The diet of largemouth bass, Micropterus salmoides, in Lake Naivasha, Kenya

Lake Naivasha is a freshwater lake situated in the eastern rift valley of Kenya. Only five species of fish are present, all of which have been introduced. Of these, Oreochromis leucostictus, Tilapia zillii and Micropterus salmoides (largemouth black bass) support an important gillnet fishery with bass also being taken for sport. Until bass reached 260 mm f.l. they depended upon invertebrate food organisms. Thereafter crayfish, fish and frogs became increasingly important the larger the size of the bass. The most important invertebrate prey species was the water boatman, Micronecta scutellaris , followed by chironomid and culicid pupae. Zooplank-ton was consumed but only in large quantity by fish smaller than 80 mm. For bass over 260 mm the crayfish, Procambarus darkii , was the principal food. The largemouth bass in Lake Naivasha are generalized macro-predators, feeding principally on free-living animals of a kind most likely to be found in the littoral zones.     

Muscle function and power output during suction feeding in largemouth bass, Micropterus salmoides

Muscle power output is thought to limit suction feeding performance, yet muscle power output during suction feeding has never been directly measured. In this study, epaxial activation and strain, hyoid depression, and intra-oral pressure were simultaneously measured during suction feeding in the largemouth bass (Micropterus salmoides). A mechanical model of muscle force transmission between the neurocranium and oral cavity was used to estimate muscle stress, work, and power. The epaxials shortened from rest an average of 9% of their length, with the highest efforts producing greater than 20% strain. Onset of shortening was simultaneous with or shortly after (< 10 ms) onset of activation. Maximal net power for individual fish ranged from 17 to 137 W kg(-1). Muscle power was significantly correlated with rectified EMG area (r = 0.80; p < 0.0001). The power required for cranial expansion was significantly correlated with epaxial power (r = 0.81; p < 0.0001), and the power exponent of this relationship ( approximately 1 for 3 of the 4 fish) implies that epaxial power accounts for most of the power of cranial expansion. The limitations imposed by the kinematic requirements and loading environment of suction feeding (short delay between activation and strain, maximal stress occurring after shortening, operation at lengths shorter than resting length) may prevent maximal muscular power production.     

Effects of sulphuric acid exposure on the behaviour of largemouth bass,Micropterus salmoides

Synopsis Young-of-the-year largemouth bass,Micropterus salmoides, were exposed to four concentrations of sulphuric acid (pH levels 7.2, 6.1, 4.8, and 3.7) for 30 days, and the frequencies of feeding acts and activity bouts, and time budgets were recorded. Juveniles at pH 6.1 and at pH 4.8 performed the two feeding acts, bites and orientations, more often, and spent more time feeding than bass at pH 7.2. Bass at pH 3.7, however, reduced feeding, and spent a significantly larger portion of their time hovering in the water column. Frequencies of comfort and agonistic acts increased with a decline in pH. Alterations of behavioural repertoires of young-of-the-year largemouth bass were useful indicators of sulphuric acid exposure.     

Ontogenetic diet shifts and interrupted piscivoryin introduced largemouth bass (Micropterus salmoides)

The ecology of largemouth bass (Micropterus salmoides) is one of the best known for freshwater fish, though largely through studies within its native range (North America). I studied the habitat and diet of a bass population introduced into a Mediterranean lake. The bass displayed strong ontogenetic diet shifts as follows: young‐of‐the‐year <25 mm fed on microcrustaceans; fish 25–75 mm, on amphipods and insects; fish 100–225 mm, on a freshwater shrimp, small fish and insects; fish 250–300 mm, on shrimp or crayfish; and fish >300 mm, on crayfish and large fish. The diet showed several differences from most previous studies: importance of freshwater shrimp instead of insects, low piscivory, and a delay in the ontogenetic shift to piscivory. Moreover, the ontogenetic shift to piscivory was interrupted at 250–300 mm, with consumption of shrimp and crayfish. This interruption of piscivory has been largely unreported and seems a consequence of the size‐structure and species composition of the fish assemblage. A review of the literature suggests that piscivory by largemouth bass might be generally lower in populations introduced outside North America.     

