such as turtles and sharks) should be retained, but the consequences of such a measure should be carefully examined before implementation. The take of vulnerable species could be further reduced by introduction of additional mitigation measures, but their potential benefits would be limited without parallel efforts with other gears. Finally, there is no unequivocal empirical evidence that FADs represent an ‘ecological trap’ that inherently disrupts tuna biology although further research should focus on this issue. We encourage RFMOs to expand and improve their FAD management plans. Under appropriate management regimes, FAD fishing could be an ecologically and economically sensible fishing method.     

Is fertility of hybrids enough to conclude that the two oysters Crassostrea gigas and Crassostrea angulata are the same species?

The distinction of the two cupped oysters Crassostrea gigas (Thunberg, 1793) and Crassostrea angulata (Lamark, 1819) into two species was chiefly due to their differing geographical distributions, C. gigas being present in Asia and C. angulata in Europe. Today it is commonly accepted that C. angulata and C. gigas are a single species according to morphological, genetic and F1 hybridization data. However, the demonstration of the fertility of their hybrids and the absence of any reproductive isolation remained to be investigated. Consequently, we studied the fertility of hybrids and sperm competition by performing three different experiments and producing G1 and G2 hybrid progenies between wild populations of C. angulata and C. gigas. Progenies showed very close developmental yields, at 24 hours after fertilization, according to dam taxa suggesting a strong maternal transmission of oocyte quality, but no reproductive isolation was observed between the two taxa. Significant decreases of developmental yields were noticed in C. angulata females with sperm competition, most probably due to early larval mortality. The fertility of hybrids C. angulata × C. gigas was demonstrated, which is further evidence that they are the same species. To definitively state the precise taxonomic classification of C. angulata and C. gigas, further studies are needed to (i) identify geographical zones where these taxa are in contact and (ii) assess their level of hybridization in these zones.     

Can pH and Water-to-Protein Ratio be Good Instruments to Evaluate the Abusive Water Added in Seafood by Phosphate Addition?

The aim of the present study was to evaluate the effect of the phosphates on tuna meat pH, and water-to-protein ratio. Tuna fillets were soaked in cold (5 °C) tripolyphosphate solution (STPP) and blend phosphate (CARNAL® 961) at 3, 5 and 10% for 30, 60 and 120 min. The control group was represented by cold distilled water. After soaking, the samples were drained, weighed, frozen, stored (-35 °C, for 15 days), thawed, drained, and grilled. After each step, samples were withdrawn for the following analysis: pH, phosphate (as P2O5), moisture and protein. A gradual increase in pH and residual phosphate was observed, which remained below the limits established by national (for pH) and international (for phosphate) legislation. A moderate positive correlation between pH and phosphate values was observed. An increase in moisture content and the water-to-protein ratio were observed, and still below to the legislation limit (i.e., 6.0). We suggest a critical review and possible changes in the parameters which are used as indicators of abusive use of the phosphate additive in seafood to combat the economic fraud in the frozen seafood products. It should be emphasized that these suggestions should be the focus of the collaborative study for its validation.     

Is the use of recombinant cGnRH may be a future alternative to control the fish spawning? Let us go with the goldfish example

The use of recombinant gonadotropin-releasing hormone (rGnRH) has very rarely been tested in fish to promote spawning. This study evaluated the impact of recombinant chicken gonadotropin-releasing hormone (rcGnRH) with metoclopramide on the release of sex steroids and final maturation induction in goldfish (Carassius auratus) broodstock. For this purpose, goldfish broodstock was divided into four groups and treated with 0.9% NaCl with 20 mg/kg metoclopramide (Met) (C); 10 μg/kg body weight (BW) rcGnRH with 20 mg/kg metoclopramide (rcGn10); 15 μg/kg BW rcGnRH with 20 mg/kg metoclopramide (rcGn15); and 20 μg/kg BW rcGnRH with 20 mg/kg metoclopramide (rcGn20). The capability of the rcGnRH for eliciting biological response was tested in vivo by evaluating the changes of 17β estradiol (E2), testosterone (T), and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) and the induced spawning. Blood samples were obtained at 0 h, 12 h, and 24 h after injection. The rcGn10, rcGn15, and rcGn20 treatments induced lower E2 concentration, especially 24 h post-injection. T levels were significantly higher in rcGn10, rcGn15, and rcGn20 treatments 12 h post-injection than at 0 h and then decreased at 24 h post-injection. Furthermore, the rcGnRH tested significantly enhanced DHP secretion in rcGn10, rcGn15, and rcGn20 treatments 12 h post-injection before a decline at 24 h post-injection. No significant difference between the sampling times was found in the C treatment for the 3 sex steroids tested. The results also displayed that rcGnRH at 10–20 µg/kg of body weight can trigger spawning with the highest speed and efficiency of spawning at 20 µg/kg. The obtained results represent a possible strategy for enhancing the artificial reproduction and ovulation of broodstock fish by rGnRH and further support the use of recombinant hormones to promote reproduction in aquaculture.

     

Is Pseudanodonta complanata the most vulnerable of widespread European species of unionids? An intense stress test leading to a massive die‐off

相似文献