Population ecology and prey consumption by fathead minnows in prairie wetlands: importance of detritus and larval fish

Abstract –  The fathead minnow Pimephales promelas occurs in high densities in wetlands of the prairie pothole region (PPR) of North America, but food resources sustaining these populations are poorly known. We assessed population dynamics and prey consumption of fathead minnow populations in three PPR wetlands for 2 years. Fish density peaked at 107 fish per m² for all age classes combined. Larval and juvenile fish dominated these populations in terms of abundance and accounted for 83% of total prey consumption. Detritus dominated fish diets, representing 53%, 40% and 79% of diet mass for larval, juvenile and adult fish respectively. Detritus consumption was positively related to minnow density and negatively related to invertebrate abundance, but only for adult fish. Seasonal production:biomass ratios were unrelated to proportions of detritus in the diet for all ages of fish, indicating that detritus is an important food resource capable of meeting metabolic demands and sustaining fish growth in high-density populations. Detritus consumption may also weaken links between abundance of invertebrate prey and minnows, promoting dense fish populations with strong, consistent influences on wetland ecosystems.     

Fathead minnow reproduction: Implications for commercial culture

The fathead minnow, Pimephales promelas, is widely used as a bait, forage, and research fish in the United States. A hardy and fecund fish, this species has many attributes that are excellent for culture. Unfortunately, despite the widespread use of fathead minnows in toxicity testing and thousands of resulting publications, relatively little aquaculture‐related research has been conducted in support of commercial production. On the surface, current commercial fathead minnow production practices appear much the same as those of a decade ago. However, producers continue to refine culture methods, balancing broodfish stocking rates, spawning substrate quantity, and feeding rates in an attempt to meet both losses to predators and market demand. This review examines relevant reproduction‐related studies in the fields of ecology, behavior, toxicology, and aquaculture with the goal of advancing fathead minnow culture. In fathead minnow production, relative to the culture of food fish species, reproduction is vital, more so than rapid growth or a low feed conversion ratio. Fish numbers may exceed 1 million fish/ha, while feeding rates are relatively low and in feeder fish production, growth is deliberately restrained in order to maintain fish within market sizes year‐round. Underappreciated factors identified as affecting reproduction and with implications for commercial culture include: (a) poor egg adhesion to commonly used spawning substrates, (b) egg and fry cannibalism at high fish densities, and (c) the relatively short breeding period of individual males. Results highlight the importance of selecting an appropriate broodfish stocking rate based on fish size, anticipated pond fertility, and feeding program. New methods to improve reproductive performance will likely increase costs and will need to be accompanied by thorough economic analyses.     

Early- to late-summer population growth and prey consumption by age-0 pollock (Theragra chalcogramma), in two years of contrasting pollock abundance near the Pribilof Islands, Bering Sea

Acoustic survey data were used to estimate the abundance and distribution of age-0 walleye pollock and zooplankton near the Pribilof Islands, Bering Sea, nursery area at two time periods in two consecutive years: the beginning of August, and mid-September, of 1996 and 1997. The 1996 pollock year class ultimately produced a large adult cohort in the eastern Bering Sea, while the 1997 year class produced a below-average adult cohort. Acoustic densities of age-0 pollock were significantly lower in August – and declined more strongly from August to September – in 1997 than in 1996, indicating that the trend to adult cohort strength was already set by August. Diet composition analyses revealed that age-0 pollock ate a much higher proportion of euphausiids in 1997 than in 1996, despite lower acoustic abundance of euphausiids in 1997. We infer that in 1996, age-0 pollock experienced greater feeding success by August, with high concentrations of copepods available for smaller fish to consume, and high concentrations of euphausiids available for larger individuals. In 1997, age-0 pollock had lower body condition in August and may have been limited by the availability of small (<2 mm) copepods. Bioenergetic modeling of prey consumption did not indicate a likelihood that age-0 pollock would begin to deplete euphausiids until late August in 1996, and not at all between August and mid-September in 1997.     

