Perinatal hypoxia induces subsequent retinal degeneration in the offspring of ovoviviparous fish, Xiphophorous maculates

OBJECTIVE: This experiment evaluated the perinatal hypoxic effect on the retina of offspring of the ovoviviparous fish. ANIMAL STUDIED: The ovoviviparous fish Xiphophorous maculates was used for the experiment. PROCEDURE: The mothers were kept in a hypoxic environment of 3.5% oxygen for 6 h, starting 30 h before hatching. Subsequently, the retinae of the offspring were fixed, sectioned at 6 microm and evaluated microscopically from the age of 1 to 35 days. RESULTS: Degeneration of the outer nuclear layer of the retina was noted on the 3rd day and severe retinal degeneration was observed on the 35th day. Immunocytochemistry confirmed apoptosis by TUNEL reaction. There was no difference in neovascularization, as revealed by vascular endothelial growth factor, between controls (group 1) and hypoxic fish (group 2). CONCLUSIONS: Perinatal hypoxia could have long-lasting effects on the central nervous system in some species.     

Recent changes in the trophic structure of the Black Sea

During the past few decades, the Black Sea has been subjected to various human impacts that have led to changes in the ecology of this inland sea. River runoff has introduced high levels of certain heavy metals and other toxic substances as well as detergents. Ship traffic has led to the introduction of new species, and fishing pressures have also altered the ecology of the area.
This paper reviews major ecological changes over the past 40 years. An increase in nutrients has caused eutrophication, with outbursts of phytoplankton blooms and changes in the species composition of these algae. Small-sized zooplankton species and gelatinous zooplankton have become more common, while many of the herbivorous copepods have decreased in abundance or have disappeared. The introduction of the predatory ctenophore Mnemiopsis leidyi in the 1980s has had significant impact on the plankton community and has led to a sharp decline in anchovy stocks. Decreased water transparency has led to a loss of macrophytic algae, except in shallow waters, and to a subsequent decline in the zoobenthos associated with this flora. Eutrophication has also led to decreased oxygen concentrations in the near-bottom water due to large amounts of decomposing phytoplankton, and regions of hypoxia and anoxia now appear on the shelf, with consequent reduction in benthic populations of invertebrates and demersal fish. The numbers of fish species harvested commercially have fallen from 26 to 5, but the total catch has increased, owing to increases in abundance of small fish (e.g., sprat) and horse mackerel, and to increased fishing effort.     

Seasonal spatial distribution of juvenile lake sturgeon in Muskegon Lake,Michigan, USA

We examined seasonal spatial distribution and diel movements of juvenile lake sturgeon Acipenser fulvescens in Muskegon Lake, Michigan (a protected, drowned river mouth lake that links the Muskegon River to Lake Michigan). We surgically implanted ultrasonic tags in 20 juveniles (age 1–7) captured in gill nets to track their locations during August–December 2008/2009 and September 2010–October 2011. Most juveniles were observed ≤1.5 km from the mouth of the Muskegon River in Muskegon Lake at a mean depth of 7.5 m (SE = 1.3 m) during summer. In fall, juveniles moved away from the river mouth to the deepest part of Muskegon Lake and were observed at a mean depth of 15.8 m (SE = 1.3 m) during winter. The shift in spatial distribution coincided with fall turnover (i.e., loss of thermal stratification) and with changes in dissolved oxygen (DO) concentrations in the hypolimnion. During summer, DO concentrations in the hypolimnion were typically <4 mg·l^?1 in the deepest part of Muskegon Lake and DO concentrations at locations of tagged lake sturgeon were >7 mg·l^?1 in 94% of instances. Tracking in 2009 revealed no significant change in depth distribution or movement over the diel cycle. We only observed two tagged juveniles immigrating to Lake Michigan, suggesting that juveniles use Muskegon Lake for multiple years. Our results suggest that: (i) Muskegon Lake serves as an important nursery habitat for juvenile lake sturgeon that hatched in the Muskegon River before they enter Lake Michigan and (ii) seasonal changes in DO concentration in the hypolimnion likely affect the spatial distribution of juveniles in Muskegon Lake.     

Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya Bay

• 1. Ariake Bay, which is located in western Japan, has a large tidal range (>6 m) and a vast tidal flat (200 km²). In the early 1990s, the government‐managed Isahaya Reclamation Project began in the western part of Ariake Bay. A 16‐km² area of tidal flat in the inner part of Isahaya Bay was destroyed through reclamation and separated from the sea by a dyke, which created land and a freshwater reservoir.
• 2. Since the initiation of the project, fishery yields around Isahaya Bay have dramatically decreased. The objective of this study was to clarify the relationship between the work associated with the Isahaya Reclamation Project and the recent environmental deterioration in Ariake Bay, with references to present sediment thickness and organic matter content, and hypoxic water distributions in Isahaya Bay.
• 3. The organic matter load from the reservoir has increased since the initiation of the reclamation project and has been associated with a thick layer of fine sediment at the bottom of Isahaya Bay. The thickness of fine sediment and the total organic carbon content were higher in Isahaya Bay than in the freshwater reservoir.
• 4. Based on measurements in August 2001, hypoxic water spread widely in and around Isahaya Bay; the lowest dissolved oxygen (DO) concentration (0.53 mg L^?1) was observed just outside the dyke. An analysis based on a two‐layered box model using data obtained in August 2001 showed that the DO consumption rate in the bottom layer was high (0.61 mg O₂ L^?1 day^?1), and that 22–41% of the total organic carbon load needed to induce the hypoxic water was derived from the reclamation area.
• 5. Our findings strongly suggest that enclosed seas may suffer from eutrophic and hypoxic conditions because of their low seawater‐exchange rate. A comprehensive conservation programme and environmental assessment including physical and material transport processes in the system is needed to manage the environment of the enclosed sea.

Copyright © 2005 John Wiley & Sons, Ltd.     

Habitat use by the African anabantid fish Ctenopoma muriei: implications for costs of air breathing

Abstract –  This study examined whether habitat use by the African anabantid fish Ctenopoma muriei is consistent with predictions relating to two costs of air breathing (surface travel and aerial predation). We predicted that C. muriei would be most abundant in habitats that minimize potential costs of air breathing. We quantified environmental correlates of C. muriei abundance within a series of wetland lagoons in Uganda and found that C. muriei was more abundant in shallow waters of the deepest lagoon, in vegetated habitats, and at a depth 15–30 cm below the surface. These locations may minimize cost of travel to the surface for aerial respiration, while maintaining a reasonable distance from the surface to avoid detection by aerial predators. In addition, we experimentally tested effectiveness of vegetative cover in reducing mortality of C. muriei by aerial predators (pied kingfishers) using enclosures with and without vegetation cover in a swamp pool. We found that the presence of vegetative cover significantly reduced susceptibility of C. muriei to predation by pied kingfishers when dissolved oxygen in the water was low and air-breathing frequency was potentially high.     

Quantification of presumptive Na+/H+ antiporters of the erythrocytes of trout and eel

The presumptive Na⁺/H⁺ exchange sites of trout and eel erythrocytes were quantified using amiloride-displaceable 5-(N-methyl-N-[³H]isobutyl)-amiloride (³H-MIA) equilibrium binding to further evaluate the mechanisms of i) hypoxia-mediated modifications in the trout erythrocyte -adrenergic signal transduction system and ii) the marked differences in the catecholamine responsiveness of this system between the trout and eel. MIA was a more potent inhibitor of both trout apparent erythrocyte proton extrusion (IC₅₀ = 20.1 ± 1.1 mol l^–1, N = 6) activity (as evaluated by measuring plasma pH changes after addition of catecholamine in vitro) and specific ³H-MIA binding (IC₅₀ = 257 ± 8.2 nmol l^–1, N = 3) than amiloride, which possessed a proton extrusion IC₅₀ of 26.1 ± 1.6 mol l^–1 (N = 6) and a binding IC₅₀ of 891 ± 113 nmol l^–1 (N = 3). The specific Na⁺ channel blocker phenamil was without effect on adrenergic proton extrusion activity or specific ³H-MIA binding. Trout erythrocytes suspended in Na⁺-free saline and maintained under normoxic conditions possessed 37,675 ± 6,678 (N = 6) amiloride-displaceable ³H-MIA binding sites per cell (B_max, presumptive Na⁺/H⁺ antiporters) with an apparent dissociation constant (K_D) of 244 ± 29 nmol l^–1 (N = 6). Acute hypoxia (PO₂ = 1.2 kPa; 30 min) did not affect the K_D, yet resulted in a 65% increase in the number of presumptive Na⁺/H⁺ antiporters. Normoxic eel erythrocytes, similarly suspended in Na⁺-free saline, possessed only 17,133 ± 3,716 presumptive Na⁺/H⁺ antiporters (N = 6), 45% of that of trout erythrocytes, with a similar K_D (246 ± 41 nmol l^–1, N = 6). These findings suggest that inter- and intra-specific differences in the responsiveness of the teleost erythrocyte -adrenergic signal transduction system can be explained, in part, by differences in the numbers of Na⁺/H⁺ exchange sites.     

