Use of tropical cleaner fish to control the ectoparasite Neobenedenia melleni (Monogenea: Capsalidae) on seawater-cultured Florida red tilapia

Aquaculture, 113 ( 1993) 189-200 Elsevier Science Publishers B.V., Amsterdam

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AQUA 40054

Use of tropical cleaner fish to control the ectoparasite Neobenedenia melhi (Monogenea: Capsalidae) on seawater-cultured Florida red tilapia

Lauren E. CowelPb, Wade 0. Watanabea, William 13. Head”, Jill J. GrovePd and Jonathan M. ShenkePjb “Caribbean Marine Research Center, Vero Beach, FL, USA bDept. of Biological Sciences, Florida Institute of TechnoloNgy,Melbourne, FL, USA “Caribbean Marine Research Center, Lee Stocking Island, Exuma Cays, Bahamas ‘College of Oceanography, Oregon State University, HatJield Marine Science Center, Newport, OR, USA (Accepted 26 November

1992)

ABSTRACT

The juvenile bluehead wrasse (Thalassoma bifasciatum), the neon goby (Gobiosoma oceanops) and the cleaning goby (Gobiosoma genie) were evaluated for their abilities to remove ectoparasitic monogeneans (Neobenedenia melleni) from seawater-cultured Florida red tilapia. Initial and final infection levels (number of monogeneans/fish) were monitored -for individual tilapia maintained with and without cleaner fish in three g-day trials. Initial infection levels varied widely among trials, with averages ( + s.e.) of 4 12 k 103, 103 k 45 and 29 1 3~130 in trials 1, 2 and 3, respectively. Final infection levels on tilapia maintained without cleaners (controls) were significantly (P -=z0.05) higher than initial levels in trials 1 (148Ok 163), and 2 (275+50), but not in trial 3 (464+ 154). Although monogeneans were found in the guts of all three species of cleaners, at the end of each trial, the neon and cleaning gobies displayed superior cleaning abilities to the blulehead wrasse. Cleaning gobies reduced infection to 18.8, 1.1 and 41.2% of control levels, while neon gobies reduced infection to 27.8, 13.8 and 49.4% of control levels in trials 1, 2 and 3, respectively. Both goby species reduced infection to levels significantly (P < 0.017) below those of the controls in trials 1 and 2. Bluehead wrasse reduced infection to 47.0, 50.2 and 29.7% of the control levels in trials 1, 2 and 3; however, these differences were not significant (P > 0.05 ). The results demonstrate that cleaner fish, particularly the gobies, may be a viable biological method for controlling monogenean parasitosis in seawatercultured tilapia. Correspondence to: W.O. Watanabe, Vero Beach, FL 32963, USA.

