Projecting future habitat quality of three midwestern reservoir fishes under warming conditions

Rising temperatures caused by climate change are likely to affect cool‐water and warm‐water fishes differently. Yet, forecasts of anticipated temperature effects on fishes of different thermal guilds are lacking, especially in freshwater ecosystems. Towards this end, we used spatially explicit, growth rate potential (GRP) models to project changes in seasonal habitat quality for a warm‐water piscivore (largemouth bass Micropterus salmoides), a cool‐water piscivore (walleye Sander vitreus) and a hybrid piscivore (saugeye S. vitreus × S. canadensis) in two Midwestern reservoirs. We assessed habitat quality for two periods (early and middle 21st century) under two realistic greenhouse gas emission scenarios (a mid‐century emissions peak and a rapid continuous increase in emissions). Largemouth bass were projected to experience enhanced or slightly reduced habitat during all seasons, and throughout the mid‐21st century. By contrast, walleye habitat was projected to decline with anticipated warming, except during the spring in the smaller of our two study reservoirs and during the fall in the larger of our two study reservoirs. Saugeye habitat was projected to either increase modestly or decline slightly during the spring and fall and declines in habitat quality and quantity that were smaller than those for walleye were identified during summer. Collectively, our findings indicate that climate warming will differentially alter habitat suitability for reservoir piscivores, favouring warm‐water species over cool‐water species. We expect these changes in habitat quality to impact the dynamics of reservoir fish populations to varying degrees necessitating the consideration of climate when making future management decisions.     

Inhibiting fungus on largemouth bass eggs with copper sulfate and its toxicity to fry and juveniles

This study determined the effectiveness of copper sulfate (CuSO₄) to inhibit fungal growth (caused by Saprolegnia spp.) on largemouth bass (LMB) eggs spawned on/in fiber mats in very high-alkalinity/-hardness waters; experiments also determined the toxicity of CuSO₄ to LMB fry and juveniles. An untreated control and three CuSO₄ concentrations (10, 20, and 40 mg/L) were tested under a flow-through scenario in the effectiveness experiment. Eggs were treated daily until hatching began. Fungal load at the time of hatch had a total area > 3.0 cm² in the untreated controls, total area 1.0 to <2.0 cm² in the 10 and 20 mg/L CuSO₄ treatments, and total area > 1.0 cm² in the 40 mg/L CuSO₄ treatments. Fungus samples were identified as Saprolegnia australis. The 24-hr median lethal concentration (LC50) values on the LMB yolk-sac and swim-up fry were 32.0 and 4.6 mg/L CuSO₄, respectively; the No Observed Effect Concentrations (NOEC) were 16.0 and 0.125 mg/L CuSO₄, respectively. Juvenile LMB were extremely tolerant to CuSO₄, and their 24-hr LC50 value was 185.5 mg/L; the NOEC was 64 mg/L. This study indicates that CuSO₄ can be an important resource for hatcheries to control egg fungus, especially in high-alkalinity/-hardness waters.     

条纹石鮨摄食强度与代谢及能量收支间的关系

设日摄食率为０．４％、１．５％、４．０％三种水平,分别测定条纹石鱼旨Ｍｏｒｏｎｅｓａｘａｔｉｌｉｓ幼鱼的代谢及能量的收支情况。处于饱食（日摄食率４．０％）及维持状态（日摄食率１．５％）下,该鱼代谢率增加的峰值分别于摄食后３ｈ及７ｈ内出现,为静止时代谢水平的２．１０倍和２．４６倍,ＳＤＡ（特殊动力作用）持续时间均为２１ｈ,ＳＤＡ总耗能量分别占摄入能的１３％和３５．８％。条纹石鱼旨在饱食时的转化效率Ｋ（湿重）为２０．８５％。三种摄食水平下条纹石鱼旨的能量收支方程分别为：饱食状态（日摄食率４．０％）时,１００Ｃ＝８．４Ｆ＋７．８Ｕ＋１３．０ＳＤＡ＋３６．９（Ｒｓ＋Ｒａ）＋３３．９Ｇ;维持状态（日摄食率１．５％）时,１００Ｃ＝７．８Ｆ＋４．１Ｕ＋３５．８ＳＤＡ＋５２．３（Ｒｓ＋Ｒａ）,其中Ｇ＝０;减重状态（日摄食率０．４％）时,（Ｆ＋Ｕ＋Ｒ）／（Ｃ＋Ｐ１）＝６７．３％,其中Ｃ＋Ｐ１＝１４．４Ｃ＋８５．６Ｐ１,Ｆ＋Ｕ＋Ｒ＝１．８Ｆ＋８．１Ｕ＋５７．４Ｒ。     

