The Progressive Fish- Culturist 51 :101-104 1989
Predation by Striped Bass and Striped Bass X White Bass
HYBRIDS ON REDBELLY TILAPIA AND COMMON CARP
Fish and Aquaculture Research Station
GERALD T. KLAR1 AND NICK C. PARKER2
U.S. Fish and Wildlife Service
Route 3, Box 86
Marion, Alabama 36756, USA
Abstract.—In laboratory experiments conducted to evaluate the suitability of redbelly tilapia (Tilapia zilli) and common carp (Cyprinus carpio) as forage for striped bass (Morone saxatilis) and hybrids of striped bass ´ white bass (M. chrysops), the hybrids ate larger redbelly tilapias than did striped bass, but striped bass ate the larger common carp. The mean vertical buccal gape of striped bass and hybrids did not differ significantly over the length range of predators tested. The maximum body depths of the prey consumed were about 30% smaller than the vertical gapes of the predators. Although girth of common carp was larger than girth of redbelly tilapias of the same length, striped bass ate larger common carp than redbelly tilapias. The selection of larger redbelly tilapias by hybrids than by striped bass suggested that hybrids were the more aggressive.
Striped bass (Morone saxatilis) and hybrids of striped bass ´ white bass (M. chrysops) have been stocked in more than 450 freshwater reservoirs in the USA to help control clupeid populations and to support sport fisheries without adversely affecting native fish populations (Stevens 1984). Food of young-of-the-year striped bass differs with age, size, and habitat. Young striped bass (10-30 mm total length, TL) feed first on adult copepods and cladocerans and then on insect larvae as the fish increase in size (Harper et al. 1969). Fish and insect larvae are the most important foods of striped bass longer than 100 mm TL (Humphries and Cumming 1973). Curry (1981) found that striped bass introduced into small impoundments fed more frequently on small largemouth bass (Micropterus salmoides) than on sunfishes (Lepomis spp.); after largemouth bass became too large to be preyed upon, however, the striped bass ate sunfishes. Hybrids of striped bass and white bass in an Oklahoma reservoir selected gizzard shad (Dorosoma cepedianum) and underutilized inland silversides (Menidia beryllina), sunfishes (Lepomis spp.), and crappies (Pomoxis spp.), whereas largemouth bass selected gizzard shad, sunfishes, and crappies (Gilliland and Clady 1984). Clark and Pearson (1979) reported that postlarval white bass 7-12 mm standard length fed on postlarvae of common carp (Cyprinus carpio).
1 Present address: U.S. Fish and Wildlife Service, Marquette, Michigan 49855, USA.
2 Present address: Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, Texas 79409-2125, USA.
Common carp and tilapia (Tilapia spp.) are reared in polyculture for commercial purposes, as well as to control vegetation in fish culture ponds (Hepher and Pruginin 1981). In the polyculture or monoculture of yearling common carp and tilapias, both species produce numerous young that remain small owing to overcrowding and resultant stunting. The small fingerlings compete with larger fish for both natural food and pelletized rations. The excess fingerlings in these culture situations may serve as forage for predators such as striped bass or striped bass hybrids.
To evaluate the relative suitability of redbelly tilapia (Tilapia zilli) and common carp as forage for striped bass and hybrids, we offered fingerlings of both prey species to these predators to determine the relationship between predator and prey size.
Redbelly tilapia, striped bass, and hybrid striped bass were obtained from laboratory stocks at the Southeastern Fish Cultural Laboratory, Marion, Alabama; common carp came from Auburn University, Auburn, Alabama. All fish were acclimated to laboratory conditions and reared in 1.5m3 fiberglass tanks in aerated well water (22°C) for at least 2 weeks before the predation experiments were begun. All fish were fed trout pellets (40% protein) ad libitum daily during the acclimation period.
Three experiments were conducted to determine the maximum consumable size of redbelly tilapia and common carp by striped bass and of redbelly tilapia by hybrids (Table 1). Three striped bass or hybrids were used as predators in each trial. The predators were taken off feed for 24 h, anesthetized with 0.02% tricaine (MS-222) in a 1 % salt solution, weighed, measured for total length, and stocked into experimental tanks. The size difference between the three predators did not exceed 0.5 cm. Striped bass or hybrids 100 mm long or less were stocked into 0.7-m3 polyethylene tanks; longer fish were stocked into 1.5-m3 fiberglass tanks. The tanks were fitted with a center standpipe and drain; each tank received 22°C aerated well water. To begin a trial, we measured and weighed six redbelly tilapias or six common carp and stocked them into the tank with three predators. After 24 h, we removed and measured the prey that remained and measured a new group of prey and put them in the tank. The maximum length difference within each group of six prey fish was 0.5 cm; successively larger prey were presented in groups of six to the predators in the series of tests. We established the maximum size of prey acceptable to the predators as being just below the size of fish that were not consumed for three consecutive days. Linear, log, and quadratic regression curves were fitted to the data; the best fits were provided by the quadratic model Y= a + bX + cX2; Y= predator total length (mm), X = prey total length (mm), and a, b, and c were empirically determined constants.
Vertical buccal gape of striped bass and hybrids was measured with a caliper as the maximum vertical opening between the anterior ends of the upper and lower jaws. The relation between buccal gape-and total length of 76 striped bass and 97 hybrids was evaluated by regression analysis. Linear regressions of body depth on total length were developed for 93 redbelly tilapias (28-143 mm TL) and 85 common carp (47-135 mm TL).