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Marine Research

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INTRODUCTION

Several euryhaline species of tilapia and some interspecific hybrids have been shown to be suitable for culture in seawater (Liao and Chang, 1983; Stickney, 1986; Watanabe et al., 1988; Ernst et al., 1989; Watanabe, 199 1) . These tilapias are particularly desirable for use in arid coastal areas and islands where freshwater is limiting. A potential constraint to commercial culture of tilapias in seawater is susceptibility to infection by Neobenedenia melleni, a marine ectoparasite which has been reported to infect fish in over 20 different familes (Nigrelli and Breder, 1934; Nigrelli, 1937). IV. melleni has been found on tilapias grown in pools and ponds in the Bahamas (Ernst et al., 1989; Watanabe, 199 1 ), and in sea cages in Jamaica (Hall, 1990, 1992; Robinson et al., 1989)) Martinique (Gallet de Saint Aurin et al., 1990)) and Hawaii (Kaneko et al., 1988). The life history of N. melleni was described by Jahn and Kuhn ( 1932 ) . The hermaphroditic adults, ranging from 2 to 7 mm in length, attach to the sides, head and eyes of fish by means of a spined opisthaptor. They feed on mucus and epithelium, causing external hemorrhaging, and leading to secondary infection by bacteria, fungi or viruses (Robinson et al., 1992; Thoney and Hargis, 199 1) . In tilapia, early signs of infection include excess mucus production, cornea1 opacity and reduced feeding (Kaneko et al., 1988; Watanabe, 1991). Many chemicals have been employed as prophylactic and/or therapeutic agents for monogenean parasitosis in fish, including copper sulfate, formalin, potassium permanganate, trichlorfon, mebendazole and praziquantel (see Thoney and Hargis, 199 1 for review). Trichlorfon (Gallet de Saint Aurin et al., 1990) and formalin (Hall, 1990, 1992) have been used to treat N. melleni infection in seawater-cultured tilapia. Chemical treatments are often expensive to use on a large scale, and/or are not approved for use on food fish due to potentially harmful effects to consumers and to the environment. Treatments with fresh- or brackish water have been found effective in preventing and/or reducing parasitosis (Kaneko et al., 1988; Watanabe et al., in press), and are environmentally safe, but may be impractical on a commercial scale and/or with cage culture. As an alternative to chemicals and freshwater, cleaner fish may be used to control monogeneans and other ectoparasites on cultured fishes. In Norway and Scotland, temperate cleaner wrasses have been successfully used to control sea lice (Lepeophtheirus salmonis) infecting Atlantic salmon (Sdmo salar) grown in tanks and sea cages (Bjordal, 1988, 1990, 199 1). This method has been effective in reducing parasitosis on a commercial scale and is considered a realistic alternative to potentially dangerous chemical control methods (Bjordal, 1992; Costello and Bjordal, 1990). Cleaner fish have also been used

TROPICAL CLEANER FISH TO CONTROL ECTOPARASITES ON TILAPIA

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to control parasites in public display aquaria (D. Schleser, Dallas Aquarium, Dallas, TX, pers. commun., 199 1). The feasibility of using tropical cleaner fishes to control N melleni parasitosis in seawater-cultured tilapia has not yet been assessed. The objective of this study was to evaluate the abilities of three well-known tropical cleaner fishes, the juvenile bluehead wrasse ( Thalassoma bifasciatum), the neon goby ( Gobiosoma oceanops) and the cleaning goby (Gobiosoma genie) (Feddern, 1965; Bohlke and Chaplin, 1968; Darcy et al., 1974; Losey, 1974; Colin, 1975; Itzkowitz, 1979) to remove N. melleni from Florida red tilapia cultured in seawater. MATERIALS AND METHODS

The study was conducted at the Caribbean Marine Research Center (CMRC) on Lee Stocking Island (Exuma Cays, Bahamas) during April and May 199 1. The Florida red tilapia used in the study were descendants of an original cross between Oreochromis urolepis hornorum and 0. mossambicus (Behrends et al., 1982). Adult male tilapia (32.6 cm mean total length), sexreversed as fry (Guerrero, 1975 ), were raised in outdoor, flow-through seawater ponds ( 84 m3 ) , where they became infected with N. melleni. The experiment consisted of three identical trials. At the beginning of each trial, 24 tilapia were randomly selected for use in the experiment and 9- 10 additional fish were removed to determine initial infection levels (number of monogeneans per fish). To determine infection levels, individual tilapia were placed in black plastic buckets containing 10 1 of freshwater for a minimum of 10 min to kill the monogeneans. The fish were stroked to remove the monogeneans, which turned opaque in death. This process was repeated in a second bucket of freshwater to ensure the removal of all monogeneans. The water was then filtered through a 63-pm mesh sieve, and the collected monogeneans were preserved in 5% formalin. All sizes of monogeneans were counted. Juvenile bluehead wrasse.and cleaning gobies were collected from near shore reefs around Lee Stocking Island using quinaldine and dip nets. Neon gobies were purchased from a commercial hatchery (Aqualife Research Corporation, Walker’s Cay, Bahamas). Total lengths ranged from 15 to 25 mm (mean= 20.4 mm) for bluehead wrasse, 25 to 34 mm (mean= 28.7 mm) for neon gobies, and 24 to 38 mm (mean = 29.7 mm) for cleaning gobies. In each trial, individual tilapia were placed in glass aquaria ( 190 1) with two cleaner fish of the same species. Tilapia were also maintained without cleaners as a control. Twenty-four aquaria were used per trial, with six replicate aquaria per treatment. The cleaning abilities of the cleaner fish were evaluated by comparing final infection levels on tilapia kept with and without cleaners. The experimental tanks received flow-through seawater at an exchange rate

