Short Communication Ecological observations on the ...

S. Afr. J. Wild\.

108

Res. 1997,27(3)

& Mhaisen (1991) and a single paper on morphology (Kruger. Avenant-Oldewage & Wepener in press). M.

Short Communication Ecological observations on the fish ectoparasite Mugilicola smithae (Crustacea: Copepoda)

smithae is the only representative in Africa and was originally found on freshwater eels. Anguilla mossambicus Peters, 1852. in the Keiskarnrna and Umtata Rivers (Jones & Hine 1978), but specimens were recently found in the Nhlabane Estuary on. These were identified to be M. smithae (Kruger et al. in press). Although

few data are available

owing

to the low

W. Kruger and A. Avenant-Oldewage*

number of hosts caught. the lack of any ecological

Department of Zoology, Rand Afrikaans 524, Auckland Park, 2006 South Africa

this genus justifies publication. Five surveys were carried out during 1995 and 1996 at Nhlabane Estuary (28°25'E; 32° I D'S), approximately 22 krn north-east of Richards Bay in Kwazulu-Natal (Figure I). The estuary is ± 3 krn long and reaches a depth of 3.8 m at its deepest point. Mining of a vari-

University, P.O. Box

.D.P. Cyrus Department of Zoology, University of Zululand, Private Bag X10017 Kwadlangezwa, 3886 South Africa Received 2(}August /996: accepted 5 August /997 During the period of January 1995 to February 1996, five surveys were carried out in Nhlabane Estuary in KwazuluNatal to determine prevalence, abundance and mean intensity of the fish ectoparasite Mugilicola smithae. The forklength and sex of the host fishes were also recorded, as well as physical water quality values. No preference to either male or female host fishes was found. Prevalence, mean intensity and abundance showed no correlation to the physical factors. Most infested hosts were between 200 and 300 mm. Lengths of the parasites collected showed no correlation to season, and most of the parasites were between 5 mm and 7 mm in length. It is therefore suggested that this ectoparasite produces eggs throughout the year, and that parasite intensity is not affected by the physical water quality. Keywords: Crustacea, ectoparasite, smithae, mullet

* To

whom correspondence

estuary, Mugilicola

should be addressed

Four species of the genus Mugilicola have been described of which only M. smithae (Jones & Hine 1978) has been found in South Africa. To date four publications of taxonomic nature have been published on this genus i.e. Tripathi (1960). Jones & Hine (1978), Boxshall (1986) and Piasecki. Khamees

ety of elements including

zirkoniurn

(Zr), titanium

iron (Fe) takes place. Freshwater from enters the estuary via subterranean flow. The Nhlabane years preceding

breached in

August 1995. The re-opening of this system had a profound influence on juvenile fish recruitement into the system. The salinity of the estuary increased and changes occurred in the vegetation composition. The latter had an effect on factors such as turbidity. water temperature, ecological niche composition as well as the effort to collect hosts (mullets). Surveys were carried out in January, April, tember

1995, and February

June and Sep-

1996, to represent seasonal sur-

veys. Dissolved oxygen values were obtained with the aid of a WTW Microprocessor Oximeter Model OXI96. Turbidity was measured with a Hach Turbidity meter Model 2100A. and pH with a Mettler Toledo Microcep microprocessor. Fishes were collected with 50 stretched mesh monofilament gill Nets were left ill the water for before they were hauled in. Fish

rnrn. 75 rnrn and 100 rnrn nets. as well as seine nets. a minimum period of 5 h were killed by a single cut

through the spinal cord. after which the gills were dissected out and examined with the aid ofa Wild M5 dissection micro-

Lac Nhlabanc

a

I ~

the sampling

ponds

Estuary was closed off from the sea for five

~----

I Map indicating

(Ti), and

the mining

the survey. and was artificially

Zululand

Figure

data on

site for Mugilicola smithae. (a) All surveys

were conducted

in the Nhlabane

Estuary.

S. Afr. 1. WildL Res. 1997.27(3)

109

35

~

e

:E

Ltza

alata

Llza

mscrotems

30

m MyxIS

25

[J Va/smugi' sehell

"g20

0;

~

o

no'

•

15

Infested

ceoensse

hosts

(n=number of parasites)

+ 10

o4-------~--LL~_. 0-100mm

lQl-200mm

201-300mm

301-400mm

+401mm

Length of hosts

Figure 3 Intensity of .H. stnithac parasites recorded from hosts of different lengths.

