salinity tolerance of introduced south american sailfin...

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Philippine Journal of Science142 (1): 13-19, June 2013ISSN 0031 - 7683Date Received: ?? Feb 20??

Key Words: janitor fish, Pasig River, Pterygoplichthys, salinity tolerance

*Corresponding author: [email protected]

Marco Alberto Brion, Jose Gil Guillermo Jr, Cheston Uy, Joel Chavez, and Jose Santos Carandang IV*

Biology Department, De La Salle University-Manila 2401 Taft Avenue, Manila, Philippines

The ecological distribution of species is limited by its physiological tolerances towards natural physical barriers. The experimental LC50 of salinity to an introduced freshwater fish was determined as it implies to its dispersal and distribution. South American sailfin catfishes belong to a freshwater fish family but introduced specimens have been collected in brackish waters of the Pasig River in the Philippines. Tolerance to salinity of this introduced fish could mean increased potential to expand its range into or via marine waters. Juvenile South American sailfin catfishes were purchased from local petshops and were subjected to a 96-hour toxicity test for salinity in the laboratory. Replicated tests using various salinity concentrations were performed. Mortality and survival of test samples were tabulated to determine LC50.The LC50 of salinity was calculated to be 10.6 g/L. Survival analysis of the data gives an estimate that at 10 g/L concentration over 50% of the samples have strong chance of survival beyond 85 hours of exposure to saline water. Post mortem identification of samples confirms they belong to genus Pterygoplichthys. We discuss the implications of the LC50 results on the migration and dispersal of this introduced freshwater fish, and the application of taxonomic data in the study of invasions.

Salinity Tolerance of Introduced South American Sailfin Catfishes (Loricariidae: Pterygoplichthys GILL 1858)

INTRODUCTIONSouth American sailfin catfishes (SACs) have been introduced into natural waterways around the Laguna de Bay basin in the Luzon Island, Philippines (Chavez et al. 2006). Anecdotes claim that SACs were intentionally released into river systems in the Laguna de Bay basin as part of cleanup activities. This event is a probable consequence of its popularity in the local ornamental fish trade where the fish has the moniker “janitor fish” and a reputation of cleaning aquarium tanks. The established population of this fish in the Laguna de Bay is considered a nuisance to fishing families because of the decline in the marketable fish catch in the affected areas. The ecological impact is yet to be seen but similar to other invasion

events it is presumed that displacement of native species and a disruption of the normal ecosystem function will take place.

SACs belong to Family Loricariidae and the genus Pterygoplichthys (known South American sailfin catfishes) have been commonly encountered in the wild and in pet shops (Hoover et al. 2004; Page and Robins 2006). Its introduction has been recorded worldwide in countries such as Puerto Rico (Williams et al. 1994), the United States (994; Sabaj and Englund 1999; Hoover et al. 2004), Taiwan (Liang et al. 2005; Wu et al. 2011), Mexico (Wakida-Kusunoki et al. 2007), Malaysia (Samat et al. 2008), Turkey (Ozdilek, 2007), Bangladesh (Hossain et al. 2008), and Serbia (Simonovic et al. 2010). Current Philippine distribution shows that samples are being collected in brackish waters in the Laguna de Bay

Brion MA et al: Salinity Tolerance of Introduced South American Sailfin Catfishes (Loricariidae: Pterygoplichthys GILL 1858)

Philippine Journal of ScienceVol. 142 No. 1, June 2013

Figure 1. Location map of sailfin catfish in Pasig River. Sampling site is indicated by the black circle. (Abbreviations: MB-Manila Bay; LDB-Laguna de Bay).

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basin suggesting that this range may extend into or via the marine environment. Carandang has collected samples of SACs from the Pasig River (main drainage of the Laguna de Bay to Manila Bay) in the vicinity of km5 from the mouth of the river tributary (Figure 1). Qian et al. (2000) and Carandang reported an average salinity of 5 PSU and 8 g/L salinity in this area, respectively. Collecting SACs from waters with 8 g/L salinity seems atypical of Family Loricariidae, which Myers (1949) claim is strictly a freshwater group of fishes. Some species of freshwater catfishes have been shown to be tolerant to salinity such as in the studies of Buttner et al. 1993, Wurts 1995 and Eckert et al. 2001 for I. punctatus, Fashina-Bombata and Busari 2003 for H. longifilis, Bringolf et al. 2005 for P. olivaris, and while this present report was under review, Capps et al. 2011 for Pterygoplichthys spp.

