The weight (W) of fishes (and other organisms) is exponentially related to their length (L) according to the equation W = aL b , where a is the intercept and b is the slope of the log-transformed relation (Le Cren 1951, Froese 2006. Based on the slope (b) of the relation between weight and length, one can check whether the growth of a fish species is isometric (b = 3, all fish dimensions increase at the same rate), hypoallometric (b < 3, a fish increases less in weight than predicted by its increase in length, i.e., it becomes more elongated as it grows; also termed negative allometric) or hyperallometric (b > 3, a fish increases more in weight than predicted by its increase in length, i.e., it becomes less elongated or more roundish as it grows; also termed positive allometric). Weight-length relations (WLRs) can be used for converting lengths into biomass, determining fish condition, comparing fish growth among areas, and as a complement to species-specific reproduction and feeding studies (Petrakis and Stergiou 1995, Koutrakis and Tsikliras 2003, Froese 2006. Thus, they are an important component of fisheries biology and when properly calculated they can be very useful to fisheries management.Over the last decade, the number of published articles dealing with WLRs of fishes is increasing in fast rate (Fig. 1). The majority of articles have been published in specialized fish journals, with 367 out of the 697 articles appear- In this editorial note, we set some criteria and recommendations on important issues (i.e., number of species, sample size, length range and preservation, reporting and Abstract. Weight-length relations of fishes are useful for estimation of biomass from length observations, e.g., in fisheries or conservation research. Here we provide some guidance to authors of such papers, in order to facilitate the publication and review process. EDITORIAL NOTE ON WEIGHT-LENGTH RELATIONS OF FISHES

In 18 marine fish species from the eastern Mediterranean, vertical mouth opening increased linearly with total length (LT) for 10 species and log‐linearly for eight species. Horizontal mouth opening was linearly related to LT for 12 species and log‐linearly for six species, whereas mouth area was a log‐linear function of LT for all fish species examined. Mouth shape varied greatly covering the whole spectrum from a full circle to an extended oval. In addition, the trophic level of the 18 species could be expressed as an asymptotic function of mouth area. The results are discussed within the context of the trophic ecology of the species examined in the study area.

We collected all available information (i.e. international and local journals, conference proceedings, theses, technical reports) on the spawning season (n = 511 stocks, 168 species), gonadosomatic index (n = 237 stocks, 81 species) and sex ratio (n = 97 stocks, 68 species) of Mediterranean marine fish. The 511 stocks represented 20 orders (most were Perciformes, 283 stocks) and 65 families (most were Sparidae: 17 species and 63 stocks). Overall, 346 stocks (128 species) spawned between April and August, 139 stocks (60 species) between September and March, while the remaining 26 stocks (13 species) were all-year-round spawners. In addition, 174 stocks (34.1%) were characterised by an extended ([4 months) spawning season, but, for most stocks (332 stocks, 64.4%), spawning duration ranged from 2 to 4 months inclusive. Regardless of the onset and the duration of spawning, the spawning period of 284 and 287 stocks included June and July, respectively, indicating that most Mediterranean species are summer spawners. Female gonadosomatic index ranged between 0.06 and 37 (mean ± SE = 8.55 ± 0.647, n = 95) and was significantly higher (t-test: t = 5.58, P \ 0.001) than the corresponding male one, which ranged between 0.06 and 30 (mean ± SE = 4.21 ± 0.431, n = 95). Congeneric species that occupied the same area and share the same requirements exhibited successive and non-overlapping spawning (e.g. Sparidae in the Adriatic Sea, Mugilidae in the Ionian Sea and Tunisian waters). The knowledge of the spawning period coupled with information on spawning and nursery grounds and detailed knowledge of mating systems, social interactions, maturity and fecundity may be very useful for fisheries management.

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The feeding habits of Zeusfaber Linnaeus, 1758 were studied by examining digestive tracts in I2 size classes of individuals. It is a stenophagus species which begins life feeding almost exclusively on zooplankton until it is about 80 mm long, then switches gradually from zooplankton to small demersal fish, and finally when > 140 mm switches to feeding exclusively on benthic and demersal fish. Mysids were the most important food component in Z.faber < 141 mm and Cepola macrophrhalmu (Linnaeus, 1758) in Z . fiber 140 mm. The switch to fish prey was followed by a greater body weight per unit length. Z . faber > 140mm selected primarily for smalland intermediate-sized C. macrophthalma (and to a lesser extent for Cullionymus maculatus Rafinesque-Schmaltz, 1810, Guidropsarus sp. and Trzgla Iyra Linnaeus, 1758). Our results suggested that the ratio of vertical to horizontal dimension of prey, the motion and coloration of prey as well as the visual capabilities and perceptual potentialities of 2. fuber may all in a synergetic fashion account for prey type and size selection and the positive relations found between the size of 2.faber and the size and variance ofits ingested prey. Possible co-evolutionary relationships between Z..faber and C. macrophfhalma are also discussed.

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