Diet dynamics of the juvenile piscivorous fish community in Spirit Lake, Iowa, USA, 1997–1998

Abstract – We assessed temporal dynamics and variation among species and age-classes in the diets of age 0 and age 1 piscivorous fish species in Spirit Lake, Iowa, USA during 1997 and 1998. Species included walleye Stizostedion vitreum , yellow perch Perca flavescens , smallmouth bass Micropterus dolomieui , largemouth bass Micropterus salmoides , black crappie Pomoxis nigromaculatus and white bass Morone chrysops. Thirty taxa were identified in diets, including 12 species of fish. We found dramatic differences in diets among species, among age-classes within species and over time. Walleye, largemouth bass, smallmouth bass and white bass were piscivorous at age 0. Black crappie began piscivory at age 1. Yellow perch also began piscivory at age 1, but fish were a very small fraction of age-1 diets. The primary temporal pattern, seen in several species and age-classes, was an increase in piscivory from spring to fall. This pattern was due to the lack of small, age-0 prey fish in spring. Although some patterns were evident, the taxonomic composition of the diets of all species was highly variable over time, making generalizations difficult. A surprising result was the absence of yellow perch in the diet of age-0 walleye, despite their abundance in Spirit Lake and prominence in diets of age-1 walleye and other age 1-piscivores. Age-0 yellow perch were consistently too large to be eaten by age-0 piscivores, which preyed primarily on invertebrates and smaller fish such as johnny darters Etheostoma nigrum and age 0 bluegill Lepomis macrochirus. This finding suggests that predator-prey interactions and resulting population dynamics may be quite different in Spirit Lake than in other systems dominated by walleye and yellow perch.     

Shift happens: Evaluating the ability of autumn stocked walleye Sander vitreus to shift to natural prey

Hatchery propagation techniques, such as pellet-rearing, can result in altered feeding behaviour. Walleye Sander vitreus (Mitchill) is a commonly propagated sportfish, yet little is known regarding its ability to switch to live prey post-stocking. The objectives were to evaluate temporal changes in diet composition and condition as well as evaluate the relationship between total length and presence of different prey consumed by stocked walleye fry and fingerlings. Fingerling walleye had higher average proportions of empty stomachs and benthic invertebrates but less fish that stocked walleye fry. The presence of zooplankton, benthic invertebrates or fish was not related to walleye length. Walleye condition was similar between cohorts and did not change over days post-stocking. Percent similarity index values between cohorts were variable (0.0 to 67.9%). It was concluded that stocked walleye fingerlings consume lower quality prey items than stocked fry counterparts at least up to 49-day post-stocking, which may have implications for post-stocking survival.     

Complex influences of low-head dams and artificial wetlands on fishes in a Colorado River tributary system

Abstract  Low-head dams in arid regions restrict fish movement and create novel habitats that have complex effects on fish assemblages. The influence of low-head dams and artificial wetlands on fishes in Muddy Creek, a tributary of the Colorado River system in the USA was examined. Upstream, fish assemblages were dominated by native species including two species of conservation concern, bluehead sucker, Catostomus discobolus Cope, and roundtail chub, Gila robusta Baird and Girard. The artificial wetlands contained almost exclusively non-native fathead minnow, Pimephales promelas Rafinesque, and white sucker, Catostomus commersonii (Lacepède). Downstream, fish assemblages were dominated by non-native species. Upstream spawning migrations by non-native white suckers were blocked by dams associated with the wetlands. However, the wetlands do not provide habitat for native fishes and likely inhibit fish movement. The wetlands appear to be a source habitat for non-native fishes and a sink habitat for native fishes. Two non-native species, sand shiner, Notropis stramineus (Cope), and redside shiner, Richardsonius balteatus (Richardson), were present only downstream of the wetlands, suggesting a beneficial role of the wetlands in preventing upstream colonisation by non-native fishes.     

Integrating seabird dietary and groundfish stock assessment data: Can puffins predict pollock spawning stock biomass in the North Pacific?

