Do the effects of piscivorous largemouth bass cascade to the plankton?

Ecologists have hypothesized that an increase in the biomass of piscivorous fish in lakes will cause a decrease in populations of planktivorous fish, an increase in the size of herbivorous zooplankton and a decrease in the biomass of phytoplankton. Here we present an experimental test of whether the effects of largemouth bass (Micropterus salmoides) cascade to the planktivorous fish, zooplankton and phytoplankton of a 15-ha water storage reservoir. A pilot study indicated that the reservoir was eutrophic with dense populations of planktivorous fish dominated by threadfin shad (Dorosoma petenense). No piscovorous fish were present in the reservoir. We conducted a one-month mesocosm experiment using water and plankton from the reservoir showing that the presence of threadfin shad reduced large-sized zooplankton and increased the productivity and biomass of phytoplankton. To test whether the effects of piscivorous fish could cascade to the plankton, we assessed the effects of the addition of piscivorous largemouth bass on the planktivorous fish, zooplankton and biomass of phytoplankton of the reservoir by monitoring the reservoir during the year before and the two years after largemouth bass were stocked. In the second year after the addition of largemouth bass, the number of planktivorous fish decreased and the relative abundance of threadfin shad declined. Although the abundance of cladocerans increased after the addition of largemouth bass, the average size of zooplankton did not change. We did not detect changes in chlorophyll a, Secchi depth, or concentrations of total phosphorus and total nitrogen as a result of the addition of largemouth bass.     

Using an integrative research approach to improve fish migrations in regulated rivers: a case study on Pacific Salmon in the Seton River,Canada

Hydrobiologia - Many of the world’s rivers are dammed, altering the physiology, behaviour, ecology and survival of fish. Integrative research has the potential to improve our understanding of...     

Physiological benefits of being small in a changing world: responses of Coho salmon (Oncorhynchus kisutch) to an acute thermal challenge and a simulated capture event

Evidence is building to suggest that both chronic and acute warm temperature exposure, as well as other anthropogenic perturbations, may select for small adult fish within a species. To shed light on this phenomenon, we investigated physiological and anatomical attributes associated with size-specific responses to an acute thermal challenge and a fisheries capture simulation (exercise+air exposure) in maturing male coho salmon (Oncorhynchus kisutch). Full-size females were included for a sex-specific comparison. A size-specific response in haematology to an acute thermal challenge (from 7 to 20 °C at 3 °C h(-1)) was apparent only for plasma potassium, whereby full-size males exhibited a significant increase in comparison with smaller males ('jacks'). Full-size females exhibited an elevated blood stress response in comparison with full-size males. Metabolic recovery following exhaustive exercise at 7 °C was size-specific, with jacks regaining resting levels of metabolism at 9.3 ± 0.5 h post-exercise in comparison with 12.3 ± 0.4 h for full-size fish of both sexes. Excess post-exercise oxygen consumption scaled with body mass in male fish with an exponent of b = 1.20 ± 0.08. Jacks appeared to regain osmoregulatory homeostasis faster than full-size males, and they had higher ventilation rates at 1 h post-exercise. Peak metabolic rate during post-exercise recovery scaled with body mass with an exponent of b~1, suggesting that the slower metabolic recovery in large fish was not due to limitations in diffusive or convective oxygen transport, but that large fish simply accumulated a greater 'oxygen debt' that took longer to pay back at the size-independent peak metabolic rate of ~6 mg min(-1) kg(-1). Post-exercise recovery of plasma testosterone was faster in jacks compared with full-size males, suggesting less impairment of the maturation trajectory of smaller fish. Supporting previous studies, these findings suggest that environmental change and non-lethal fisheries interactions have the potential to select for small individuals within fish populations over time.     

