Hostname: page-component-74656f9884-2dmjx Total loading time: 0 Render date: 2026-11-09T02:18:36.431Z Has data issue: false hasContentIssue false
  • English
  • Français

Length–weight relationships in syngnathid species from Tunisian waters (central Mediterranean)

Published online by Cambridge University Press:  19 May 2011

M.M. Ben Amor ,
M. Ben Salem ,
C. Reynaud  and
C. Capapé
M.M. Ben Amor*
Affiliation:
National Institute of Sea Sciences and Technologies (INSTM), Fishing Port 2060, La Goulette, Tunisia Unité de Recherches Zoologie et Ecologie des Milieux aquatiques, Faculté des Sciences of Tunis, University Tunis El Manar, 2092 Tunis, Tunisia
M. Ben Salem
Affiliation:
Unité de Recherches Zoologie et Ecologie des Milieux aquatiques, Faculté des Sciences of Tunis, University Tunis El Manar, 2092 Tunis, Tunisia
C. Reynaud
Affiliation:
Laboratoire Interdisciplinaire de Recherche sur la Didactique, l'Éducation et la Formation, E.A. 3749, case 77, Université Montpellier II, Sciences et Techniques du Languedoc, 34 095 Montpellier cedex 5, France
C. Capapé
Affiliation:
Laboratoire Interdisciplinaire de Recherche sur la Didactique, l'Éducation et la Formation, E.A. 3749, case 77, Université Montpellier II, Sciences et Techniques du Languedoc, 34 095 Montpellier cedex 5, France
*
Correspondence should be addressed to: M.M. Ben Amor, National Institute of Sea Sciences and Technologies (INSTM), Fishing Port 2060, La Goulette, Tunisia email: benamor7@yahoo.fr

Abstract

Length–weight relationships of four pipefish and two seahorse species from Tunisian waters are presented in this paper: the straight-nosed pipefish Nerophis ophidion, the black-striped piperfish Syngnathus abaster, the greater pipefish S. acus, the deep-snouted piperfish S. typhle, the short snouted seahorse Hippocampus hippocampus and the long-snouted seahorse Hippocampus. ramulosus. Overall, 2424 specimens of these six syngnathid species were weighed and measured. The sample size ranged from 14 for N. ophidion to 1773 for H. ramulosus. The values of the slope b in the length–weight relationships (W = aLb) varied between 1.836 (S. typhle) and 5.476 (N. ophidion). Linear regressions of length–weight relationships were significant for all species. We have calculated a positive allometry in weight versus length for N. ophidion, an isometry for H. hippocampus and H. ramulosus and a negative allometry for S. abaster, S. acus and S. typhle.

Keywords

OsteichthyesSyngnathidaelength–weight relationshipTunisian waterscentral Mediterranean

Information

Type
Research Article
Information
Marine Biodiversity Records , Volume 4 , December 2011 , e44
Copyright
Copyright © Marine Biological Association of the United Kingdom 2011

INTRODUCTION

Of the 17 syngnathid species known from the Mediterranean (Dawson, Reference Dawson, Whitehead, Bauchot, Hureau, Nielsen and Tortonese1986; Lourie et al., Reference Lourie, Vincent and Hall1999), seven have been recorded in Tunisian waters to date (Bradaï et al., Reference Bradaï, Quignard, Bouaïn, Jarboui, Ouannes-Ghorbel, Ben Abdallah, Zaouali and Ben Salem2004; Ben Amor et al., Reference Ben Amor, Ben Salem, Ben Souissi and Capapé2006, Reference Ben Amor, Ben Souissi, Ben Salem and Capapé2007a, Reference Ben Amor, Ben Salem, Ben Souissi and Capapéb, Reference Ben Amor, Ben Salem, Ben Souissi and Capapé2008a, Reference Ben Amor, Ben Salem, Ben Souissi and Capapéb): two seahorses, the short snouted seahorse Hippocampus hippocampus (Linnaeus, 1758) and the long-snouted seahorse Hippocampus ramulosus Leach, 1814; five pipefish, the straight-nosed pipefish Nerophis ophidion (Linnaeus, 1758), the black-striped piperfish Syngnathus abaster Risso, 1826, the greater pipefish S. acus Linnaeus, 1758, the deep- snouted pipefish S. typhle Linnaeus, 1758 and Nilsson's pipefish Syngnathus rostellatus Nilsson, 1855, which was first recorded in the Gulf of Tunis by Ben Amor et al. (Reference Ben Amor, Ben Salem, Ben Souissi and Capapé2008b).