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of 11OO- 1200% day- ‘. They were covered with black plastic on all sides except the front to prevent visual interaction between fish in adjacent tanks. Light was supplied by a 20-watt fluorescent bulb located 3 1 cm above each tank, and a 12 h light: 12 h dark photoperiod was maintained. A PVC pipe ( 15 cm in length, 5.1 cm in diameter) was placed in each tank as a cleaning station and/or refuge for the cleaners. Cleaner fish which disappeared or died during the study were replaced. Tilapia were fed Zeigler tilapia chow (20% protein) once each afternoon to satiation. Ration was adjusted daily according to observed consumption and ranged from 0.2 to 0.8% body weight day- ‘. Uneaten food and waste matter were siphoned daily. Temperature, salinity and dissolved oxygen were measured daily in one tank from each treatment. Total ammonia-nitrogen, nitrite and pH were measured on the first, fourth and seventh days of each trial. No significant differences in water quality were observed among treatments for these parameters in any of the trials (ANOVA, P > 0.05). Water temperature ranged from 25.7 to 27.1 “C. Salinity was 38 ppt and dissolved oxygen ranged from 5.3 to 6.0 ppm during each trial. Mean pH ranged from 7.8 to 8.3, and mean NH4-N and NO*-N concentrations ranged from 0.02 to 0.07 ppm and 0.009 to 0.0 10 ppm, respectively. Initial and final infection levels on control tilapia were compared by analysis of variance. Final counts on tilapia in cleaner fish treatments were compared with final counts on controls in trials 1 and 3 using Fisher’s LSD test (Sokal and Rohlf, 198 1). Due to inequality of variances in trial 2, final counts on tilapia in cleaner fish treatments were compared with those on controls using the non-parametric Fligner-Policello test (Fligner and Policello, 198 I.; Day and Quinn, 1989). Because these comparisons were non-orthogonal, they were made using a conservative significance level of o? = 1.7%, according to the Dunn-Sidak method (Sokal and Rohlf, 198 1). Each tank was observed for 10 min per day, either between 08.00 and 11 .OO h or between 14.00 and 17.00 h. Schedules were varied so that each tank was observed at different times. Behavior of tilapia towards cleaner fish and aggressive and courtship behaviors within pairs of cleaners were noted. Numbers of aggressive chases were recorded. The Spearman rank correlation test was used to detect associations between behavioral data and monogenean count data (Siegel, 1956; Sokal and Rohlf, 198 1). The lengths of time that cleaner fish were observed on or inspecting tilapia were also recorded and were compared by analysis of variance followed by Fisher’s LSD test (Sokal andRohlf, 1981). At the end of each trial, cleaner fish were preserved and their gut contents analyzed in order to confirm the ingestion of monogeneans. Gut contents were analyzed in terms of percent frequency of occurrence of prey items and mean quantities of prey in non-empty guts.

193

TROPICAL CLEANER FISH TO CONTROL ECTOPARASITES ON TILAPIA

A group of cleaner fish separate from the experimental cleaners was observed cleaning tilapia and then immediately sacrificed. The duration of cleaning bouts was recorded and gut contents were examined to gain information on cleaning capacities. RESULTS

Pre- and post-treatment infection levels The initial mean number of monogeneans per fish varied considerably among trials, ranging from 103 in trial 2 to 4 12 in trial 1 (Table 1) . Final infection levels on tilapia maintained without cleaner fish (i.e., controls) reflected these relative differences in initial counts. The final counts on controls were significantly higher than initial counts in trials 1 (P < 0.001) and 2 (P < 0.05), but not in trial 3 (Table 1; Fig. 1). In trial 1, cleaning gobies and neon gobies reduced monogenean infection to levels which were significantly (P < 0.017) below those on the controls (Table 1; Fig. IA). The final mean counts on tilapia maintained with cleaning gobies and neon gobies were 18.8 and 27.8%, respectively, of the mean control count. Tilapia maintained with bluehead wrasse ended with a mean TABLE 1 Data on initial and final monogenean counts on tilapia maintained with and without (control) cleaner fish during three 8-day trials (see text for explanation). Data are presented as means k s.e. (no. of tilapia), with range in parentheses below. Means are also expressed as a percentage of the control. m = number of tilapia mortalities due to monogenean infection; r = number of cleaner fish replaced Monogenean Initial