Toxic gain of function from mutant FUS protein is crucial to trigger cell autonomous motor neuron loss

FUS is an RNA‐binding protein involved in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Cytoplasmic FUS‐containing aggregates are often associated with concomitant loss of nuclear FUS. Whether loss of nuclear FUS function, gain of a cytoplasmic function, or a combination of both lead to neurodegeneration remains elusive. To address this question, we generated knockin mice expressing mislocalized cytoplasmic FUS and complete FUS knockout mice. Both mouse models display similar perinatal lethality with respiratory insufficiency, reduced body weight and length, and largely similar alterations in gene expression and mRNA splicing patterns, indicating that mislocalized FUS results in loss of its normal function. However, FUS knockin mice, but not FUS knockout mice, display reduced motor neuron numbers at birth, associated with enhanced motor neuron apoptosis, which can be rescued by cell‐specific CRE‐mediated expression of wild‐type FUS within motor neurons. Together, our findings indicate that cytoplasmic FUS mislocalization not only leads to nuclear loss of function, but also triggers motor neuron death through a toxic gain of function within motor neurons.     

Feeding behavior of the cichlid,Sarotherodon galilaeum: selective predation on Lake Kinneret zooplankton

In laboratory feeding trials, we analyzed the feeding behavior and selectivity of the cichlid, Sarotherodon galilaeum, for zooplankton prey from Lake Kinneret, Israel. The feeding behavior was dependent on fish size. Fish less than 20 mm SL fed on zooplankton as obligate particulate feeders. Fish from 20 to 42 mm SL fed either as particulate feeders or as filter feeders. Fish larger than 62 mm SL fed as obligate filter feeders. Particulate-feeding fish were size selective and had highest feeding electivities for large-sized zooplankton species. Filter-feeding fish had highest feeding electivities for zooplankton species with poor escape ability. In general, S. galilaeum predation pressure would be greatest on Ceriodaphnia reticulata, a large-bodied and easily captured species which is selected by both particulate-feeding and filter-feeding fish.     

Context-dependent effects of bluegill in experimental mesocosm communities

Most knowledge of direct and indirect effects of zooplanktivorous fish has come from studies in which a treatment with a zooplanktivore is compared to a fishless control. However, effects of a zooplanktivore may be different in the presence of other fish species because the other fish have direct and indirect effects that may alter the effects of the zooplanktivore in question. To test this hypothesis, we conducted a tank mesocosm experiment of 2×2 factorial design in which the presence and absence of bluegill (Lepomis macrochirus) were cross-classified with the presence and absence of a fish assemblage composed of western mosquitofish (Gambusia affinis) and common carp (Cyprinus carpio). The presence of bluegill decreased Daphnia, Ceriodaphnia, cyclopoid copepodids, calanoid copepodids, copepod nauplii, amphipods, gastropods, and notonectids. Daphnia, Ceriodaphnia, cyclopoid copepodids, copepod nauplii, gastropods, notonectids, Najas, and Chara were decreased and herbivorous rotifers, turbidity, chlorophyll a, total nitrogen and total phosphorus were increased in the presence of the fish assemblage. Significant bluegill×fish assemblage interaction effects were detected for Daphnia, Ceriodaphnia, cyclopoid copepodids, copepod nauplii, gastropods, and notonectids. Analysis of simple effects for these response variables revealed that all significant bluegill effects in the absence of the fish assemblage were not significant in the presence of the fish assemblage. Our results indicate that the effects of bluegill may be context dependent, or dependent upon the presence of other trophically similar fish species. Received: 3 November 1998 / Accepted: 24 September 1999     

Lake trophic state and the limnological effects of omnivorous fish

Ecologists have hypothesized that planktivorous fish have greater effects on the plankton and water quality of oligotrophic lakes than eutrophic lakes. We tested this hypothesis in a tank-mesocosm experiment of factorial design in which five biomass levels of filter-feeding omnivorous gizzard shad (Dorosoma cepedianum) were cross-classified with two levels of lake trophic state achieved by filling tank-mesocosms with water and plankton transported by truck from two lakes with different trophic states. The presence of gizzard shad significantly increased total phosphorus, primary productivity, chlorophyll, and particulate phosphorus (PP) 2–20 and 20–200 μm and significantly decreased Secchi depth, cladocerans, copepods and PP > 200 μm. The effects of gizzard shad on chlorophyll, Secchi depth, cladocerans, copepods and PP 2–20 and > 200 μm were dependent on lake trophic state and most intense in the eutrophic lake system. This experiment suggests that filter-feeding omnivorous fish interact synergistically with trophic state so that the limnological effects of omnivorous fish become more intense with increased eutrophication.     

