Development of Nursery Systems for Black Sea Bass Centropristis striata

Vol. 34, No. 3 September, 2003

JOURNALOFTHE WORLD AQUACULTURE SOCIETY

Development of Nursery Systems for Black Sea Bass Centropristis striata KEVIN

R.

STUART A N D

THEODORE 1.J. SMITH

Marine Resources Research Institute, South Carolina Department of Natural Resources, 21 7 Fort Johnson Rd., Charleston, South Carolina 29412

Abstract Black sea bass (Centropristis striatu) are territorial fish and cannibalism is a concern when rearing juveniles in intensive systems. Three studies were conducted to provide information for development of suitable tank nursery systems for juvenile black sea bass (3.6-4.5 cm; 0.8-1.7 8). Studies were performed a t the Marine Resources Research Institute, Charleston, SC, using 1.5-m diameter X 0.8 m deep tanks connected to recirculating seawater systems. The studies examined growth and survival a t different stocking densities, selection and utilization of habitats, and, effects of water velocity on positioning and movement of fish. In study 1, fish were stocked at biomass densities of 126.7, 253.3, and 506.7 g/m3 and reared for 56 days with no habitats. No difference in growth was detected although fish reared a t the lower densities had significantly lower mortality (mean 7.9%) as compared to those a t the highest density (28.0%). At the highest density, cannibalism appeared to be a substantial cause of mortality. In study 2, three habitat types were used, (1)two-tier structure constructed from plastic grating with 15 mm square openings (volume = 0.015 m3); (2) PVC pipe bundle (volume = 0.004 m3); (3) rock aggregate (volume = 0.008 m3). Of the habitats, the most utilized habitat (62.9%) was the two-tier layered structure that allowed movement in all directions. The next utilized type was the pipe bundle (25.6%) with the openings inhabited by the largest juveniles in each tank. Overall, a mean of 18.2% of the fish were observed using habitats. Study 3 examined water velocities ranging from 0.01 to 0.12 d s e c . Most fish became concentrated in the tank bottom area having a water velocity in the range of 0.040.09 d s e c . At these velocities there were few aggressive interactions. Smaller fish inhabited the areas outside this velocity range. At the higher velocities, the small fish swam vigorously to maintain their position in the water column. At the low velocities, sporadic incursions of larger fish occurred presumably to attempt to cannibalize or to defend territory. Results from these studies help to define characteristics of nursery systems for rearing juvenile black sea bass.

Black sea bass (Cenfropristisstriatu) occur along the Atlantic coast from the Gulf of Maine to Northern Florida and in the Gulf of Mexico (Miller 1959; Musick and Mercer 1977; Able and Hales 1997). Throughout its range this species supports both recreational and commercial fisheries (Huntsman 1976; Musick and Mercer 1977; Low 1981). The value of fillets has increased in recent years, selling for an average wholesale price of $2.75 to $3.30/kg. Also, live fish (0.9 to 1.1 kg) are sold in the American and Canadian sushi markets at $7.72 to $9.92/kg (Walker and Moroney 2000). Captive spawning of black sea bass was first reported in 1884 using fish caught off

the coast of South Carolina (Earl1 1884). Shortly thereafter, Wilson ( 1889) captured and spawned sexually mature fish caught off of the coast of Massachusetts. Since then, black sea bass from the Atlantic coast have been induced to ovulate (tank and strip spawning) using human chorionic gonadotropin (HCG) (Hettler and Clements 1978; Cerda et al. 1996) and LHRHa (Berlinsky et al. 2000; Watanabe et al., in press). During recent years, there has been increasing interest in black sea bass as an aquaculture candidate due to its high market price and the ability to control reproduction (Roberts et al. 1976; Tucker 1989). Limited information on the environmental tolerance of juveniles is now available (At-

0 Copyright by the World Aquaculture Society 2003

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wood et al. 2001, in press; Berlinsky et al. 2000), however additional information is needed to develop commercial scale nursery systems. Black sea bass are considered hardy and gregarious, but they are also highly territorial and cannibalistic (Gwak 2002). Thus, identification of specific rearing conditions is necessary to design efficient culture systems. Three tank studies were performed in Charleston, South Carolina at the Marine Resources Research Institute (MRRI) to identify suitable conditions for use in tank nursery systems for juvenile black sea bass. These studies examined: the effect of stocking density on growth and survival: selection and utilization of natural and artificial habitats; and, effect of water velocity on positioning and movement.