counts (number per fish) Final Control

Bluehead wrasse

Neon goby

Cleaning goby

148Ok163 (5) (939-1938) ??Z=l

696+367(4) (190-1767) 47.0%

412f165(6) (4-981) 27.8%

278k 166 (6) (9-941) 18.8%

Trial 1

412+ 103 (9) ( 105-942)

m=2,r=l

2

103f45 (10) (22-490)

275+50 (6) ( 128-447)

138f43 (6) (23-318) 50.2% r=8

38+29 (6) (O-181) 13.8% r=l

3kl (O-7) 1.1% r=l

3

291+130(190) (8-1114)

464rf-154(6) (64-979)

138k68 (6) (24-460) 29.7%

229f103(6) (3-690) 49.4%

191k119 (l-700) 41.2%

r=4

r=l

r=2

(6)

(6)

Mean Number of Monogeneans Mean Number of Monogeneans

TROPICAL

CLEANER

FISH To CONTROL

ECTOPARASITES

ON TILAPIA

195

infection level which was 47% of that of the controls; this reduction was not significant. One tilapia in the control treatment and two in the bluehead wrasse treatment died during this trial as a result of severe monogenean infection. As was observed in trial 1, final monogenean counts on tilapia in trial 2 were significantly lower than control counts for cleaning gobies (P < 0.017) and neon gobies (P < 0.0 17 ), but not for bluehead wrasse (Table 1; Fig. 1B ) . Mean final counts on tilapia maintained with cleaner fish ranged from 1.1 to 50.2% of the mean control count. At the end of the trial, tilapia were completely free of monogeneans in one cleaning goby and two neon goby tanks. In trial 3, mean final infection levels on tilapia maintained with cleaners ranged from 29.7 to 49.4% of the mean control level (Table 1; Fig. 1C). However, as final monogenean counts varied widely within treatments (Table 1) , no significant reduction in infection level was achieved by any of the cleaner species. Behavioral observations Gobies readily approached tilapia, cleaning mainly over their sides and heads, and ingesting monogeneans with a rapid pulling and twisting motion. Tilapia were sometimes observed to remain motionless while being cleaned by gobies. In contrast, bluehead wrasse were more timid in approaching tilapia. The wrasse ingested monogeneans from the sides of tilapia in quick bites, but they were most frequently observed biting the ends of the tails or fins of the tilapia. Unlike the gobies, the bluehead wrasse frequently picked at particles on the tank bottoms. The cleaner fish adapted well to the aquarium environment, although there were some mortalities. Two bluehead wrasse died during the second trial and a total of 11 disappeared over the three trials. One neon goby died in each of trials 2 and 3. A gravid female cleaning goby was found dead at the end of trial 1 and a total of three disappeared. The tilapia were never observed to chase or attempt to ingest a cleaner fish. The average amount of time that pairs of cleaner fish were engaged in apparent cleaning behavior during 80 min of observation was significantly (P < 0.05) longer for cleaning gobies (34 + 5 min, n= 18 pairs) than for neon gobies (2 1 2 3 min, n = 18 ) and bluehead wrasse ( 17 -+2 min, n = 16 ) . Longer average cleaning times were significantly associated with lower final monogenean counts for cleaning gobies and bluehead wrasse (P < 0.05 ), but not for neon gobies. Aggressive interactions were observed between cleaner fish during the study. Chases were most frequent and most severe between pairs of neon gobies, and infrequent between bluehead wrasse (see Cowell, 1991). Dominant gobies often chased subordinates from the tilapia and did the majority of the cleaning. However, numbers of chases and final monogenean counts were not cor-