Efficacy of phytase on phosphorus utilization in practical diets fed to striped bass Morone saxatilis

Several experiments were conducted to determine the effects of phytase on dietary phosphorus (P) utilization by striped bass Morone saxatilis fed high phytate diets. The experiments were designed to determine the effectiveness of various dietary levels of a dry or liquid phytase concentrate incorporated in diets to improve the P utilization of striped bass. Fish were fed various basal diets containing over 700 g kg^?1 plant feed ingredients and 4.9–7.1 g kg^?1 P and 1.5–1.7 g kg^?1 non-phytin P. A diet supplemented with potassium monophosphate (PMP) and containing 9 g kg^?1 total P and 6 g kg^?1 non-phytin P with no added phytase was the positive control. The dietary treatments were assigned to duplicate tanks and diets were fed to juvenile striped bass for up to 14 weeks. The effectiveness of the phytase treatments was determined by measuring weight gain, feed conversion, serum, scale and vertebral calcium and P, as well as P absorption. Apparent P absorption was determined using 5 g kg^?1 chromic oxide as an indigestible marker in the diet. In experiment one, significant improvements (P < 0.05) were found in scale and vertebral phosphorus concentrations with 2400 Phytase Units (PU) kg^?1 (PU is the quantity of enzyme which liberates one micromole of inorganic P per minute from 0.015 tool L^?1 sodium phytate at 37°C and pH 5.5) added to the diet. In experiment two, significant differences were observed between serum phosphorus in the phytase and no-phytase groups, while there were no differences between the positive control (PMP supplemented) and the phytase-treated fish. It was concluded that 2400 PU kg^?1 of enzyme resulted in bone mineralization and serum phosphorus concentrations equal to that observed with 13 g kg^?1 dietary PMP addition (9 g kg^?1 total P).     

Turbidity‐induced changes in emergent effects of multiple predators with different foraging strategies

Abstract – In natural systems, prey frequently interact with multiple predators and the outcome often cannot be predicted by summing the effects of individual predator species. Multiple predator interactions can create emergent effects for prey, but how those change across environmental gradients is poorly understood. Turbidity is an environmental factor in aquatic systems that may influence multiple predator effects on prey. Interactions between a cruising predator (largemouth bass Micropterus salmoides) and an ambush predator (muskellunge Esox masquinongy) and their combination foraging on a shared prey (bluegill Lepomis macrochirus) were examined across a turbidity gradient. Turbidity modified multiple predator effects on prey. In clear water, combined predators consumed in total more prey than expected from individual predator treatments, suggesting risk enhancement for prey. In moderately turbid water, the predators consumed fewer prey together than expected, suggesting a risk reduction for prey. At high turbidity, there were no apparent emergent effects; however, the cruising predator consumed more prey than the ambush predator, suggesting an advantage for this predator. Understanding multiple predator traits across a gradient of turbidity increases our understanding of how complex natural systems function.     

Nearshore fish assemblages associated with introduced predatory fishes in lakes

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Amino acid availability from selected animal‐ and plant‐ derived feedstuffs for market‐size sunshine bass (Morone chrysops × Morone saxatilis)

A study was conducted with market‐size (867 g) hybrid striped bass to determine the nutrient digestibility and apparent amino acid availability of six common feedstuffs. The animal‐protein feedstuffs tested were menhaden fish meal (MEN), anchovy fish meal (ANCH), pet‐food grade poultry by‐product meal (PBM‐pet), and feed‐grade poultry by‐product meal (PBM‐feed), while the plant‐protein feedstuffs were dehulled solvent extracted soybean meal (SBM) and distiller’s dried grains with solubles (DDGS). Test diets consisted of a 70 : 30 mixture of reference diet to test ingredient with chromic oxide (10 g kg^?1%) as the inert marker. Diets were randomly assigned to triplicate tanks of fish that were fed their respective diets for 7 days prior to fecal collection by stripping. Two feeding trials were conducted sequentially to determine the digestibility of the six test ingredients. In trial 1, the three ingredients evaluated were MEN, PBM‐feed, and PBM‐pet. In trial 2, the three ingredients evaluated were ANCH, SBM, and DDGS. Apparent digestibility coefficients of protein (ADC‐CP) were significantly (P < 0.05) different among test ingredients in trial 1 as protein digestibility of MEN (86%) was significantly higher (P < 0.05) than that of PBM‐feed (75%), but was not significantly different from that of PBM‐pet (78%). Protein digestibilities in trial 2 were not significantly different among test ingredients and averaged 76% for ANCH, SBM, and DDGS. Some apparent amino acid availability coefficients differed among feedstuffs for both trial 1 and trial 2. MEN provided higher amino acid availabilities for alanine, aspartic acid, glutamic acid, lysine, valine, and tryptophan (99%, 98%, 94%, 96%, 99%, and 108%, respectively) when compared to PBM‐feed (73%, 50%, 69%, 80%, 77%, and 91%, respectively) and PBM‐pet (79%, 66%, 81%, 81%, 78%, and 99% respectively). Glycine, histidine, leucine, and proline availabilities in MEN (95%, 96%, 100%, and 98%, respectively) were significantly (P < 0.05) higher than those of PBM‐feed (64%, 82%, 82%, and 57%, respectively), but were not significantly different from PBM‐pet (85%, 92%, 89%, and 80%, respectively). For trial 2, apparent amino acid availabilities for cystine, isoleucine, lysine, and tyrosine were significantly higher (P < 0.05) among treatments fed SBM (100%, 87%, 93%, and 97%, respectively) and ANCH (37%, 95%, 92%, and 84%, respectively) compared to treatments fed DDGS (?13%, 52%, 62% and 62%, respectively). Overall, amino acid availability in SBM and the two PBM’s appear comparable to MEN and ANCH and corroborate their high value as potential replacements for fish meal in sunshine bass diets. However, DDGS provided the lowest availabilities for several amino acids and should be used with caution.     