Information on the annual variability in abundance and growth of juvenile groundfish can be useful for predicting fisheries stocks, but is often poorly known owing to difficulties in sampling fish in their first year of life. In the Western Gulf of Alaska (WGoA) and Eastern Bering Sea (EBS) ecosystems, three species of puffin (tufted and horned puffin, Fratercula cirrhata, Fratercula corniculata, and rhinoceros auklet, Cerorhinca monocerata, Alcidae), regularly prey upon (i.e., “sample”) age-0 groundfish, including walleye pollock (Gadus chalcogramma, Gadidae) and Pacific cod (Gadus microcephalus, Gadidae). Here, we test the hypothesis that integrating puffin dietary data with walleye pollock stock assessment data provides information useful for fisheries management, including indices of interannual variation in age-0 abundance and growth. To test this hypothesis, we conducted cross-correlation and regression analyses of puffin-based indices and spawning stock biomass (SSB) for the WGoA and EBS walleye pollock stocks. For the WGoA, SSB leads the abundance of age-0 fish in the puffin diet, indicating that puffins sample the downstream production of the WGoA spawning stock. By contrast, the abundance and growth of age-0 fish sampled by puffins lead SSB for the EBS stock by 1–3 years, indicating that the puffin diet proxies incoming year class strength for this stock. Our study indicates connectivity between the WGoA and EBS walleye pollock stocks. Integration of non-traditional data sources, such as seabird diet data, with stock assessment data appears useful to inform information gaps important for managing US fisheries in the North Pacific.     

Whole-body amino acid composition and comparative aspects of amino acid nutrition of the goldfish, golden shiner and fathead minnow

Pond-raised fingerling goldfish (Carassius auratus), golden shiners (Notemigonus crysoleucas) and fathead minnows (Pimephales promelas) were analyzed for whole-body amino acid composition. All three species had similar amino acid patterns in whole-body tissue. These compositional data were also used to compute essential amino acid ratios (A/E ratios) which were compared with the quantified amino acid requirements of another cyprinid species, the common carp (Cyprinus carpio). The whole-body A/E ratios of the three baitfish species were very similar to the A/E ratios of the carp requirement values. Since previous studies have established a high correlation between whole-body amino acid patterns and dietary amino acid requirement patterns of several fish species, the whole-body amino acid values determined in this study will provide indices for formulating diets for the goldfish, golden shiner and fathead minnow.     

Impact of Copper Sulfate on Plankton in Channel Catfish Nursery Ponds

Many fish culturists are interested in applying copper sulfate pentahydrate (CSP) to channel catfish, Ictalurus punctatus, nursery ponds as a prophylactic treatment for trematode infection and proliferative gill disease by killing snails and Dero sp., respectively, before stocking fry. However, copper is an algaecide and may adversely affect phytoplankton and zooplankton populations. We evaluated the effects of prophylactic use of copper sulfate in catfish nursery ponds on water quality and phytoplankton and zooplankton populations. In 2006, treatments of 0 mg/L CSP, 3 mg/L CSP (0.77 mg/L Cu), and 6 mg/L CSP (1.54 mg/L Cu) were randomly assigned to 0.04‐ha ponds. In 2007, only treatments of 0 and 3 mg/L CSP were randomly assigned to the 16 ponds. Ponds treated with CSP had significantly higher pH and significantly lower total ammonia concentrations. Treatment of both CSP rates increased total algal concentrations but reduced desirable zooplankton groups for catfish culture. CSP has been shown to be effective in reducing snail populations at the rate used in this study. CSP treatment also appears to be beneficial to the algal bloom, shifting the algal population to green algae and increasing total algal biomass within 1 wk after CSP treatment. Although zooplankton populations were adversely affected, populations of important zooplankton to catfish fry began rebounding 6–12 d after CSP treatment. Therefore, if CSP is used to treat catfish fry ponds of similar water composition used in this study, fry should not be stocked for about 2 wk after CSP application to allow time for the desirable zooplankton densities to begin increasing.     