Considerations of blood parameters of largemouth bass, Micropterus salmoides

To evaluate physiological stress resulting from environmental influences, a haematological study of a natural population of largemouth bass, Micropterus salmoides , was undertaken to establish a 'normal' blood profile. Several parameters including haemoglobin concentration, haematocrit, erythrocyte count, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, plasma protein concentration and glucose levels were investigated. Haematocrit, haemoglobin, and total plasma protein were positively correlated with fish length. Haemoglobin and haematocrit were positively correlated with fish age while mean corpuscular haemoglobin, concentration was negatively correlated with fish age. Both haemoglobin and haematocrit values were related to erythrocyte counts.     

Scaling of in vivo muscle velocity during feeding in the largemouth bass, Micropterus salmoides (Centrarchidae)

Many vertebrates undergo large increases in body size over the course of a lifetime, and these increases are often accompanied by changes in morphological and physiological parameters. For instance, in most animals, increases in size with growth are accompanied by decreases in the maximum speed of shortening (V(max)) in locomotor muscles. Curiously, in muscles involved in suction feeding, V(max) shows no decreases with size in vitro, despite the fact that timing of kinematic events involved in suction feeding (e.g., time to peak gape) slow with increased size. The goal of this study was to examine whether muscular speed in vivo varies with size during suction feeding in the largemouth bass (Micropterus salmoides). The dorsal epaxial musculature of 10 individual bass (varying from 123 to 685 g and from 18.1 to 32.0 cm standard length [SL]) was implanted with sonometric crystals to measure muscle length during feeding on elusive prey (large goldfish). No relationship was found between the mean individual or maximum speed of shortening with mean individual log-transformed SL. However, mean magnitude of shortening and maximum shortening magnitude showed nonsignificant increases with SL ([Formula: see text] and 0.06, respectively). Average duration of shortening was found to increase with log-transformed SL. The size invariance of observed shortening velocity in the epaxial muscles during feeding may stem from size invariance of imposed loads during suction feeding. This is in contrast to what is normally seen in locomotor systems where loads on muscles often increase with body size.     

Predator-prey behaviour of fathead minnows, Pimephales promelas and largemouth bass, Micropterus salmoides in a model ecosystem

The predator-prey behaviours displayed by largemouth bass, Micropterus salmoides and fathead minnows, Pimephales promelas , were investigated. Fathead PRMOWS were subjected to predation by largemouth bass and observed in a model system that was designed to mimic a natural ecosystem. Anti-predator devices utilized by fathead minnows include schooling, surface swimming, formation of a circular aggregation, and seeking refuge under vegetation.     

The complete mitochondrial genomes of largemouth bass of the northern subspecies (Micropterus salmoides salmoides) and Florida subspecies (Micropterus salmoides floridanus) and their applications in the identification of largemouth bass species

The largemouth bass belongs to the family Centrarchidae, which includes two subspecies: the northern subspecies, Micropterus salmoides salmoides, and the Florida subspecies, Micropterus salmoides floridanus. In this study, the complete mitochondrial genomes of the two subspecies were sequenced, and their genetic differences were identified. The mitogenomes of M. s. salmoides and M. s. floridanus are 16,486 and 16,479?bp in length, respectively. The two subspecies consisted of 37 genes (13 protein-coding genes, 2 ribosomal RNA, and 22 transfer RNA), which are typical for vertebrate mtDNA. Phylogenetic analysis provided statistical support for the monophyly of the family Centrarchidae. Comparison of the two subspecies' mitogenomes revealed a relatively high number (450) of single nucleotide polymorphisms (SNPs) in protein-coding genes. We characterized SNPs in the partial cytochrome c oxidase subunit 1 gene of different individuals from three cultured populations, one wild northern subspecies population, and one wild Florida subspecies population. Twenty-eight SNPs were fixed with alternative nucleotides in the two subspecies, which could be used for differentiating them. Based on this gene, phylogenetic tree and genetic distance analyses supported that cultured largemouth bass in China belongs to the northern subspecies.     

