Nutritional Ecology of Pinfish (Lagodon rhomboides)

Figure 1. Lagodon rhomboides - the pinfish

Why study pinfish?

Pinfish are the numerical dominant species in seagrass meadows in the Southeastern USA
Pinfish comprise a major trophic link between seagrasses and piscivores (including various fishes such as flounders, seatrouts, and drums and the mammal bottlenose dolphin)
Pinfish are commercially important in the live-fish-for-consumption, baitfish, aquarium fish trades
They are true omnivores, undergoing an ontogenetic change in diet as they grow.
They steal your bait!

Pinfish get nutrition from plants and animals (omnivory)

Figure 2: A portion of the food web in a seagrass meadow. Seagrass, detritus, and algae forms the base of the web, various invertebrates consume seagrass or detritus, and pinfish (on right) and spot (Leiostomus xanthurus on left) compete for foods as they grow. Pinfish eat the seagrass directly when they grow larger than 100 mm SL. Pinfish and spot are eventually eaten by piscivores, represented here by gulf flounder (Paralichthys albigutta).

When they first arrive in seagrass meadows as post-larvae, pinfish feed on harpacticoid copepods, amphipods, and polychaetes (Figure 2). They are < 40 mm SL at this stage, which occurs from December through June each year.
At sizes larger than 40 mm SL, they start to consume producers like diatoms and algae, thus shifting towards lower trophic levels as they grow.
Pinfish > 100 mm SL consume large amounts of seagrass such as shoal grass, Halodule wrightii, eelgrass, Zostera marina, manatee grass, Syringodium filiforme, and turtle grass, Thalassia testudinum.

Can seagrass be a source of energy for pinfish?

Figure 3. A Thalassia testudinum seagrass meadow where pinfish lurk. Photograph from St. Joe Bay, Florida (photo by Ron Phillips from the Univ. of Hawaii's Seagrass Home Page)

Figure 4. Seagrass (Zostera marina) inside a 120 mm SL pinfish stomach collecetd in Core Sound, NC. Some pinfish have > 90 % of their gut contents composed of seagrasses. Note the bite-sized pieces of the leaves. (photo by Joe Luczkovich)

Figure 5. A scanning electron micrograph of rod-shaped cellulolytic symbiotic bacteria from pinfish intestines. (Photo by Tim Charles, ECU SEM laboratory)

Seagrasses (Figure 3) have lots of cellulose that must be broken down before the pinfish can obtain any energy from the seagrass.
Pinfish can bite through the seagrass blades and begin the process of digestion by biting through the blades (Figure 4).
The enzyme needed to break down the blades further is cellulase, but it is not normally made by fishes.
Our research demonstrates that pinfish are able to obtain energy from cellulose in their diet with the assistance of symbiotic cellulolytic bacteria (Figure 5).
Radiolabeled cellulose injected into pinfish intestines was assimilated by pinfish in significant amounts.
The cellulose can be broken down by the cellulase produced by the symbiotic bacteria.
The cellulolytic bacteria are obligate anaerobes that dwell in the intestine of the pinfish and ferment the seagrass.
The anaerobic bacteria use the glucose released during cellulose fermentation.
The metabolic by-products of bacteria fermentation are various volatile fatty acids (VFAs) such as acetic acid, butyric acid, and proprionic acid.
Pinfish assimilate the volatile fatty acids and may gain an energtic benefit from this symbiotic association.
Click here to see the VFA profiles for pinfish intestinal bacteria collected over a range of fish sizes. The shift in diet from carnivory at small sizes to herbivory at large sizes appears to influence the type of VFA detected in the intestinal tract.
Small fish have the greatest diversity of VFA types, and large fish have less VFA diversity.

Who studies pinfish?

Joseph J. Luczkovich, Associate Scientist, Institute for Coastal and Marine Resources and Visiting Associate Professor Department of Biology, East Carolina University, Greenville, NC 27858 luczkovichj@mail.ecu.edu
Edmund Stellwag, Associate Professor, Department of Biology, East Carolina University, Greenville, NC 27858 stellwage@mail.ecu.edu
Gary Burr, MS Biology candidate Department of Biology, ECU (present address at University of Maryland, Department of Biochemistry) burr0522@earthlink.net

Publications on pinfish:

Luczkovich, J. J., B. Rizzo, H. Neckles, G. P. Ward, and R. R. Christian. Modeling trophic impacts of fishes on taxa ranging from bacteria to birds in a seagrass food web. Submitted to Ecological Monographs.
Luczkovich, Joseph J., Stephen F. Norton, and R. Grant Gilmore, Jr. 1995. The influence of oral anatomy on prey selection during ontogeny of two percoid fishes, Lagodon rhomboides and Centropomus undecimalis. Environmental Biology of Fishes, Vol. 44: 79-95.
Luczkovich, Joseph J. and E. J. Stellwag. 1993. Isolation of cellulolytic microbes from the intestinal tract of the pinfish, Lagodon rhomboides: size-related changes in diet and microbial abundance. Marine Biology 116: 389-379.
Stellwag, E.J. T. D. Smith, and J. J. Luczkovich. 1995. Characterization and ecology of carboxymethycellulase-producing anaerobic bacterial communities associated with the intestinal tract of the pinfish, Lagodon rhomboides. Applied and Environmental Microbiology, February 1995, 813-816.
Luczkovich, J. 1988. The role of prey detection in the selection of prey by the pinfish, Lagodon rhomboides (Linnaeus). Journal of Experimental Marine Biology and Ecology. 123: 15-30.