Materials and Methods Juvenile black sea bass were produced from 90 adults collected off the coast of Norfolk, Virginia. Broodstock were naturally (volitional) and hormonally spawned (LHRHa implants). Larvae were reared at Southland Fisheries Corporation (SFC), Edisto, South Carolina, until the Juvenile stage (mean weight = 0.2 g) at which time they were transferred to MRRI. The studies were performed using two rows of 4 fiberglass tanks (1.56 m diameter X 0.80 m deep, water volume 1500 L), with each row containing three experimental tanks and a filter reservoir tank. Each row of tanks was connected to a separate recirculating seawater system. Fish were exposed to ambient room temperatures (23-25 C) and a combination of fluorescent and natural (through building windows) lighting. Water quality was monitored weekly in the reservoir tanks during each study. Dissolved oxygen (DO) concentration and temperature were measured with a meter (YSI model 57, Yellow Springs Instruments Inc., Yellow Springs, Ohio, USA). Lamotte Octet Comparator test kits (Lamotte Chemical Co. Chestertown, Maryland, USA) were used to measure pH (model p5100) and to-

tal ammonia nitrogen (model PAN). Salinity was measured with a refractometer (Spartan Refractometers, Japan). Feces and uneaten food were removed daily by siphoning to help maintain satisfactory water quality conditions. Fish were fed a 3 mm sinking pellet (38% protein, 8% lipid, Zeigler Bros, Gardners, Pennsylvania, USA) at a rate of approximately 5% body weight/ day. Feed was provided throughout the day using 12-hr automatic belt feeders (Aquatic Ecosystems, Apopka, Florida, USA). Fish were assigned randomly to each treatment replicate. Statistical analysis of fish size at stocking indicated there were no differences among treatments within a study (P > 0.05). In study 1, juveniles (mean TL of 3.6 t 1.4 cm; mean weight of 0.8 2 0.2 g) were stocked in replicate tanks without habitats at three biomass densities; 126.7, 253.3, and 506.7 g/m3 (250, 500 and 1,000 fish/ tank, respectively). Fish were weighed and measured weekly (20 fishhank) over the 56d study period. During each sample, all fish were also counted to determine mortality. Fish were observed daily and dead fish were removed and examined. Mortality was classified as due to either natural causes or cannibalism. Natural mortality was defined as “dead on the bottom” with no signs of cannibalism. Cannibalism was classified as either a missing fish, an observation of fish eating fish, or a partially eaten fish on the bottom. Classifying mortality was subjective, as it was possible that mortality classified as natural could have been caused by agonistic behavior while mortalities classified as cannibalism could have been due to damage that occurred after natural mortality. However, this approach was considered useful for general interpretation of the mortality data. In study 2, fish utilization of three types of habitats was examined over a 28-d period. Habitat types consisted of (1) a twotier structure constructed with shelves of plastic grating having 15 mm square openings (volume = 0.015 m3); (2) tube open-

NURSERY SYSTEMS FOR BLACK SEA BASS

ings made from PVC pipe (volume = 0.004 m3); and, (3) a rock aggregate (volume = 0.008 m3) (Fig. 1). Each of the six test tanks contained each habitat type evenly spaced o n the bottom (six replicateshabitat type). Each habitat was placed in a different location in the tanks to minimize external influences o n usage. A total of 600 juveniles (4.2 5 1.8 cm TL; 1.4 2 0.4 g) were randomly placed in the six tanks (100 fish/ tank, 212.1 g/m3). The fish as well as the habitats were placed into the tanks at approximately the same time and fish were allowed to acclimate for 24 h before data were collected. Observations were taken twice daily over 28 d with a Nikon CoolPix 950 digital camera (Nikon Inc., Japan), for a total of 56 observations. Habitat usage was reported as the percentage of all fish in a tank using any type of habitat (use defined as being on, underneath or within the structure, or within approximately 1 body length distance of a structure). Habitat preference was quantified as percent of fish using a particular habitat type relative to the total number of fish using all habitat types. In study 3, the effect of water velocity on positioning and movement of juveniles (4.5 ? 1.3 cm TL; 1.7 ? 0.6 g) was examined in each of the six tanks without habitats by recording behavior of fish (100 fiswtank; 257.6 g/m') utilizing different tank areas with different water velocities. Water velocity was maintained in each tank by keeping water inflow volume and injection angle approximately the same. Maximum bottom water velocity occurred downstream from the injection point and then decreased around the tank. Velocity ( d s e c ) was measured across the tank bottom using a flow meter (Flow Velocity Meter, Model PVM2, Montedoro Whitney Inc.). The different water velocity zones were identified by marks on the lip on the top wall of each tank. Water velocity was also recorded by depth and distance from tank periphery and found to correspond closely with bottom measurements. Observations were taken twice daily over a 21-day period with a Ni-