Mycoplasma contamination in fish cell lines: an evaluation of detection by differential incorporation of 3H-uridine and 14C-uracil

Abstract. Differential incorporation of uridine and uracil was used to assay for mycoplasma contamination in five fish cell lines: bluegill fry (BF-2), chinook salmon embryo (CHSE-214), epithelioma papillosum cyprini (EPC), fathead minnow (FHM) and rainbow trout gonad (RTG-2). The method was not suitable for monitoring BF-2, CHSE-214, FHM, and RTG-2 cell lines because they incorporated uracil. Differential incorporation of uridine and uracil may be applicable for screening EPC cells because only this cell line could distinguish cultures experimentally infected with Mycoplasma orale from cultures known to be free from microbial contaminants.     

Effects of reproductive timing and hatch date on fathead minnow recruitment

Abstract –  Timing of reproduction can be an important determinant of recruitment success for fish in strongly seasonal environments, both for individuals hatching at different times over extended spawning seasons and for entire cohorts, if the spawning period is accelerated or delayed among years. To examine potential demographic consequences of delayed spawning, we staggered dates that fathead minnow ( Pimephales promelas ) were introduced into experimental ponds in Alberta, Canada, by 3 weeks and compared growth and survival of offspring from early- and late-stocked fish. By autumn, size and mass were consistently greater in early-hatched minnows, regardless of cohort density. Size differences between treatments persisted through the second summer, which likely contributed to a higher proportion of early-hatched fish reaching sexual maturity as yearlings compared with late-hatched counterparts. Because late spawning can limit growth and subsequent maturation of progeny, temporal variability in reproductive timing should be considered when assessing recruitment potential of new year-classes.     

Alarm substances elicit limited population‐level responses in fathead minnow

Abstract – Alarm substances, chemical cues released by injured prey, are associated with increased predation risk. In the laboratory, fathead minnows limit conspicuous behaviours, such as foraging and nest guarding, when exposed to these cues. Although such responses could lead to reductions in growth and reproduction, with subsequent demographic consequences (e.g., recruitment), effects of alarm substances at the population level are largely unknown. In three field experiments, ponds and cattle troughs stocked with fathead minnow populations were treated with alarm substances or a water control over the summer breeding and growing season. Alarm substances had no effect on male parental behaviour. In one experiment, spawning occurred earlier with exposure to alarm substances; however, there was no subsequent effect on recruitment of young in this or in the other two experiments. Despite individual‐level effects in short‐term experiments, repeated exposure to alarm substances over a season had no measureable impact at the population scale.     

A review of the distribution, ecology and population dynamics of age-0 walleye pollock in the Gulf of Alaska

This review paper synthesizes published research and unpublished data on the abundance and distribution patterns, ecology and population dynamics of walleye pollock ( Theragra chalcogramma ) during their first year of life (age-0) in the Gulf of Alaska. Distribution patterns have been described using mainly trawl catches, but recently, acoustic methodology has been employed, especially in examining vertical distributions. Although age-0 pollock are found throughout the Gulf, the highest catches occurred west of Kodiak Island. Pollock are pelagic for at least their first 6 months of life but show an ontogenetic increase in depth distribution superimposed on a pronounced diel vertical migration at a larger size. Daily growth rates are variable depending on year, season and area, and growth generally ceases during the winter. The diet of age-0 pollock shifts from mainly copepods in early juveniles to euphausiids by fall, with epibenthic organisms becoming important during the winter months. Feeding occurs mainly at night in surface waters. Age-0 pollock are most frequently associated with gelatinous zooplankton (medusae) and older pollock. Many predators on age-0 pollock have been identified; the most important are arrowtooth flounder ( Atheresthes stomias ), adult pollock, puffins ( Fratercula spp.), murres ( Una spp.), harbor seals ( Phoca vitulina richardsi ) and Steller sea lions ( Eumetopiasjubatus ). Modelling provides some insight into the population dynamics of these juveniles and environmental conditions which interannually affect their survival. These results are discussed relative to the importance of age-0 pollock in the recruitment of this species and to their role in the pelagic ecosystem.     