Utilizing stomach content and faecal DNA analysis techniques to assess the feeding behaviour of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus

In this study, the feeding behaviour of the non‐native invasive predatory fishes largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus was studied in the Ezura River, a northern tributary of Lake Biwa, Japan. Prey composition was estimated based on visual examination of stomach contents and faecal DNA analysis to determine feeding habits of these predatory fishes. Stomach content analysis showed that native fishes (e.g. ayu Plecoglossus altivelis and gobies Rhinogobius spp.) and shrimps (e.g. Palaemon paucidens) were the major prey items for M. salmoides, while snails, larval Chironomidae and submerged macrophytes were the dominant prey items of L. macrochirus. Micropterus salmoides tended to select larger fish in the case of crucian carp Carassius spp., but smaller fishes in the case of P. altivelis and Rhinogobius spp. Faecal DNA analyses revealed prey compositions similar to those identified in predator stomach contents, and identified additional prey species not detected in stomach content inspection. This study demonstrated that both stomach content inspection and DNA‐based analysis bear several inherent shortcomings and advantages. The former method is straightforward, although identification of species can be inaccurate or impossible, whereas the latter method allows for accurate species identification, but cannot distinguish prey size or stage. Hence, integration of morphology‐based and DNA‐based methods can provide more reliable estimates of foraging habits of predatory fishes.     

Hunting behavior of Florida largemouth bass, Micropterus salmoides floridanus, in a channelized river

The distribution and behavior of Florida largemouth bass, Micropterus salmoides floridanus, and their main prey (sunfish, genus Lepomis, and the cichlid Tilapia mariae) were studied in southern Florida to determine how fish behave in the simplified habitats found in channelized rivers. Time budgets were constructed from focal animal observations on 69 bass. Patterns of behavior associated with hunting were performed during a significantly higher proportion of the time when bass were in vegetated habitats. Scan samples of the behavior of 236 observed bass revealed that hunting was more common in areas of high structural complexity. Only 38% of observed bass were solitary, with the majority occurring in groups with either conspecifics or in mixed-species groups with similar sized bluegill sunfish, Lepomis macrochirus. Largemouth bass (n=1014) and sunfish (n=1372) were significantly more abundant in areas with vegetation and were almost entirely absent from the water column in the center of the canal. All species of fish avoided the water column, where currents were swift and no cover was available. The structure of the habitat appears to be important in the way largemouth bass organize their activity patterns. This suggests that habitat availability in channelized rivers significantly influences important behaviors such as hunting, thus potentially altering energy budgets and population dynamics of both predator and prey.     

Molecular characterization of a ranavirus isolated from largemouth bass Micropterus salmoides.

An iridovirus, isolated from largemouth bass Micropterus salmoides following a die-off among adult fish and provisionally designated largemouth bass virus (LMBV), was characterized by analysis of viral protein synthesis in infected cells, viral DNA restriction fragment length polymorphisms (RFLP), and sequence determination of the major capsid protein and viral DNA methyltransferase genes. All 3 approaches yielded results consistent with the suggestion that LMBV was a member of the genus Ranavirus. Moreover, LMBV was nearly identical to 2 isolates from Southeast Asia which had been previously detected in imported ornamental fish. It remains to be determined whether infection of largemouth bass resulted from exposure to an imported virus, or whether the presence of similar viruses in southeast Asia and the southeastern United States indicates that iridovirus species are not geographically limited as suggested earlier, but rather globally distributed.     

A successful population of largemouth bass, Micropterus salmoides, in a subtropical lake in Mozambique

Sectioned otoliths were used for age and growth determination of the alien Micropterus salmoides from Lake Chicamba, a hydroelectric dam in central Mozambique. Marginal zone analysis showed that annulus formation occurred during winter in August and September. The maximum estimated age was 5 years. Growth was described by the 3 parameter von Bertalanffy model as L_t=465.51 (1 – e^{-1.175(t+0.009)}) mm FL. Juvenile growth rate was 23.1 mm per month during their first 7 months of life. The age at 100% maturity was 0.9 years, and spawning occurred during August and September. The juvenile fish fed sequentially on the most abundant prey items. Spawning occured before any of the indigenous fish species and so, there is little inter-specific competition. Conspecific juveniles formed the most important constituent in the adult M. salmoides diet from October to December when alternative prey was limited. The total annual mortality rate (Z) for the species in Lake Chicamba was 1.27 yr^-1, the mean empirical estimate of natural mortality (M) was 0.73 yr^-1, and fishing mortality (F) was calculated at 0.54 yr^-1. The success of M. salmoides in Lake Chicamba was attributed to limited inter-specific and intra-specific competition for prey as a consequence of the timing of the spawning, cannibalism and high mortality rates.     