Space use and inferred spawning activity of three exploited gamefish species on a large artificial reef

Intense fishing pressure has led to changes in species composition, demography and the over‐exploitation of many coastal fishes. To restore populations, artificial reefs (ARs) are used with the assumption that new habitat will increase fish productivity. Kelp bass (Paralabrax clathratus), barred sand bass (P. nebulifer) and California sheephead (Semicossyphus pulcher) are three important recreational gamefish species in southern California. Home ranging behaviour, space use and spawning‐related activity of these three species were quantified on a large AR. Kelp bass used the largest amount of area, but space use was similar among species. While no spawning behaviour could be determined for sheephead, kelp bass exhibited two different activity patterns during spawning months and barred sand bass migrated (indicative of spawning). Results of this study indicate that this large AR is providing suitable habitat for these species, and spawning‐related activity could be a sign that this AR is meeting essential life history demands.     

Isolation and identification of a viral haemorrhagic septicaemia virus (VHSV) isolate from wild largemouth bass Micropterus salmoides in China

Fish rhabdoviruses are a family of viruses responsible for large‐scale fish die‐offs worldwide. Here, we reported the isolation and identification of a member of rhabdoviruses from wild largemouth bass (Micropterus salmoides) in the coastal area of the Pearl River Estuary, China. This virus isolate was identified as viral haemorrhagic septicaemia virus (VHSV) by specific RT‐PCR. Furthermore, the virus (VHSVLB2018) was isolated by cell culture using fathead minnow cells and confirmed by RT‐PCR. Electron microscopy showed the presence of bullet‐shaped viral particles in the cytoplasm of infected cells. The complete sequencing of VHSVLB2018 confirmed that it was genome configuration typical of rhabdoviruses. Phylogenetic analysis based on whole‐genome sequences and G gene nucleotides sequences revealed that VHSVLB2018 was assigned to VHSV genogroup Ⅳa. The pathogenicity of VHSVLB2018 was determined in infection experiments using specific pathogen‐free largemouth bass juveniles. VHSVLB2018‐infected fish showed typical clinical signs of VHSV disease, including darkened skin, petechial haemorrhages and pale enlarged livers, with the cumulative mortalities reached 63.3%–93.3% by 7 days post‐infection. VHSVLB2018 was re‐isolated from dead fish and confirmed by RT‐PCR. Together, this is the first report of isolation and identification of a VHSV isolate from wild largemouth bass in China.     

Experimental oral transmission of largemouth bass virus

Largemouth bass virus (LMBV) is a recently discovered iridovirus that causes a fatal disease of largemouth bass, Micropterus salmoides (Lacepède). Fish can become infected by waterborne LMBV, but oral transmission of this virus has not been demonstrated previously. Largemouth bass were gavaged with guppies, Poecilia reticulata Peters, which had been injected with LMBV, and then sampled periodically during a 7‐week observation period. The dose of LMBV averaged 10^5.6 tissue culture infectious doses – 50% cytopathic endpoint (TCID₅₀) per largemouth bass. Five of 24 largemouth bass exposed to LMBV became infected with the virus, but none of the fish had clinical signs typical of LMBV disease. Virus titres in largemouth bass were highest in swim bladder (10^5.5–9.5 TCID₅₀ g^?1) and were 10^5.2 TCID₅₀ g^?1 or lower in cutaneous mucus, head kidney, trunk kidney, spleen, gonad and intestine. These results indicate that LMBV can be transmitted orally to largemouth bass, but further study is needed to determine the factors affecting pathogenicity of the virus.