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kon CoolPix 950 digital camera. Analysis of the digital image was used to determine occurrence of fish in different velocity zones. Parametric statistics (ANOVA) were used to compare water quality parameters. However, non-parametric analysis was used in all other comparisons as the data failed to meet the requirements of normality and or homogeneity of variance. Length and weight data were analyzed by Kruskal-Wallis one way ANOVA (Sigma Stat, Jandel Scientific software, San Rafael, California, USA), All percent data were arcsine square root transformed and then Kruskal-Wallis one way ANOVA was performed (Sigma Stat, Jandel Scientific software, San Rafael, CA). Differences were considered significant at P < 0.05.

Results and Discussion There were no differences (P = 0.099) in water quality parameters measured in the two tank systems used during each study (Table 1). Mean temperature ranged from 22.5 to 23.5 C and salinity ranged from 32 to 34 ppt. The water conditions maintained during the studies were within known acceptable levels for culture of black sea bass (Atwood et al. 2001) and no mortality was directly attributable to unsatisfactory water quality. Analysis of final size data in study 1 indicated that there were no significant differences ( P = 0.067) in final length or weight associated with the different densities (126.7, 253.3, and 506.7 g/m3). However, the larger fish occurred in the highest density (506.7 g/m3) and the greatest mortality (28%) was also recorded in this treatment (Table 2). It appeared that the high degree of mortality was related to cannibalism and this may explain the occurrence of larger fish in this treatment at conclusion of the study, as the smaller fish may have been eaten. There was no significant difference in mortality between the low and medium density tanks (8.0 and 7.8%, respectively) and few aggressive interactions were

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A

C

FIGURE 1.

Schematic drawings of habitat types used to evaluate habitat preference by juvenile black sea bass. A-Two-tier horizontal structure, B-PVC pipe bundle, C-Rock aggregate.

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Mean 2 SD water qualify values measured during the nursery studies. There were no signijicant differences (P 2 0.05) among replicates within each study.

TABLE 1.

Stocking density Habitat use Water velocity

23.5 2 1.5 22.5 2 2.3 23.0 2 1.7

34 ? 1.0 34 2 1.0 32 ? 1.5

7.06 2 2.3 6.98 2 3.1 6.91 2 1.9

0.3

?

0.5

0.4 2 0.6

0.4 2 0.3

8.0 2 0.5 7.5 2 1.0 8.0 2 0.8

noted in these treatments (Table 2). The ef- (3,200 g/m3) was six fold greater than that fect of stocking density on survival and examined with the black sea bass and over growth has been examined in a number of nine times greater than the lowest density species including, sea bream (S. uurutu L.), group (253.3 g/m3) tested. Lastly, differenarctic charr (Sulvelinus ulpinus L.), Nassau tial mortality may have been the cause as grouper (Epinephelus sulmoides), and rain- density did have a measurable impact on bow trout (Oncorhynchus mykiss) (Chua survival with the smaller fish becoming apand Ten 1979; Baker and Ayles 1990; Bag- parent prey of the larger fish. Further, canley et al. 1994; Canario et al. 1998). Stock- nibalism of smaller fish by larger fish may ing and rearing density affect such factors be more prevalent in a population where as growth, mortality, water quality, feeding, there is wide variance in sizes, especially at and grading (Wallace and Kolbeinshavn high density (Sowka and Brunkow 1999). 1988; Canario et al. 1998; Sowka and Brun- This may have been the case in the present kow 1999). Typically, social interactions study as there was a wide range of fish sizes and competition for food or space result in at time of stocking. Grading by fish size is an inverse relationship between growth and commonly practiced in aquaculture and it density (Purdom 1974; Jobling 1985; Can- has been shown to result in increased ario et al. 1998). However, this relationship growth rates by eliminating the possibility was not observed in the present study. for a social hierarchy based on size (Gunnes There are several possible explanations 1976; Wallace and Kolbeinshavn 1988). which might explain the lack of density im- Food, feeding frequency, and feed quality pacts on growth. First, perhaps study du- are also factors that affect both stocking ration was insufficient for differences in density and the degree of cannibalism (Walgrowth to be manifested. Second, the high lace and Kolbeinshavn 1988). Although stocking density (506.7 g/m3) selected in continuous delivery belt feeders, which the study may be below the threshold that provided feed throughout a 12-h period, results in a density dependent interaction. were used in the study, the food may not For example, Canario et al. (1998) reported have met the nutritional and or behavioral 25% slower growth with sea bream reared requirements of these fish. However, as canat the highest density tested but this density nibalism was nominal at the lower densiTABLE 2. Data ut conclusion of study I (day 5 6 ) exumining the efsects of stocking density on growth (mean 2 SD) and survival of black sea bass. Data in columns followed by different superscripts were significantly different (P < 0.05).