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TABLE 1.—Total lengths of predators and prey in three experiments to evaluate the size of redbelly tilapia and common carp selected by striped bass and striped bass hybrids.
Analysis of covariance was used to detect significant differences (P £ 0.05) in regression coefficients and adjusted means between body depth of redbelly tilapia and common carp, between mouth size of striped bass and hybrids, and among predator-prey relations.
Results and Discussion
Neither striped bass nor hybrids ate prey as large as their gapes would allow. They fed in a manner similar to that reported for largemouth bass (Lawrence 1958); striped bass and hybrids usually took the prey into their mouth head first and turned the prey on its side before swallowing it. Hybrids ate significantly longer redbelly tilapias (adjusted mean ± SD, 69.7 ± 1.0 mm TL) than did striped bass (59.4 ± 0.8 mm TL) of equal length. Striped bass ate significantly longer common carp (82.1 ± 1.1 mm TL) than they did redbelly tilapias (65.9 ± 0.9 mm TL; Figure 1). Relations between total length and body depth indicated that common carp longer than 67 mm TL were deeper bodied than redbelly tilapias of similar length; at shorter lengths, however, redbelly tilapias were the deeper bodied (Figure 2). Slopes of the regression lines of body depth on total length differed significantly (P £ 0.05) between the prey species.
There was no significant difference between the average gapes of striped bass (mean adjusted for length ± SD, 25.6 ± 0.3 mm) and hybrids (26.2 ± 0.3 mm) over the range of body lengths tested; however, the slope of the regression lines of buccal gape on total length differed significantly between the two types of predators (Figure 3), suggesting that divergence was beginning to occur at the maximum predator length tested.
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FIGURE 1.—Maximum prey sizes (X) consumed by striped bass and striped bass hybrids of various lengths (Y). Regression models were Y = 4.106 + 3.109X + 0.002X2, R2 = 0.88 for striped bass-redbelly tilapia; Y = - 263.442 + 8.406X - 0.029X2, R2 = 0.67 for striped bass-common carp; and Y= - 120.363 + 5.860X— 0.016X2, R2 = 0.92 for hybrid-redbelly tilapia.
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FIGURE 2.¾ Relation between total length (Y) and body depth (X) for redbelly tilapia and common carp. Regression models were Y = -2.512 + 3.321X, R2 = 0.98 for redbelly tilapia; and Y = -17.062 + 2.460X, R2 = 0.96 for common carp.
Striped bass ate longer common carp than they did redbelly tilapias, even though the girths of common carp exceeded those of redbelly tilapias of equivalent length. Perhaps this difference in selection may have resulted because common carp have only one dorsal spine to protect them from predation (Popova 1966) whereas redbelly tilapias have multiple spines. The propensity of hybrids to select larger redbelly tilapias than eaten by striped bass suggests that hybrids were more aggressive than striped bass (as Ware 1975 reported) or that the esophageal passage is less restricted in hybrid than in striped bass. Lawrence (1958) determined by dissection and from X-ray photographs that the cleithrum bones, which are rather inflexible structures, regulated the size of objects that could pass through the esophagus of largemouth bass. The X-ray images also indicated that the horizontal capacity of the esophagus was slightly larger than the vertical capacity. Regression analysis indicated that mouth width of largemouth bass was about 10% of total length for fish up to about 200 mm TL, 12% at 300 mm TL, and 13% or greater above 400 mm TL (Shireman et at. 1978).
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FIGURE 3.¾ Relation between buccal gape (Y) and total length (X) for striped bass and hybrid striped bass. Regression models were Y = -1.503 + 0.125X – 0.00005X2, R2 = 0.92 for stripped bass and Y = - 1.863 + 0.155X – 0.0001X2, R2 = 0.95 for hybrids.
In our study, striped bass ate redbelly tilapias no longer than 30% of their own lengths and common carp no longer than 44% of those lengths; hybrids ate redbelly tilapias up to 48% of their own length. We conclude that either redbelly tilapias or common carp provide suitable forage for striped bass and hybrids when the predators are large enough to eat the prey. Thus both striped bass and hybrids appear to be suitable predators for the control of common carp or tilapia offspring in polyculture.
Both prey species have been stocked in polyculture with striped bass and hybrids to control vegetation in ponds at Marion, Alabama, and to augment the standard pelleted-ration diet. The striped bass and hybrids harvested from ponds stocked with prey species were typically larger, more colorful, more robust, and more resistant to disease than were pond-reared fish fed only pelleted diets (N. C. Parker, unpublished data). We suspect that the improved condition of striped bass and hybrids feeding on omnivorous and herbivorous species is partially due to the presence of w -3 fatty acids and other essential nutrients obtained by the prey species from the aquatic plants on which they forage. Additionally, the presence of either redbelly tilapia or common carp reduced the amount of aquatic vegetation that frequently entangles striped bass and hybrids during harvest.
Redbelly tilapia may be the better of the two species to polyculture with striped bass and hybrids because tilapias do not survive temperatures much lower than about 9-15° C (Suffern 1980) and , therefore, would be easily separated from the Morone spp. If harvested during fall or winter in most of the USA. However, prohibition against the import of tilapias into some states (Shelton and Smitherman 1984) may make common carp the more widely acceptable prey species of choice.
We thank Robert R. Stickney, University of Washington, Seattle, Washington; Meryl Broussard, U.S. Department of Agriculture, Washington, D.C.; and two anonymous reviewers for providing constructive criticism of the manuscript.
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