Salinity is one factor that limits the distribution of many aquatic animals including fishes (Myers 1949; Lee et al. 1981; Fashina-Bombata and Busari 2003; Albert et al. 2004; Bailey et al. 2004; Bringolf et al. 2005; Ovcarenko et al. 2006; Ashton et al. 2007). Tolerance of the SACs to higher salinities could mean further expansion of its range into or via higher salinity environments, thus, increasing its threat as a biological invader. In this study, we tested the toxicity of varied levels of salinity to juvenile sailfin catfishes and determined the median lethal concentration (LC50) of salinity as it implies to potential fish dispersal into marine waters.

MATERIALS AND METHODS

Fish SamplesJuvenile samples were purchased in three batches from pet shops in Cartimar, Pasay City, Philippines. Each batch consisted of 100 fishes with average length of 6.9 cm. Batches were acclimatized for 48 hours in a 70 L holding tank filled with de-chlorinated water, which was circulated using a 600L/hr submersible powerhead. Fishes were fed until satiation thrice daily with commercial fish flakes (TetraFin) and exposed to usual lighting, ambient temperatures, and air circulation in the laboratory. Behavior was likewise noted during feeding times.

Salinity LC50 Toxicity TestingFollowing the OECD Test Guideline 203 (OECD 1992), 96-hour toxicity tests for salinity were carried out using the direct transfer method (Bringolf et al. 2005). A five-treatment, two-replicate design experiment was done using ten 9 L glass aquaria as treatment tanks. The tanks were placed on top of a table exposed to usual light and ambient temperatures in the laboratory, and were maintained independently with an aerator and air stone system. Treatment tanks were arranged in an ABCDEABCDE configuration, and were filled with de-chlorinated water (tank A) or saline water (increasing salinity in tanks B-E) prepared from commercial seawater powder mix (MarinaMix Blue purchased from pet shops



Figure 2. LC50 of salinity on Pterygoplichthys spp. based on the graphical method of intersecting the survival rates and mortality. Dashed line indicates the estimated concentration.

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in Cartimar, Pasay City). A range-finding test was initially done to determine the maximum toxicity limit using these concentrations: 0.0, 5.0, 10.0, 15.0, and 20.0 g/L salinity. Based on the limit from range-finding test, two LC50 determinative tests were then done to determine the median lethal concentration using these salinity concentrations: 0.0, 3.0, 6.0, 9.0, and 12.0 g/L. Salinity was measured using a refractometer.

After acclimation, ten (10) fishes were randomly assigned and placed into a treatment tank. Feeding regimen and light exposure were continued for the duration of the experiment. Behavior of samples was recorded during the first two hours of exposure and subsequently during feeding times. Mortality was the endpoint of the test. Fishes presumed dead were stimulated with a glass rod and subsequently were removed from the experimental tanks when no response was gained. Removed samples were examined by hand and were declared dead when no response was obtained, or were returned to the treatment tank when a response was obtained. Dead fish were tagged prior to storage in a freezer. Samples that survived the experimental tests were later sacrificed by cold torpor. Coloration of a number of samples did not permit species identification but the genus was determined post-mortem by counting the dorsal fin rays after each test (Chavez et al. 2006). For the duration of the experiment, salinities were monitored three times daily using a refractometer. Daily measurements were averaged and considered as the 24-hour salinity readings.

Data Treatment and AnalysisDead fish were recorded immediately and surviving fish were recorded after the tests. The count of surviving and dead fish in each tank was tabulated using MSExcel and data were pooled from each replicate test. LC50

was determined two ways: 1) the graphical method by intersecting the 50% survival rate and mortality; and 2) using Probit ver. 1.5 (USEPA 1992) wherein the lethal concentration was based on non overlapping confidence intervals at 95% (Bringolf et al. 2005). Survival analysis on Pterygoplichthys samples exposed to salinity was performed using the log rank Kaplan-Meier function of SPSS 16.