鱼类在内分泌干扰研究中的应用

鱼类在毒理学研究和生态风险评价中有重要的试验价值,是研究内分泌干扰作用的理想试验动物。本文主要综述了利用鱼类进行内分泌干扰研究的主要测试终点和敏感效应指标;重点介绍了稀有鮈鲫、斑马鱼、日本青鳉、孔雀鱼、剑尾鱼、黑头软口鲦等鱼类的主要生物学特性,以及利用它们进行内分泌干扰物的筛选与测试方面的研究成果。     

Evaluation of a Biofloc System for Intensive Culture of Fathead Minnows,Pimephales promelas

This study was carried out to test the suitability of biofloc technology to improve the productivity of the fathead minnow, Pimephales promelas, a commercially important baitfish in North America. Biofloc growth was induced in treatment tanks by periodic additions of a carbon source (glucose) to maintain a C : N ratio of 12:1. Control tanks (no aeration and no carbon addition) accommodated densities equivalent to 1 million fish/ha, while treatment tanks (biofloc) had densities of 1, 2, 4, and 8 million fish/ha. Fish were fed 4% body weight using a 32% protein commercial diet. There were no significant differences in condition of fish harvested from control and treatment densities (P < 0.05). However, fish growth indicators such as final individual weight, feed conversion efficiency, and specific growth rate were significantly impaired at higher stocking densities. Survival rate was significantly lower in the 8 million/ha treatment (P < 0.05). Results were indicative of possible production efficiencies of twofold higher in biofloc systems stocked at or below 4 million/ha compared with traditional ponds. Although biofloc systems maintained the desired water‐quality parameters, biofloc microbial biomass did not seem to significantly enhance feed conversion and specific growth rates of fathead minnows.     

Potential population and assemblage influences of non‐native trout on native nongame fish in Nebraska headwater streams

Non‐native trout are currently stocked to support recreational fisheries in headwater streams throughout Nebraska. The influence of non‐native trout introductions on native fish populations and their role in structuring fish assemblages in these systems is unknown. The objectives of this study were to determine (i) if the size structure or relative abundance of native fish differs in the presence and absence of non‐native trout, (ii) if native fish‐assemblage structure differs in the presence and absence of non‐native trout and (iii) if native fish‐assemblage structure differs across a gradient in abundances of non‐native trout. Longnose dace Rhinichthys cataractae were larger in the presence of brown trout Salmo trutta and smaller in the presence of rainbow trout Oncorhynchus mykiss compared to sites without trout. There was also a greater proportion of larger white suckers Catostomus commersonii in the presence of brown trout. Creek chub Semotilus atromaculatus and fathead minnow Pimephales promelas size structures were similar in the presence and absence of trout. Relative abundances of longnose dace, white sucker, creek chub and fathead minnow were similar in the presence and absence of trout, but there was greater distinction in native fish‐assemblage structure between sites with trout compared to sites without trout as trout abundances increased. These results suggest increased risk to native fish assemblages in sites with high abundances of trout. However, more research is needed to determine the role of non‐native trout in structuring native fish assemblages in streams, and the mechanisms through which introduced trout may influence native fish populations.     

Behavioural determinants of distribution and survival in early stages of walleye pollock, Theragra chalcogrammai a synthesis of experimental studies

This review summarizes results of an extensive series of laboratory studies on the behavioural responses of early life stages of walleye pollock, Theragra chakogramma to key environmental factors including light, temperature, gravity, turbulence, food availability and predator presence. Experiments focused on vertical distribution of egg through 0-age stages, and social interactions of age-0 juveniles. Key factors were modified either singly or in concert to determine their direct and indirect influence on fish behaviour. The observed results suggest that the behaviour of individual fish depends on the integration of a continually changing hierarchy of both intrinsic and extrinsic factors, with the relative importance of a specific factor varying with ontogeny and over time and space. The broad range of responses displayed by early life stages suggests that behaviour plays an important role in determining the consequences of environmental variability on walleye pollock populations. In general, results from our laboratory experiments are consistent with patterns observed in field studies, supporting the efficacy of using experimental behavioural research to define some of the underlying mechanisms controlling distribution and survival in the field, and eventual recruitment to adult populations.