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L.E. COWELL ET AL.

related for any species of cleaner (P > 0.05 ) . Two neon gobies may have died as a result of frequent aggressive interactions. Three pairs of neon gobies and one pair of cleaning gobies exhibited behaviors associated with courtship, including nudging, chasing and swimming in circles around one another (Feddern, 1967; Colin, 1975; Thresher, 1980). One pair of neon gobies which were almost always observed in courtship activities was seen cleaning for only 1 of 80 min of observation time. The tilapia with them had the highest final infection level ( 18 1) of those kept with neon gobies in trial 2. Gut con tent analyses At the termination of the trials, three types of evidence of cleaning behavior were observed in the guts of all three cleaner species: whole monogeneans, opisthaptor hooks and monogenean eggs (Table 2). Whole monogeneans were ingested most frequently by cleaning gobies, and eggs were ingested most frequently by bluehead wrasse. More bluehead wrasse demonstrated recent cleaning behavior (containing either monogeneans, hooks or eggs) than did either species of goby. However, this was not indicative of overall cleaning performance, because all of the neon gobies and all but two of the cleaning gobies which lacked gut-content evidence of cleaning behavior were taken from tanks in which the tilapia had low ( < 50) final infection levels. All three species of cleaner fish ingested alternate prey items: small zooplankters, primarily copepods (Table 2). Bluehead wrasse ingested alternate prey more frequently than did either species of goby. TABLE 2 Gut contents of cleaner fish at the ends of trials. Data shown are results from all three trials combined. % FO= (no. of non-empty fish containing a prey item/no. non-empty fish) X 100. x=total no. of a prey item found in all non-empty fish/no. of non-empty fish Prey item

Whole monogeneans Opisthaptor hook sets Monogenean eggs Monogeneans, hooks or eggs Any alternate prey items

Bluehead wrasse (n=29)”

Neon goby (n=36)

Cleaning goby (n=29)”

%FO x*s.e. %FO xfs.e. % FO x? s.e.

3.4 0.03 f0.03 58.6 0.66kO.12 72.4 5.86+ 1.95

8.3 0.14f0.09 52.8 0.94 f 0.20 55.6 7.50f 2.35

13.8 0.31 kO.16 17.2 0.21 f 0.09 34.5 1.41 kO.61

%FO

86.2%

66.7%

44.8%

O/oFO

93.1

52.8

51.7

“Three bluehead wrasse were lost at the ends of trials. ?Seven cleaning gobies had empty guts.

TROPICAL CLEANER FISH TO CONTROL ECTOPARASITES ON TILAPIA

197

In the separate set of cleaner fish which were sacrificed immediately after they were observed cleaning, an average of 13.8 ? 3.4 whole monogeneans were found in the guts of cleaning gobies (y1= 12)) compared with 1.7 + 0.6 in neon gobies (II = 10) and 3.4 t 1.4 in bluehead wrasse (y1= 11) . The lengths of time for which cleaners were observed on tilapia were 13.4 -t 2.3 min for cleaning gobies, 7.4 + 2.0 min for neon gobies and 5.4 -t 1.1 min for bluehead wrasse. The best performance was given by a cleaning goby that had ingested 4 1 monogeneans during 2 5 min of cleaning. DISCUSSION

