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Abstract The axial musculature of fishes has historically been characterized as the powerhouse for explosive swimming behaviors. However, recent studies show that some fish also use their ‘swimming’ muscles to generate over 90% of the power for suction feeding. Can the axial musculature achieve high power output for these two mechanically distinct behaviors? Muscle power output is enhanced when all of the fibers within a muscle shorten at optimal velocity. Yet, axial locomotion produces a mediolateral gradient of muscle strain that should force some fibers to shorten too slowly and others too fast. This mechanical problem prompted research into the gearing of fish axial muscle and led to the discovery of helical fiber orientations that homogenize fiber velocities during swimming, but does such a strain gradient also exist and pose a problem for suction feeding? We measured muscle strain in bluegill sunfish,Lepomis macrochirus,and found that suction feeding produces a gradient of longitudinal strain that, unlike the mediolateral gradient for locomotion, occurs along the dorsoventral axis. A dorsoventral strain gradient within a muscle with fiber architecture shown to counteract a mediolateral gradient suggests that bluegill sunfish should not be able to generate high power outputs from the axial muscle during suction feeding—yet prior work shows that they do, up to 438 W kg−1. Solving this biomechanical paradox may be critical to understanding how many fishes have co-opted ‘swimming’ muscles into a suction feeding powerhouse.
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Habitat-Specific Foraging Strategies and Polymorphic Variation of Bluegill Sunfish, Lepomis macrochirus
As generalists, Bluegill Sunfish (Lepomis macrochirus) feed in densely vegetated littoral and pelagic zones. Paradoxically, being a generalist requires that Bluegill adopt habitat-specific foraging strategies in order to successfully exploit local environments. To better understand their foraging behaviors, underwater cameras were deployed in different locations of Lake Waban, MA to reflect the diversity of local habitats within the lake. We identified three foraging strategies: hunting, grazing, and pelagic feeding. Each strategy is categorized as opportunistic or intentional and some are further subdivided into several modalities. Hunting occurs in shallow littoral zones, is intentional, often performed in groups, and is characterized by repeating cycles of burst-coast-stop-search until prey is visually detected. Grazing also occurs in shallow littoral zones, but is either intentional or opportunistic, and is characterized by three modalities depending on vegetation type. Active grazing involves biting and pulling on pondweed, whereas passive grazing involves hovering near milfoil and delicate suction feeding, and surface grazing involves searching beneath lily pads and explosive bouts of suction feeding. Pelagic feeding occurs in deep open water, is often opportunistic, may occur in groups, and is characterized by intermittent swimming from one morsel to the next. Some correlation exists between phenotype, age, and foraging strategy. For example, darker and deeper bodied adults engage in hunting, whereas lighter and fusiform Bluegill of all ages engage in pelagic feeding. These observations demonstrate the complex behaviors that characterize a paradigmatic generalist and illustrate the multitude of variables that impact their specific feeding strategies.
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- PAR ID:
- 10276557
- Date Published:
- Journal Name:
- Integrative and comparative biology
- Volume:
- 61
- Issue:
- Supplement_1
- ISSN:
- 1557-7023
- Page Range / eLocation ID:
- E1227-E1228
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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