Ichthyoplankton distribution and abundance in relation to nearshore dissolved oxygen levels and other environmental variables within the Northern California Current System

Nearshore hypoxia along the coast of Oregon and Washington is a seasonal phenomenon that has generated concern among scientists studying this temperate upwelling ecosystem. These waters are affected by coastal upwelling‐induced hypoxia mainly during late summer and fall, but the effects of low oxygen levels on fish and invertebrate communities, particularly during the early‐life history stages, are poorly known. We investigated the effects of hypoxia and other variables on the species composition, density, vertical and horizontal distribution of fish larvae along the Oregon and Washington coasts during the summers of 2008, 2009 and 2010. Bottom‐dissolved oxygen (DO) values ranged from 0.49 to 4.79 mL L^?1, but the overall water column DO values were only moderately hypoxic during the 3 yr of sampling compared with recent extreme years. In this study, DO was found to be an environmental parameter affecting the species composition, but other variables such as season, year and depth of capture were also important. Although the overall density of fish larvae increased with increasing bottom‐DO values, the effect on individual species density was limited. Slender sole (Lyopsetta exilis) and sand sole (Psettichthys melanostictus) were the only species to have a weak trend of density with DO, but both showed negative relationships and neither relationship was significant. Our results indicate that larval fish spatial distribution was only moderately affected within the range of observed oxygen values, but low DO may be an important factor under intense hypoxic conditions.     

低氧胁迫对河川沙塘鳢抗氧化酶及ATP酶活性的影响

研究了在急性低氧1.5 h、5 h和慢性低氧3 d下,河川沙塘鳢(Odontobutis potamophila)5种组织(心、脑、肝、鳃和肾)的超氧化物歧化酶(SOD)、过氧化氢酶(CAT)及谷胱甘肽过氧化物酶(GPX)3种抗氧化酶和ATP酶活性的变化规律。结果显示:在急性低氧暴露1.5 h时,河川沙塘鳢SOD和GPX的活力在各组织中与对照组相比均无显著差异,CAT活力在心、鳃和肝3种组织呈现显著升高(P0.05),ATP酶活力在心和肝组织极显著升高(P0.01);在急性低氧暴露5 h时,除肝组织SOD酶活性显著降低外(P0.05),其它4种组织的CAT、GPX和ATP酶均不同程度显著升高(P0.05);在慢性低氧处理3 d时,心、脑组织的抗氧化酶已基本恢复至与对照组无显著差异的水平,但鳃、肝和肾中酶活力仍较高(P0.05)。研究表明,河川沙塘鳢能通过自身调节抗氧化酶及ATP酶活性,改变代谢底物,提高机体适应低氧环境的能力。     

γ-氨基丁酸对低氧胁迫下甜瓜幼苗抗氧化酶活性及表达的影响

采用营养液水培方法,研究低氧胁迫下外源GABA对甜瓜幼苗抗氧化酶（SOD、POD、CAT和APX）活性和同工酶表达的影响,采用实时荧光定量PCR方法检测幼苗根系抗氧化酶的基因表达特性。结果表明,低氧胁迫处理下,幼苗根系和叶片抗氧化酶活性和同工酶表达均高于对照,且根系CmSOD、CmPOD1、CmPOD2、CmCAT、CmAPX基因均上调表达;低氧胁迫下外源GABA处理显著提高幼苗根系和叶片SOD、CAT和APX活性以及同工酶表达,且根系CmSOD、CmCAT、CmAPX基因相对表达量在0.5~1 d迅速提高并达到最大值,且增加幅度高于低氧胁迫处理。由此可知,GABA通过促进根系抗氧化酶基因快速大量表达,提高抗氧化酶活性和同工酶的表达量,从而缓解低氧胁迫对甜瓜幼苗的伤害。     

棕点石斑鱼(♀)×蓝身大斑石斑鱼(♂)杂交后代与棕点石斑鱼低氧耐受能力初步研究

为了研究棕点石斑鱼(Epinephelus fuscoguttatus,♀)与蓝身大斑石斑鱼(E.tukula,♂)杂交后代(简称金虎石斑鱼)和棕点石斑鱼的低氧耐受能力,采用封闭式呼吸室测定棕点石斑鱼和金虎石斑鱼幼鱼的耗氧率与窒息点,在正常溶氧[(5.71±0.31)mg/L]和溶解氧下降至4.0 mg/L、3.0mg...