The results of this study demonstrate that juvenile bluehead wrasse and adult neon and cleaning gobies ingest N. melleni from infected seawater-cultured tilapia, but indicate that the gobies are much more effective at reducing infection levels than are the wrasse. That cleaning gobies were highly effective at removing monogeneans is suggested by a comparison of the final infection levels on tilapia kept with them and the control levels in trial 1, and by the quantities of whole monogeneans found in individual cleaning gobies following cleaning activity. While high initial infection levels probably contributed to relatively high final monogenean counts in trial 1, nearly complete removal of monogeneans by cleaning gobies was observed when initial infection levels were moderate, as in trial 2. This suggests that cleaning gobies are capable of eliminating monogeneans from fish with light to moderate infections in a short period of time. Neon gobies were also effective at removing monogeneans from tilapia, and, like cleaning gobies, reduced infection to very low levels in trial 2 when initial infection levels were moderate. The cleaning performance of the neon gobies is especially noteworthy, given that they were aquariumraised and unaccustomed to symbiotic cleaning. A number of factors may have limited the cleaning efficiency of the bluehead wrasse. In the wild, bluehead wrasse do not have prolonged periods of contact with hosts or pursue hosts that do not invite cleaning (Losey, 1974). The timidity shown by many of the wrasse towards the tilapia is consistent with this observation. Feeding strategies and cleaning behaviors of bluehead wrasse are related to their social grouping, which is affected by physical factors such as reef structure and depth (Itzkowitz, 1979). Furthermore, the wrasse are facultative cleaners (Feddern, 1965; Itzkowitz, 1979) and consumed more planktonic foods than did the gobies. Results of this study suggest that, unlike neon or cleaning gobies, bluehead wrasse are not capable of rapidly reducing or eliminating monogenean populations on infected tilapia. Although the tilapia did not pose for cleaners, as is characteristic of fish being cleaned in the wild (Losey, 197 1, 1972)) they tolerated cleaning. Because many freshwater cichlids are known to act as hosts to cleaner fish (Wyman and Ward, 1972; Minshull, 1985; Stauffer, 199 1) and repeated tactile

198

L.E. COWELL ET AL.

stimulation by cleaners may induce posing behavior in hosts (Losey, 1972)) it is conceivable that the tilapia could learn to solicit cleaning. Although tilapia were never seen to pursue the cleaners, it is presumed that the cleaners which disappeared during the study were ingested when they were dead or moribund. Tilapia were observed ingesting dead cleaners in preliminary experiments (Grover, unpubl. obs. ) . Although a lack of correlation between aggressive behavior (i.e. frequency of chases) and final monogenean counts suggests that intraspecific aggression did not reduce cleaning efficiency of any cleaner species, mortalities of neon gobies may have resulted from such aggression. The replacement of dead or missing cleaner fish during the study probably minimized the potentially inhibitory effects of intraspecific aggression on cleaning efficiency. Courtship behavior appeared to reduce greatly the cleaning efficiency of one pair of neon gobies in trial 2. The widespread use of cleaner fish for control of ectoparasites on cultured fish will be dependent on their availability. Many members of the genus Gobiosoma are easy to spawn and rear in captivity (Colin, 1975; Thresher, 1980). Techniques for raising neon gobies are well established (Moe, 1975; Walker, 1977), and they are currently being produced commercially (G. Waugh, Aqualife Research Corporation, Walker’s Cay, Bahamas, pers. commun., 1991). Bluehead wrasse have not yet been successfully reared in captivity (G.J. Holt, University of Texas, Port Aransas, TX, pers. commun., 1992). Given their effectiveness in removing N. melleni and their suitability for artificial propagation, it is recommended that neon and cleaning gobies are used for future studies on control of monogenean parasitosis in seawater-cultured tilapia. These studies should determine the ratios of cleaners to tilapia required to prevent infection of non-parasitized fish and to eliminate monogeneans from lightly to moderately infected fish. Long-term experiments conducted in larger culture units, with larger numbers of tilapia and cleaners, are needed to evaluate the practicality of this method. The cost of supplying and maintaining the cleaners, their possible predation by tilapia, and the effect of their presence on harvesting procedures must also be evaluated. The results of this study suggest that further experiments using tropical cleaner fish to control N. melleni or other ectoparasites on various marine fishes in captivity are warranted, The ecological consequences of using nonnative cleaner species should be considered. ACKNOWLEDGEMENTS

We thank Karl Mueller, Simon and Eileen Ellis, Leland and Lori Cain, Javier Ruiz, Sheri Hall, Ricky Riera-Gomez, Ed Wishinski, Dennis Thoney and Stuart Schell for technical assistance, and Allan Stoner, Godfrey Waugh and Robert Wicklund for helpful advice. This project was supported by a grant

TROPICAL CLEANER FISH TO CONTROL ECTOPARASITES ON TILAPIA

199

from the National Undersea Research Program, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, by the Perry Foundation, Inc., and by the Florida Institute of Technology.