RESULTSThe count of dead and surviving SAC samples in the experiment is shown in Table 1. The graphical method of determining the LC50 of salinity on Pterygoplichthys samples is depicted in Figure 2. Median lethal concentration of salinity using this method indicates that toxicity starts at around 10.0 g/L. On the other hand, Table 2 shows the estimated LC50 and confidence limits computed using Probit ver.1.5. The computed mean LC50 of salinity is 10.6

Table 1. Data on the salinity toxicity testing using juvenile Pterygoplichthys spp. in a direct transfer exposure experiment. (Abbreviations used: DT=determinative test; RT=range-finding test.)

Salinity (g/L) Test Type

Mortalities Surviving

Hours Hours

24 48 72 96 24 48 72 96

0 Control 0 0 0 1 60 60 60 59

3 DT 0 0 0 1 40 40 40 39

5 RT 0 0 1 0 20 20 19 19

6 DT 0 0 0 1 40 40 40 39

9 DT 0 0 2 4 40 40 38 34

10 RT 0 2 5 1 20 18 13 12

12 DT 0 16 12 2 40 24 12 10

15 RT 1 19 0 0 19 0 0 0

20 RT 20 0 0 0 0 0 0 0



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g/L with confidence limits (at 95%) of 10.2 - 11.2 g/L. Lethal concentration at 50% shows significant difference due to non overlapping salinity values in contrast to the other LC points that exhibit overlaps. The Probit estimate shows that at 10.6 g/L 50% of the samples shows sensitivity to salinity that leads to mortality. Mortality also increases as concentration of salinity increases.

Survival of Pterygoplichthys in varied concentrations of salinity was estimated using the log rank Kaplan-Meier (KM) function in SPSS 16. Table 3 shows the results of the time-to-event model based on this analysis with the test terminated at 96 hours. The KM model in Table 3 shows that Pterygoplichthys spp. is able to tolerate high salinities. Exposed at 12 g/L, samples are estimated to survive up to almost three days (69.6 hours) while at 15 g/L samples can

live up to two days (46.8 hours). At a lower concentration of 9 g/L, juvenile Pterygoplichthys spp. exhibits a strong potential to survive exposure to salinity. Figure 3, illustrates the survival function of Pterygoplichthys spp. as exposed to salinity over a 96-hour period. Notwithstanding the ability to survive at longer periods in high salinity, the graph shows that a good likelihood of the juvenile samples (50% or more) tend to succumb to high salinity gradients. The KM graph shows that the concentrations of salinity at 12 g/L and above decrease the survival of over 50% of the juvenile Pterygoplichthys; it also shows that more that 50% of the samples are projected to tolerate 10 g/L salinity. Log rank analysis of KM model shows significant difference (X2

(df=8;α=0.05); P=0.000) of sample survival times in different salinity concentrations.

Post mortem examination of all 300 samples revealed 9-13 dorsal fin rays indicating that the juveniles belong to genus Pterygoplichthys.

DISCUSSIONThe results indicate that the juvenile South American sailfin catfishes will have a strong chance of survival at salinities of up to 10 g/L. The results also show that at higher salinities and longer exposure times the tolerance of the fish decreases. The derived LC50 in this experiment is higher than the field measurements by Carandang observed for this fish and is comparable to the LC50 results of Bringolf et al. (2005) for four catfish species (range: 10-15.8 0/00 ; average: 13.2 0/00) namely: Pylodictis olivaris (flathead catfish), Ictalurus punctatus (channel catfish), Ameiurus catus (white catfish), and Ameiurus melas (black bullhead). Our salinity tolerance results

Table 2. Acute toxicity of salinity on Pterygoplichthys spp. after 96-hour tests. Concentration and confidence intervals are estimated using Probit ver 1.5.

Lethal Concentration

(%)

Concentration (g/L)

Confidence Interval (95%)

Lower Upper

1 7.4 6.2 8.2

5 8.2 7.2 8.9

10 8.7 7.9 9.3

15 9.1 8.3 9.6

50 10.7 10.2 11.2

85 12.6 11.9 13.8

90 13.0 12.2 14.5

95 13.8 12.8 15.7

99 15.4 14.0 18.3

Table 3. Estimated time of survival of Pterygoplichthys spp. under varied concentrations of salinity with 96 hours as endpoint.