Fish size

Mortality (%)

Density (g/m7)

TL (cm)

WT ( g )

Cannibalism

Natural

Total

126.7 253.3 506.7

4.11 5 0.9.' 4.23 ? 1 . 1 " 4.78 ? 0.4'

1.22 ? 0.3' 1.31 2 0.98 1.68 2 1.0'

2.0 2 0.7a 3.0 ? 0.4" 21.0 ? 5.7h

6.0 2 0.8' 4.8 2 0.3a 7.0 t 1.1.'

8.0 2 1.2' 7.8 2 0.7.' 28.0 2 8.1h

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TABLE3. Data (mean 2 SD) on survival and habitat utilization by juvenile black sea bass exposed to three hubitat types. Percent data reported by habitat rype reflect the utilization relative to fish using habitats. while total use reflects the percent of all$sh in the tank utilizing any type of habitat. Data in columns or rows with different superscripts were significantly different ( H = 216.18: P < 0.001). Fish data

Tank no.

I 2 3 4 5 6 Mean

TL (cm)

4.4 5 4.6 t 4.5 5 4.4 2 4.6 5 4.5 5 4.5 ?

0.5 0.3 0.3 0.6 0.6 0.4 0.6

Habitat utilization (%)

WT (g)

Mortality (%)

Horizontal layers

1.5 2 0.4 1.8 5 1.0 1.7 -+ 1.1 1.8 -+ 0.5 1.9 ? 0.5 1.6 t 0.6 1.7 t 0.8

9.0 7.0 6.0 4.0 3.0 5.0 5.7 ? 2.3

65.6 t 2.1" 58.3 t 4.8" 57.4 t 3.3a 65.5 t 1.8" 65.6 t 3.8' 65.1 ? 2.7' 62.9 t 3.1"

ties, feed type and availability factors do not appear to be major issues (Table 2). The use of suitable artificial habitats may allow increased rearing densities without a concomitant increase in mortality or decreased growth. Proper structure may give small fish and the slower growers in a population protection while also offering the production of more uniformed sized groups of fish (Potts and Hulbert 1994; Gwak 2002). Under natural conditions, many fish species tend to congregate in pronounced areas of topographical relief on the sea bottom (Mottet 1985). Reefs and hard bottom rock outcrops provide such topographical relief and attract large numbers of fishes. Typically, the higher complexity of the natural or artificial habitat, the greater number of fishes that will live in and on it (Randall 1963; Potts and Hulbert 1994). In study 2, there was selection among the different habitats by the juvenile black sea bass. The horizontal layer unit was the most utilized habitat type (62.9%) followed by the tube openings (25.6%) and rock aggregate (1 1.5%) (Table 3). Overall, an average of 18.2% of fish used the habitats. Mean mortality during this 28-d study was 5.7%. Even though habitat usage was relatively low (18.2%) the total amount of the tank volume occupied by the habitats was only (2.0%), showing that the fish did select for the habitats over the open water in the tank. The horizontally layered structure provided