The aim of this paper is to study length–weight relationships of four pipefish and two seahorses. Such relationships are important because they allow the estimation of condition in teleost species, the conversion of length to biomass, and to carry out comparisons of the condition of individuals of the same species caught in other marine areas. Additionally, they are useful to determine whether or not somatic growth is isometric, positively allometric, or negatively allometric.

MATERIALS AND METHODS

Between January 2000 and December 2007, sampling was carried out at fish landing sites located along the Tunisian coast and, in brackish lagoons such as Bizerte Lagoon, Tunis Southern Lagoon and Bahiret El Biban (Figure 1). Two seahorse species, Hippocampus hippocampus and H. ramulosus and four pipefish species, Syngnathus abaster, S. acus, S. typhle and Nerophis ophidion were collected monthly using trammel nets (mesh size 20 mm) and experimental mobile fishing gear (dredging) on seagrass beds of Posidonia oceanica and some algae species such as Caulerpa prolifera, C. racemosa, Cystoseira stricta, C. crinita and Rythiphlaea tinctoria.

Fig. 1.

(A) Map of the Mediterranean Sea showing map of Tunisia; (B) map of Tunisia showing the capture sites of syngnathid species in Tunisian waters: 1, Bizerte Lagoon (BL); 2, Tunis Northern Lagoon (TNL) and Tunis Southern Lagoon (TSL) separated by navigation channel (NC); 3, Bahiret El Biban (BB).

A total of 2424 specimens of these six different species of syngnathidae were collected and identified following field guides such as Dawson (Reference Dawson1982, Reference Dawson, Whitehead, Bauchot, Hureau, Nielsen and Tortonese1986) and Lourie et al. (Reference Lourie, Vincent and Hall1999). Sample sizes ranged from 14 Nerophis ophidion, to 1773 for Hippocampus ramulosus. Soon after captures, fresh specimens were studied in the laboratory. After identification, they were sorted by sex, measured to the nearest 1 mm (total length, TL) and weighed to the nearest 0.1 g (weight, W). Additionally, TL of seahorses is expressed as the sum of head length, trunk length and tail length, using a curved measurement of trunk length from the midcleithral ring to the last trunk ring (Lourie et al., Reference Lourie, Vincent and Hall1999).

The length–weight relationship for total body weight was fitted W = aL b (Ricker, Reference Ricker1973), where W is weight (expressed in grams), L is length (expressed in mm), a is the intercept and b is the slope (Beverton & Holt, Reference Beverton and Holt1996). The degree of association between the variables was computed by the coefficient of determination, r 2. The parameters a and b were estimated by linear regression using the log-transformed equation Log(W) = Log(a) + bLog(L). The significance of the regression was assessed by analysis of variance, and the Student's t-test was applied to verify whether the slope of the regression (constant ‘b’) differed significantly from 3.0, indicating the type of growth: isometric (b = 3.0), positive allometric (b > 3.0) or negative allometric (b < 3.0) (Spiegel, Reference Spiegel1991). In all cases, a significance level of 0.05 was adopted.

RESULTS AND DISCUSSION

Length–weight relationships of four pipefish and two seahorse species collected in Tunisian waters are given in Table 1. Relationships (linear regressions) were significant for all species, with r 2 values greater than 0.84. Estimated values of b were close to 3.0 (P > 0.05) for both Hippocampus hippocampus and H. ramulosus, indicating an isometric growth. The values of the exponent b were significantly (P < 0.05) higher than 3.0 for Nerophis ophidion exhibiting positive and allometric growth. The slopes for Syngnathus abaster, S. acus and S. typhle were also significantly different (P < 0.05), but lower than 3.0, reflecting a negative allometric growth. Differences observed among these species could, in part, be due to sampling, since only 14 N. ophidion were collected, compared to the much greater numbers of species of seahorses which are the most abundant syngnathid species in Tunisian waters (Ben Amor et al., Reference Ben Amor, Ben Salem, Ben Souissi and Capapé2008b). Hippocampus hippocampus and H. ramulosus both presented an isometric allometry. Additionally, no significant differences were found between them even though specimens of the latter species were collected in four different brackish areas, while the former was collected in a single one. By contrast, length–weight relationships of the three syngnathid species showed significant negative allometry, with these latter probably being more sensitive to unfavourable environmental conditions in restricted brackish areas.