Seasonal aspects of daily ration and diet of largemouth bass,Micropterus salmoides,with an evaluation of gastric evacuation rates

Synopsis Sample of stomach contents collected on 10 dates from May to October, 1978, were used to describe the diet and estimate the daily ration of subadult largemouth bass (primarily age-III fish) in Lake Rebecca, Minnesota. The method of Elliott & Persson (1978) was used to estimate daily ration. Data from sources in the literature were used to quantify gastric evacuation, which was found to be adequately described by an exponential decay model. The exponent of gastric evacuation increased exponentially with temperature. Seasonal changes in the diet with respect to composition, distribution of food among stomachs, and food particle size were reflected in the seasonal pattern of growth. Weight gain and the formation of scale annuli did not occur until the diet shifted from large bluegills and insects to age-0 largemouth bass and bluegills. Estimates of daily ration ranged from almost zero in mid-May and early June to over 5% in late August. The use of median weights of stomach contents was found to yield more meaningful estimates of the daily ration of individual bass than those based on means. Estimates based on medians were consistent with the observed pattern of growth and with information on maintenance rations and satiation levels. A growth-limiting lack of suitably-sized forage fish apparently occurred in the early part of the growing season.Paper Number 11,657, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul, MN. 55108.     

Observations on the ecology of Clinostomum marginatum in largemouth bass (Micropterus salmoides)

Over a fifteen month period, beginning October, 1974, approximately 13 500 centrarchids were examined for evidence of infection with metacercaria of Clinostomum marginatum. Species checked included Lepomis macrochirus, L. gulosus, L. auritus, Pomoxis nigromaculatus and Micropterus salmoides. The study site was Par Pond (South Carolina, U.S.A.), an 1120 ha reservoir receiving thermal effluent from a nuclear production reactor. Except for the largemouth bass, M. salmoides , infection percentages among the five species were less than 1%. Among bass, infection varied seasonally, being highest from January to June. From the spring highs of approximately 25 %, the percentages dropped to lows of < 10% in July and August; there was a jump in September-October to another peak of 30% and then a steady decline through December when infection percentages were again less than 10%. Neither body condition nor length of the bass were related to infection percentage or metacercaria density. Infection percentage could not be related to the influence of thermal effluent. Infection percentages did vary from location to location within the Par Pond system. A significant rank correlation could be established between infection percentage and the amount of littoral zone present in the locality from which the bass were taken. It is suggested that the local 'bay effects' are the result of limited home and foraging ranges of the bass in relation to the amounts of littoral zone present in various locations of the reservoir.     

The effects of temperature change on the hatching success and larval survival of largemouth bass Micropterus salmoides and smallmouth bass Micropterus dolomieu

In this study, the effects of abrupt temperature change on the hatching success and larval survival of eggs, yolk-sac larvae (YSL) and larvae above nest (LAN), for both largemouth bass Micropterus salmoides and smallmouth bass Micropterus dolomieu were quantified. Temperature had a significant effect on hatching success and time to 50% mortality, with large heat shocks causing accelerated mortality. The temperature changes shown to influence survival of all life stages, however, were beyond what is typically experienced in the wild. Micropterus salmoides had greater egg hatching success rates and increased survival rates at YSL and LAN stages, relative to M. dolomieu. Additionally, egg hatching success and survival of LAN varied across nests within the study. These findings suggest that temperature alone may not account for variations in year-class strength and may emphasize the need for protection of the nest-guarding male Micropterus spp. to ensure recruitment.     