Figure 2 Mugilicola smithae specimen attatched to gill.

II

ith nee

(n) burrowed in gill arch (ga). and abdomen (ab) and egg-sacks (es visible between gill filaments (gf).

scope for the presence of M. smithae. The length. weight and sex of each host. as well as the length 01" the parasites were recorded. Attachment sites on the host's body were also noted. M. smithae females are sessile and permanentely attached to the host fish where they become sexually mature and release their eggs. These ectoparasites attach only to the gills and more specifically to the gillarches (Figure 2). In some cases up to 50% of the total body is embedded in the gillarches with only the abdomen and eggsacks visible between the gill filaments. l.iza a/ala (53 individuals), Liza macrolepis (n = 47), Myxis capensis (n = 7), Valamugil seheli (n = 13), Oreochromis mossambicus (n = 14), Clarias gariepinus (n = 8), and Sphyraena barracuda (n = 3) were collected. Only L. alata. L. macro/epis. M. capensis and V. sehe/i were infested with M. smithae all of whom are representative of the family Mugilidae. Parasitological data is presented as suggested by Margolis. Esch. Holmes. Kuris & Schad (1982) and term inology is defined as follows. Prevalence: Number of individuals of a host species infested with a particular parasite species divided by the number of hosts examined and can be expressed as a percentage. Mean intensity: Total number of individuals of a particular parasite species in a sample of a host species divided by the number of infested individuals of the host species in the sample. (Mean number of particular parasite species per infested host). Abundance: Total number of individuals of a particular parasite species in a sample of hosts divided bv the total number of individuals of the host species (infested + uninfested) in the sample. (Mean number of particular parasite species per host examined). The fork length of infested hosts varied between

100 mm

between 200 mm and 300 mm. None of the fish examined were shorter than 100 mm. The highest intensity of parasites was recorded from fish with lengths between 201-300 mm (Figure 3). A x2-test for males and females was conducted, indicating no preference for male or female hosts. A higher number of female Liza a/ata and L. macrolepis were collected. Parasites collected from M. capensis and /. scheli showed no preference towards male or female fishes. a M. capensis were infested (only three female fish were caught). The total lengths of parasites collected ranged between 4 mm and 9 mrn, with a mean value of 6.2 mm and a standard deviation of 1.26 mm. During each of the surveys lengths of 6 mm to 7 mm were most frequently recorded (Figure 5). Dissolved oxygen and pH values were fairly constant throughout the study (Figure 4a). The temperature showed the expected seasonal fluctuation (Figure 4a). The salinity showed a sudden increase after July owing to the breaching of the estuary. The lowest prevalence was recorded in June when few fishes were collected and the highest prevalence was recorded in April. All four host fish species were not collected during each survey therefore comparing prevalence is hindered (Figure 4d). The highest mean intensity for M. capensis was recorded during April with a value of eight. This value is very high in comparison with the values obtained from the other three species but it must be stated that only one of the four M. capensis collected was infested. Valamugil seheli showed the second highest mean intensity with a value of five. but again it must be stated that there were five parasites on a single fish. Liza a/uta and L. macrolepis showed little variation in mean intensity (Figure 4c). There is a number of possible reasons for the low fish catches recorded during the study. Temperature could have influenced the collection of fish especially during the July survey when the fish were less motile. and also more concentrated in dense submerged aquatic macrophytes unreachable by boat. Furthermore. extensive gill-netting by the rural community, where fish constitutes a major food source, may have attributed 'to the low catches. Fish are preyed upon by crocodiles and predatory fish such as S. barracuda (barracuda). Mullet numbers decreased after the breaching of the estuary as the mullets migrated towards the sea to spawn during win-

and 700 mm. Eighty percent of all infested fish had lengths

ter and spring as is characteristic

between 200 rnrn and 400 mm and 70% thereof

Heemstra 1986).

lengths

of their nature (Smith &

S. Afr. J. Wild!. Res. 1997,27(3)

110

30

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CO

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