Responses of a eutrophic pond community to separate and combined effects of N:P supply and planktivorous fish: a mesocosm experiment

We conducted an outdoor mesocosm experiment of factorial design consisting of three levels of nutrient supply (no nutrient addition and additions of nitrogen and phosphorus in ratios of 10:1 and 45:1) cross-classified with two levels of bluegill (Lepomis macrochirus) (presence and absence). Nutrient supply significantly affected total phosphorus (TP), total nitrogen (TN), TN: TP ratio, turbidity, Secchi depth, phytoplankton chlorophyll, filamentous blue-green algae, periphyton chlorophyll, Asplanchna and non-predatory rotifers. The presence of bluegill significantly increased TP, turbidity, diatoms, unicellular green algae, colonial blue-green algae, filamentous blue-green algae, periphyton chlorophyll, Asplanchna and non-predatory rotifers, and decreased Secchi depth, cladocerans, cyclopoid copepodids, copepod nauplii and chironomid tube densities. Nutrient supply and fish effects were not independent of each other as shown by significant nutrient × fish interaction effects for TP, Secchi depth, filamentous blue-green algae, periphyton chlorophyll, Asplanchna and non-predatory rotifers.     

The efficacy of field techniques for obtaining and storing blood samples from fishes

Prompted by the dramatic increase in the use of blood analyses in fisheries research and monitoring, this study investigated the efficacy of common field techniques for sampling and storing blood from fishes. Three questions were addressed: (1) Do blood samples taken via rapid caudal puncture (the ‘grab‐and‐stab’ technique) yield similar results for live v. sacrificed groups of fishes? (2) Do rapidly obtained caudal blood samples accurately represent blood properties of fishes prior to capture? (3) Does storage of whole blood in an ice slurry for a working day (8·5 h) modify the properties of the plasma? It was shown that haematocrit, plasma ions, metabolites, stress hormones and sex hormones of caudal blood samples were statistically similar when taken from live v. recently sacrificed groups of adult coho salmon Oncorhynchus kisutch. Moreover, this study confirmed by using paired blood samples from cannulated O. kisutch that blood acquired through the caudal puncture technique (mean ±s.e . 142 ± 26 s after capture) was representative of fish prior to capture. Long‐term (8·5 h) cold storage of sockeye salmon Oncorhynchus nerka whole blood caused significant decreases in plasma potassium and chloride, and a significant increase in plasma glucose. Previous research has suggested that these changes largely result from net movements of ions and molecules between the plasma and erythrocytes, movements that can occur within minutes of storage. Thus, blood samples from fishes should be centrifuged as quickly as practicable in the field for separation of plasma and erythrocytes to prevent potentially misleading data.     

Biomass-dependent effects of common carp on water quality in shallow ponds

We examined the biomass-dependent effects of common carp (Cyprinus carpio) on water quality in 10 ponds at the Eagle Mountain Fish Hatchery, Fort Worth, Texas, USA. Ponds contained 0–465 kg ha⁻¹ of common carp. We measured limnological variables at weekly intervals for four weeks in early summer, after which ponds were drained and the biomass of fish and macrophytes was determined. Common carp biomass was significantly positively correlated with chlorophyll a, total phosphorus, total nitrogen, and Keratella spp. density and negatively correlated to bushy pondweed (Najas guadalupensis) biomass. In addition, we combined our data with data from comparable studies to develop more robust regression models that predict the biomass-dependent effects of common carp on water quality variables across a wide range of systems.