Interaction of bass tapeworm, Proteocephalus ambloplitis, and Neoechinorhynchus sp. (Acanthocephala) in largemouth bass, Micropterus salmoides

The number of plerocercoids of the bass tapeworm, Proteocephalus ambloplitis, in wild largemouth bass was negatively correlated (r = -0.94) with the number of Neoechinorhynchus sp. Competitive inhibition between the 2 parasites appeared to exist. Similarly, the numbers of Neoechinorhynchus sp. in wild bass decreased when adult bass tapeworms were present in the intestine. Proteocephalus ambloplitis plerocercoids used to challenge bass vaccinated with either P. ambloplitis adult or Neoechinorhynchus sp. antigens were smaller (P less than 0.05) when recovered than those used to challenge control bass. Based on preliminary results, both antigens might have enabled the bass to limit growth and/or development of the invading bass tapeworm, plerocercoids. Cross-protective immunity may be the reason for this occurrence, in which case, it could offer an explanation for competitive inhibition existing between P. ambloplitis and Neoechinorhynchus sp.     

The influence of brood loss on nest abandonment decisions in largemouth bass Micropterus salmoides

Largemouth bass Micropterus salmoides broods were experimentally reduced in size to test whether brood size (BS) and simulated brood depredation affect the decision by a male to continue providing care for its brood or to abandon that brood prematurely before its offspring reach independence. The highest ranked of the generalized linear models predicting brood abandonment was based on the number of offspring remaining in a nest following brood devaluation, indicating that parental male fish reassess the value of a brood following perturbation. Paternal M. salmoides were more likely to abandon their broods if initial BS was small before devaluation, and if there was a greater decrease in BS, indicating a threshold for both the amount of brood loss and remaining BS. Larger, older males were also less likely to abandon their brood than smaller, younger conspecifics. These results have broad implications for determining drivers of parental care trade‐offs and how individuals assess the value of a brood.     

Experimental trophic ecology of juvenile largemouth bass,Micropterus salmoides,and blue tilapia,Oreochromis aureus

Synopsis The potential for feeding competition between largemouth bass, Micropterus salmoides, and blue tilapia, Oreochromis areus, in Lake Fairfield, Texas was evaluated experimentally. Largemouth bass and blue tilapia were grown in cages alone and in combination with each other. The fish were allowed to feed on the natural food within the lake. Largemouth bass grown in combination with blue tilapia were significantly shorter and weighed less than largemouth bass grown alone. Blue tilapia grown in combination with largemouth bass were statistically significantly longer and heavier than blue tilapia grown alone. Largemouth bass grown alone had diets (volume and number of food items) significantly different than the largemouth bass grown with the blue tilapia. Largemouth bass fed primarily on chironomid larvae and pupae, and odonates, whereas blue tilapia consumed vegetable matter, detritus, and chironomid larvae. Length and weight differences between large-mouth bass grown alone and in combination with blue tilapia, in conjunction with the largemouth bass diet shift, support the theory that these two species compete for food resources.     

Examining the effects of chronic,lake-wide elevated temperatures on behavioural expression in largemouth bass,Micropterus salmoides

Many behaviours have differential fitness consequences across thermal and ecological contexts, indicating that both ecological shifts and warming temperatures induced by climatic change may alter how organisms behave. However, empirical evidence of temperature-driven behavioural selection in natural systems is lacking. We compared behaviours and behavioural syndromes related to activity, exploration, boldness and aggression in populations of largemouth bass (Micropterus salmoides) from ambient lakes to the those from artificially warmed, power plant cooling lakes to investigate changes in behaviours associated with warmer environments. Activity, exploration, boldness and aggression of juvenile largemouth bass were assessed in laboratory conditions using a novel environment assay and a risky situation assay. We found that activity and exploratory behaviours were higher and decreased through first year ontogeny in populations from heated lakes, whereas these behaviours were lower and showed no relationship through ontogeny in populations from ambient lakes. We attribute these differences to the changes in food source availability in heated lakes associated with temperature-driven ecological effects. Bold and aggressive behaviours tended to differ between populations, as did correlations between behaviours, but did not differ between ambient and heated lakes. The findings of this work identify that large ecological changes associated with warming environments, such as food availability, may drive changes in some aspects of behavioural expression in largemouth bass but that other aspects of behavioural expression may be driven by lake-specific factors not related to warming.