Tube openings

24.2 ? 26.2 ? 28.4 ? 25.0 ? 23.8 -C 25.8 2 25.6 2

2.3h I.Ib 5.3h 2.2h 2.gh l.gh 2.6h

Rock aggregate

Total use

10.2 ? 15.5 t 14.2 2 9.4 t 10.6 ? 9.1 t

1.4' 18.9 t 1.9 2.2' 18.4 ? 2.6 1.3c 18.1 t 1.8 1.0' 17.7 2 2.9 1.8' 17.5 t 1.8 2.Ic 18.5 t 1.7 11.5 2 1.6= 18.2 t 0.5

large open areas and some protection due to the nature of the structure. However, the open-ended tube structure attracted the largest fish in each tank and appeared to be the preferred structure for these fish. The low number of holes (3 on each end) may have restricted the number of fish, which could use these tubes to those, which could best defend it. Other studies have also shown that hole diameter does elicit fish size selection with smaller fish preferring small holes and larger fish utilizing larger holes (Kellison and Sedberry 1998). This was also observed with wild Nassau grouper, E. striatus, where larger individuals tended to be more abundant on large-hole reefs where they often occupied individual holes (Beets and Hixon 1994). Since many reef fish including black sea bass settle out as post-larvae on coral clumps, subtidal estuarine habitats, and rocky bottoms (D'Anna et al. 1994; Eggleston 1995; Able and Hales 1997), artificial habitats containing small openings could be useful as nursery areas and may also serve as 'recruitment reef structures'. For aquaculture purposes, an efficient early nursery design might consist of a multi-level unit containing a variety of holes sizes to accommodate different sizes of fish and to allow for some differential growth. However, inherent issues associated with use of intank structures typically include fouling and increased sedimentation, which may require

NURSERY SYSTEMS FOR BLACK SEA BASS

TABLE 4. Percent occurrence (mean 2 S D ) of black seu bass in different wafer velncities. Data in columns with different superscripts were signijicantl-v different (P 5 0.025). Velocity (dsec)

Occurrence

0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

2.0 t 1.1" 8.0 t 2.3a 11.0 L ] . O h 13.0 2 I S h 11.0 2 3 3 13.0 2 2.4h 11.0 C 1.3h 11.0 ? 1.8h 6.0 2 l.6n 4.0 ? 0.P 4.0 ? 1.1:' 4.0 ? 1.8' 2.0 ? 0.5"

0.1 1 0.12 0.13 0.14

(%)

additional cleaning to prevent water quality problems. A bio-economical compromise might be to restrict habitat deployment to only the early stages where cannibalism is high. It has been shown that moderate swimming exercise improves growth, flesh quality, swimming ability, and physiological and biochemical traits of several species of fish (Ogata and Oku 2000). Further, under natural conditions, water velocity is a crucial factor as it directly affects survival (e.g., habitat selection, feeding ability, predator avoidance, etc.). In culture systems, water velocity affects factors such as physiological condition, oxygen consumption, and feed utilization, all of which have biological and economic implications. In study 3, it was apparent that juvenile black sea bass displayed a preference for certain velocities. The majority (70.0%) of fish swam to maintain position and equal spacing from other fish within velocities of 0.04 and 0.09 d s e c (Table 4). Analysis of the positioning data indicated that there were no differences in positioning within this range (0.04 to 0.09 d s e c ) . However, velocities slower than 0.04 d s e c and faster than 0.09 d s e c were less preferred (Table 4). The smaller fish in each tank were ob-

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served at the faster (0.10-0.14 d s e c ) and slower velocities (0.02-0.03 d s e c ) . Further, observations indicated that these fish in the less preferred zones did not attempt to move into the more preferred areas. In contrast, larger fish in the periphery of preferred velocity zones would often dart into less preferred low velocity areas causing rapid dispersion of fish in the area. It is not known if these incursions were attempts at cannibalism (none observed) or perhaps related to territoriality. Mean mortality during this 21-d study was 10.6%. These studies provide information useful in the development of nursery systems for juvenile black sea bass. Future work should consider the effects of tank size as well as the behavior of different size juveniles. Research on evaluation of more complex habitat types and effects of a broader range of culture densities would also be beneficial.

Acknowledgments We thank Southland Fisheries Corporation for providing the juvenile black sea bass used in the studies. Louis Heyward and Charles Bridgham assisted in sampling and lab maintenance. Mike Denson provided input of the experimental design. Karen Swanson prepared the figure. Wallace Jenkins, Mark Collins, and Mike Denson provided constructive review of the manuscript. This study was funded by grant NAI6RG 1561 from the National Marine Aquaculture Initiative of the National Oceanic and Atmospheric Administration, administered by the South Carolina Sea Grant Consortium, and the SC Department of Natural Resources. This is contribution number 5 17 of the South Carolina Marine Resources Division.

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