Table 1.

Descriptive statistics and estimated parameters of length–weight relationship for six species collected from Tunisian waters.

N, sample size; SE, standard error; Range, minimum and maximum; a and b, parameters of the length–weight relationship; r 2, coefficient of determination; Mean TL, mean length in mm; Mean W, mean weight in g. *, P<0.05; ns, P > 0.05.

Studies conducted in other Mediterranean areas reported values ranging from 2.88 to 3.73 for Syngnathus acus, and from 2.94 to 3.22 for S. typhle, that are higher than those recorded for specimens from Tunisian waters, which were 2.64 for the former and 1.84 for the latter. These latitudinal differences could be due to sampling, but could also be associated to unfavourable environmental conditions in Tunisian waters. However, the higher value of b for N. ophidion than those from other areas suggests that the species probably finds favourable environmental conditions in Tunisian waters. Nevertheless, sampling effects cannot be neglected, but further observations are needed to confirm such a hypothesis. Our results showed that isometric allometries were recorded for both H. hippocampus and H. ramulosus. A similar pattern was observed by Gurkan & Taskavak (Reference Gurkan and Taskavak2007) for specimens from I̊zmir Bay, in Turkish waters. By contrast, there is a significant difference between the length–weight relationships for all pipefish and H. ramulosus of Tunisian waters and other sites. The length–weight relationship in fish can be affected by a number of factors including season, habitat, gonad maturity, sex, diet and stomach fullness, health and preservation techniques and differences in the length range of the specimen caught (Tesh, Reference Tesh and Ricke1971; Wootton, Reference Wootton1998). This difference in length–weight relationships between this and other studies could potentially be attributed to the combination of one or more of the factors cited above (Table 2).

Table 2.

Comparison between available studies on length–weight relationship for Syngnathus acus, S. typhle, Nerophis ophidion, Hippocampus hippocampus and H. ramulosus in other Mediterranean areas.

N, sample size; a and b, parameters of the length–weight relationship; r 2, coefficient of determination.