REFERENCES Behrends, L.L., Nelson, R.G., Smitherman, R.O. and Stone, N.M., 1982. Breeding and culture of the red-gold color phase of tilapia. J. World. Maricult. Sot., 13: 2 1O-220. Bjordal, A., 1988. Cleaning symbiosis between wrasses (Labridae) and lice infested salmon (Sulmo s&r) in mariculture. Int. Count. Explor. Sea, C.M. F: 17,s pp. Bjordal, A., 1990. Sea lice infestation on farmed salmon: possible use of cleaner-fish as an alternative method for de-lousing. Can. Tech. Rep. Fish. Aquat. Sci., 1761: 85-89. Bjordal, A., 199 I. Wrasse as cleaner-fish for farmed salmon. Prog. Underwater Sci., 16: 17-28. Bjordal, A., 1992. Cleaning symbiosis as an alternative to chemical control of sea lice infestations of Atlantic salmon. In: J.E. Thorpe and F.A. Huntingford (Editors), The Importance of Feeding Behaviour for the Efficient Culture of Salmonid Fishes. Papers presented at World Aquaculture 90, Halifax, Nova Scotia, 12 June 1990. World Aquaculture Workshops, Number 2. World Aquaculture Society, Baton Rouge, LA, pp. 235-26 1. Bohlke, J.E. and Chaplin, C.C.G., 1968. Fishes of the Bahamas and Adjacent Tropical Waters. Livingston Publishing Company, Wynnewood, PA, 77 1 pp. Cohn, P., 1975. The neon gobies. T.F.H. Publications, Inc., Neptune City, NJ, 304 pp. Costello, M. and Bjordal, A., 1990. Biological control of sea lice on caged salmon. Fish Farmer, 13(3): 44-46. Cowell, L.E., 199 1. Use of tropical cleaner fish to control the ectoparasite Neobenedenia melieni (Mongenea: Capsalidae) on saltwater Florida red tilapia. MS. Thesis, Florida Institute of Technology, FL, 46 pp. Darcy, G.H., Maisel, E. and Ogden, J.C., 1974. Cleaning preferences of the gobies Gobiosoma evelynae and G. prochilos and the juvenile wrasse Thalassoma bifasciatum. Copeia, 1974: 375-379. Day, R.W. and Quinn, G.P., 1989. Comparisons of treatments after an analysis of variance in ecology. Ecol. Monogr., 59: 433-463. Ernst, D.H., Ellingson, L.J., Olla, B.L., Wicklund, R.I., Watanabe, W.O. and Grover, J.J., 1989. Production of Florida red tilapia in seawater pools: nursery rearing with chicken manure and growout with prepared feed. Aquaculture, 80: 247-260. Feddern, H.A., 1965. The spawning, growth, and general behavior of the bluehead wrasse, Thalassoma bifusciatum (Pisces: Labridae). Bull. Mar. Sci., 15: 896-941. Feddern, H.A., 1967. Larval development of the neon goby, Elactinus oceanops, in Florida. Bull. Mar. Sci., 17: 367-375. Fligner, M.A. and Policello, G.E., 198 1. Robust rank procedures for the Behrens-Fisher problem. J. Am. Stat. Assoc., 76: 162-168. Gallet de Saint Aurin, D., Raymond, J.C. and Vianas, V., 1990. Marine finfish pathology: specific problems and research in the French West Indies. Advances in Tropical Aquaculture. Tahiti, 20 February-March 1989. AQUACOP IFREMER, Actes de Colloque, 9: 143- 160. Guerrero III, R.D., 1975. Use of androgens for the production of all-male Tilupia aurea (Steindachner). Trans. Am. Fish. Sot., 104: 342-348. Hall, R.N., 1990. The mariculture potential of two strains of tilapia in Jamaica. MPhil. Thesis, Univ. West Indies, Mona, Kingston, Jamaica, 175 pp. Hall, R.N., 1992, Preliminary investigations of marine cage culture of red hybrid tilapia in Jamaica (Abstract). Proc. Gulf Carib. Fish. Inst., 42: 448.

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