Salinity

Meana Median

Estimate Std. Error95% Confidence Interval

Estimate Std. Error95% Confidence Interval

Lower Bound Upper Bound Lower Bound Upper Bound

0 96.0 0.0 96.0 96.0

3 96.0 0.0 96.0 96.0

5 94.8 1.2 92.4 97.1

6 96.0 0.0 96.0 96.0

9 94.8 0.9 93.0 96.6

10 85.2 3.8 77.7 92.7

12 69.6 3.2 63.3 75.9 72.0 5.8 60.6 83.4

15 46.8 1.2 44.5 49.2 48.0 0.0

20 24.0 0.0 24.0 24.0 24.0

Overall 83.4 1.3 80.8 86.0

note: Estimation is limited to the largest survival time if it is censored.



Figure 3. Survival of juvenile Pterygoplichthys spp. as a function of various salinity concentrations in 96-hour acute toxicity tests. The midline indicates 50% of the sample population.

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for the juveniles are also similar to the limits reported by Capps et al. (2011) for mature Pterygoplichthys pardalis and its hybrids collected in the Grijalva-Usumacinta River delta in Mexico.

Toxicity of higher salinities to South American sailfin catfishes could inhibit its migration to estuarine waters and limit the fish to its current freshwater distribution. Salinity may also limit further dispersal of this fish to other freshwater drainages through the marine coastal route. Bringolf et al. (2005) said that the armor plate cover of catfishes may provide a certain amount of impermeability to salt water. This assumption remains to be verified, however, as well as the other pre-existing physiological mechanisms in the fish such as hormonal response and activation of gill Na+, K+ -ATPase (Mancera and McCormick 1999, 2000), and the role of the

gastrointestinal tract in osmoregulation (Grosell 2011). McCormick (2001), Evans (2008) and Grosell (2011) offer good reviews on fish osmoregulation.

Human activity has facilitated the movement of species across traditional barriers and outside of historical distributions. The association between salinity and distribution of fish species are usually seen as part of taxonomic reports and rarely is this association examined unless for warranted reasons. Aquaculture is one of the major routes of fish invasions (Casal 2006) and it is one of such warranted reasons where the association of salinity and distribution is studied such those by: Fashina-Bombata and Busari (2003) on African catfish; Luz et al. (2008) on goldfish; Lee et al. (1981) on sand smelt; and Hena et al. (2005) for tilapia. Another reason is range expansion and environmental impact of invasive species

Time (h)

Time (h)

Survival FunctionsSu

rviv

al (%

)



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as reported by: Eckert et al. (2001) and Bringolf et al. (2005) for ictalurid catfishes; Schofield et al. (2006) for goldfish; Ashton et al. (2007) for caprellid shrimps, and Capps et al. (2011) for Pterygoplichthys.

Fish limits itself to suitable salinities because of the stress exerted on osmoregulation by the surrounding water medium. This therefore becomes an important aspect of biogeographic distributions of species as Myers (1949) has pointed out previously. But as species are redistributed to new landscapes and historical biogeographic distributions are disturbed, new physiological responses to stress are observed. When species, such as freshwater fish, are introduced into new environments, existing environmental conditions impose new levels of stress, which brings about physiological responses never before accounted in literature particularly in taxonomic descriptions. In our study of the South American sailfin catfish invasion, we relied on existing literature on the fish, particularly taxonomic descriptions, to gain insights that are useful for the control and management of invasions, and the mitigation of invasion effects. We found in this case that the reliability of taxonomic characterizations of species become limited because of the generalizations that are made on physiological responses of species, and the inadequacy of species characterizations based on historical or traditional distributions, which do not take into account the existence of ecotypes. Family Loricariidae as a freshwater fish family has been described in Mayers (1949) and Nelson (1994) but the tolerance limits to changes in salinity has not been documented for members of this fish family until Capps et al. (2011) and this present report. With a confounding lack of empirical evidence such as in this case at hand, it might be safe to assume that freshwater fish exhibits certain tolerances to changes in salinity but this is an assumption substantiated only by studies such as ours and Capps et al. (2011). In our observation, the physiological response towards salinity exhibited by Pterygoplichthys is notable because this is atypical and diverges from the usual features attributed to it under its taxonomic family in existing literature, which is based on its original range of distribution and does not account the existence of ecotypes.

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