Spawning frequency, fecundity, egg weight and spawning type of silver pomfret, Pampus argenteus (Euphrasen) (Stromateidae), in Kuwait waters By S. M. Almatar, K. P. Lone, T. S. Abu-Rezq and A. A. Yousef Mariculture and Fisheries Department, Kuwait Institute for Scientific Research, Salmiya, Kuwait Summary Silver pomfret, Pampus argenteus, were collected by fishing with drift gillnets on one spawning ground in Kuwait waters during 1998–2000. Fish size frequency, sex ratio, maturation cycle, spawning frequency, fecundity and egg weight were assessed. The length–weight relationship differed between sexes whereby females were significantly bigger than males. Spawn- ing started in mid-May and continued until early October. During this time the water temperature ranged from 26.0 to 32.8°C, salinity was @ 39.0& and water depth ranged between 5 and 12 m. Large females spawned earlier than young spawners and the overall percentage of males during the spawning period was 70.3%. Spawning occurred after 13.00 h, with peak spawning between 15.00 and 18.00 hours during outgoing tide. Mean daily spawning frequency amounted to 63.2%. Spawning activity was found to be associated with the lunar cycle and spawnings were concentrated during the first and third quarters of the moon period, indicating a semilunar reproduction cycle. It was concluded that a female would spawn at least six times during the season. No change was observed in relative fecundity during the peak spawning season (June–August). Average relative batch fecundity was 176.3 eggs g )1 somatic weight (SW), corresponding to a relative total fecundity of 1058 eggs g )1 SW, which is 1.5 times higher than estimates obtained from counting the standing stock of oocytes. Bigger fish produced heavier eggs and the egg weight decreased as the spawning season progressed. Based on gonadal cycles, oocyte size frequency distribution and total fecundity, we concluded that silver pomfret is a multiple batch spawner with indeterminate fecundity. Introduction Silver pomfret, Pampus argenteus (Euphrasen 1788), is a valuable fish species for human consumption with a market demand worldwide. It is common in coastal waters with an extensive geographical distribution ranging from the Sea of Japan, around the Indian subcontinent to the Arabian Gulf (Haedrich, 1967). Few but contradicting reports related to the reproductive biology of silver pomfret are available (Gopalan, 1969; Pati, 1981; Abu-Hakima, 1984; Kim and Han, 1989; Dadzie et al., 1998, 2000a; Almatar et al., 2000). Studies on fecundity of silver pomfret are limited to counting the standing stock of advanced yolked oocytes (Pati, 1981; Abu-Hakima, 1984; Dadzie et al., 2000a), assuming determinate fecundity (Hunter et al., 1992). Recent studies indicate that many temperate and tropical fish have an indeterminate fecundity (Hunter and Goldberg, 1980; DeMartini and Fountain, 1981; Conover, 1985; Hunter and Macewicz, 1985; Greer Walker et al., 1994; Lowerre-Barbieri et al., 1996). No studies on silver pomfret to date have considered the spawning frequency or re-evaluated the assumption of determinate fecundity. The purpose of this paper is to describe the spawning pattern of silver pomfret in Kuwait waters and to determine reproductive parameters such as fecundity type (i.e. determinate or indeterminate) and egg weight. Materials and methods Collection of samples and measurements Collection of silver pomfret with drift gillnets was carried out on one spawning ground covering about 40 km 2 in Kuwait waters located between latitude 29°22¢N and 29°24¢N; and longitude 48°00¢E and 48°06¢E (Fig. 1). Gillnets were deployed 2–5 km offshore in 5–12 m depth for about 30 min per haul. One net unit was made of monofilament of 24 m length and 11 m height with a mesh size of 14 cm. One set of nets contained 40 units. Two fibreglass speedboats were utilized in fishing and several hauls were made during each daily trip using one set of nets per boat. Fishing was conducted from May 1998 to October 1999 and from May to September 2000 as part of a programme to collect running-ripe fish for artificial fertilization. Number of fishing days per year was 50, 55 and 42 in 1998, 1999 and 2000, respectively. Daily fishing time ranged between 06.00 and 20.00 hours. Bottom water temperatures and salinities were measured with a portable Yellow Spring Inc. (Ohio, USA) model 550 temperature and salinity meter. Fork length (FL) and standard length (SL) of all captured fish were measured to the nearest mm. Total length in P. argenteus was found to be highly variable because of natural trimming of tail fins and was therefore not recorded. Total weight (TW), somatic weight (SW) without gonads and intestines and gonad weight (GW) were measured in the laboratory for all females and for random samples of males to the nearest 0.1 g. Gonads were excised, weighed and develop- mental stage recorded and then preserved in 5% buffered formalin diluted with full-strength seawater (39&). Males were classified as spawning if milt was excreted by applying gentle pressure on the abdomen or non-spawning if no milt was observed. Preserved ovaries were used to estimate fecundity and oocyte size frequency distribution, and to provide samples for histological investigations. Preliminarily macroscopic descriptions of the ovary were recorded according to the classification of Gopalan (1969) and later verified histologi- cally. Detailed macroscopic and microscopic descriptions of ovarian developmental stages are shown in Table 1. J. Appl. Ichthyol. 20 (2004), 176–188 Ó 2004 Blackwell Verlag, Berlin ISSN 0175–8659 Received: August 1, 2003 Accepted: September 17, 2003 U.S. Copyright Clearance Centre Code Statement: 0175–8659/2004/2003–0176$15.00/0 www.blackwell-synergy.com