References

REFERENCES

Beverton, R.J.H. and Holt, S.J. (1996) On the dynamics of exploited fish populations. Fishery Investigation, London, Series 2, 1–533.Google Scholar
Ben Amor, M.M., Ben Salem, M., Ben Souissi, J. and Capapé, C. (2006) Observation on the black-striped pipefish, Syngnathus abaster Risso, 1810 (Osteichthyes: Syngnathidae) from the Tunisian waters (central Mediterranean). Annales, Series Historia Naturalis 16, 193–198.Google Scholar
Ben Amor, M.M., Ben Souissi, J., Ben Salem, M. and Capapé, C. (2007a) Confirmed occurrence of the straight-nosed pipefish, Nerophis ophidion (Syngnathidae) in southern Tunisia (central Mediterranean). Cybium 31, 483–484.Google Scholar
Ben Amor, M.M., Ben Salem, M., Ben Souissi, J. and Capapé, C. (2007b) On the occurrence of the deep-snouted pipefish Syngnathus typhle Linnaeus, 1758 (Osteichthyes: Syngnathidae) in the Tunisian waters (Central Mediterranean). Acta Adriatica 48, 15–23.Google Scholar
Ben Amor, M.M., Ben Salem, M., Ben Souissi, J. and Capapé, C. (2008a) The syngnathid species (Osteichthyes) from Tunisian waters (Central Mediterranean): a survey. Annales, Series Historia Naturalis 18, 1–10.Google Scholar
Ben Amor, M.M., Ben Salem, M., Ben Souissi, J. and Capapé, C. (2008b) Occurrence of the Nilsson's pipefish Syngnathus rostellatus (Osteichthyes, Syngnathidae) in the Gulf of Tunis (Central Mediterranean). Vie et Milieu 58, 1–4.Google Scholar
Bradaï, M.N., Quignard, J.-P., Bouaïn, A., Jarboui, O., Ouannes-Ghorbel, A., Ben Abdallah, L., Zaouali, J. and Ben Salem, S. (2004) Ichtyofaune autochtone et exotique des côtes tunisiennes: recensement et biogéographie. Cybium 28, 315–328.Google Scholar
Coull, K.A., Jerym, A.S., Newton, A.W., Henderson, G.I., and Hall, W.B. (1989) Length/weight relationships for 88 species of fish encountered in the North Atlantic. Scottish Fisheries Research Report 43, 80.Google Scholar
Dawson, C.E. (1982) Fishes of western North Atlantic. Part 8. Order Gasterosteiformes, Suborder Syngnathoidei, Syngnathidae. Sears Foundation for Marine Research, Memoir 1, 1–197.Google Scholar
Dawson, C.E. (1986) Syngnathidae. In Whitehead, P.J.P., Bauchot, M.-L., Hureau, J.-C., Nielsen, J. and Tortonese, E. (eds) Fishes of the north-western Atlantic and the Mediterranean. Volume 1. Paris: Unesco, pp. 628–639.Google Scholar
Gurkan, Ş. (2004) Investigations on the ecomorphologic characteristics of the pipefish (Familia: Syngathidae) distributing in the Çomati Lagoon ( I̊zmir Bay). PhD thesis. Egee University, Department of Hydrobiology, I̊zmir, 215 pp.Google Scholar
Gurkan, S. and Taskavak, E. (2007) Length–weight relationships for syngnathid fishes of Aegean Sea, Turkey. Belgian Journal of Zoology 137, 219–222.Google Scholar
Koutrakis, E.T. and Tsikliras, A.C. (2003) Length–weight relationships of fishes from three northern Aegean estuarine systems (Greece). Journal of Applied Ichthyology 19, 258–260.CrossRefGoogle Scholar
Lourie, S.A., Vincent, A.C.J. and Hall, H.J. (1999) Seahorses: an identification guide to the world's species and their conservation. London: Project Seahorse, 214 pp.Google Scholar
Ozaydin, O. and Taşkavak, E. (2006) Length–weight relationships for 47 fish species from I̊zmir Bay (Aegean Sea, Turkey). Acta Adriatica 47, 211–216.Google Scholar
Ricker, W.E. (1973) Linear regression in fishery research. Journal of the Fisheries Research Board of Canada 30, 409–434.CrossRefGoogle Scholar
Spiegel, M.R. (1991) Théorie et applications de la statistique. Paris: McGraw-Hill.Google Scholar
Tesh, F.W. (1971) Age and growth. In Ricke, W.E. (ed.) Methods for assessment of fish production in fresh waters. Oxford: Blackwell Scientific Publications, pp. 98–130.Google Scholar
Valle, C., Bayle, J.T. and Ramos, A.A. (2003) Weight-length relationships for selected fish species of the western Mediterranean Sea. Journal of Applied Ichthyology, 19, 261–262.CrossRefGoogle Scholar
Wootton, R.J. (1998) Ecology of teleost fishes. Dordrecht, The Netherlands: Kluwer Academic Publishers.Google Scholar
Worthmann, H. (1975) Das Makrobenthos und Fischbesiedlung in verschiedenen Flachwassergebieten der Kieler Bucht (Westl Ostsee). Kiel University, 141 pp. Thesis.Google Scholar
Figure 0

Fig. 1. (A) Map of the Mediterranean Sea showing map of Tunisia; (B) map of Tunisia showing the capture sites of syngnathid species in Tunisian waters: 1, Bizerte Lagoon (BL); 2, Tunis Northern Lagoon (TNL) and Tunis Southern Lagoon (TSL) separated by navigation channel (NC); 3, Bahiret El Biban (BB).

Figure 1

Table 1. Descriptive statistics and estimated parameters of length–weight relationship for six species collected from Tunisian waters.

Figure 2

Table 2. Comparison between available studies on length–weight relationship for Syngnathus acus, S. typhle, Nerophis ophidion, Hippocampus hippocampus and H. ramulosus in other Mediterranean areas.