Length-Weight Relationship of Two Creek Associated Mangrove Fishes, Gorai Creek, Mumbai, India

The Gorai creek, commercially used for the transportation, lies between the Borivali and Gorai village, Sub-urban Mumbai, Maharashtra (19.2253°N, 72.8215°E and 19.2282°N, 72.8059°E). For the present study, five different sampling sites were fixed such as, interior of the creek towards freshwater inlet (site-1: 19.2311, 72.8186), mid-way near to mangrove areas (site-2: 19.2214, 72.8071), ear to Essel World- Global Vipassana Pagoda (site-3: 19.2124, 72.8048), in near to off mangrove areas (site-4: 19.2063, 72.7992) and near to Gorai beach (site-5: 9.1997, 72.7952) towards the mouth of creek. The fishing trials were conducted along the creek area in monthly intervals from August, 2019 to July, 2020. The dol nets, measuring about 15 m in total length equipped with float line and hauling line made up of nylon Multifilament and lead line made of nylon, thermocole bundle or plastic drums (35l capacity) as floats; Stones / Steel iron (Irregular shape) used as sinkers were set in creek at the depth of 6–25 m around 2 am and hauled back around 7 am with a soaking duration of 3–4 h at each sampling date. In 15 fishing trails. Total length (TL) in cm was measured from the tip of the snout of the fish to the posterior tip of the caudal fin, to the nearest 0.1 cm by using a regular ruler validated against a vernier caliper. The corresponding total weight (TW) in g was measured using a digital balance with an accuracy of 0.1 g (Froese et al., 2014, 2017). The parameters (a= intercept and b= Slope) were estimated by the length‐weight relationship formula, W = a*Lb i.e., log W = log a + b log L, where, L is the total length, W is the total body weight, a and b are the intercept and slope of the power equation, respectively (Froese, 2006; Froese and Pauly, 2021).

A total of 3072 specimens belonging to 35 species, distributed under 7 orders, 21 families, and 29 genera, were recorded. The new maximum records (TL) of E. thoracata and B. mcclellandi is reported during the study. The results on the LWR estimates for the two studied species are presented in Tables I and II, providing for each species the sample size, size range covered as well as the means and 95% confidence intervals for both equation parameters a and b.

The information on LWR in fish is crucial for study on growth pattern-cum-behaviour, ecosystem health, trophic niche with habitat conditions, life history traits, and morphological characters of the fish (Froese, 2006). Our estimate for LWR equation ranges between 2.5 and 3.5 (Froese, 2006). The co-efficient of determination (R2) for the corresponding b value was estimated as 0.9263, Escualosa thoracata (Valenciennes, 1847) and 0.9612 Bregmaceros mcclellandi Thompson, 1840 indicating better predictive power and smaller dispersion of the data. Though, Gorai creek ecosystem is an important ecosystem that provides different ecosystem services for coastal people, literature review revealed only limited studies on the aspects of its biodiversity (Datta et al., 2010), checklist of flora and fauna, water quality assessment (Varshney et al., 2006), health status (Balasaheb et al., 2017; Kesavan et al., 2021) and other ecological studies (Jaiswar et al., 2007). The findings of the study are helpful in the management of the depleted fish stock with special reference to Unicorn cod. The LWR obtained for Bregmaceros mcclellandi Thompson, 1840 in the present study should be considered as tentative and needs further substantiation because despite the fact that our study offers a new maximum total length (TLmax), the number of specimens is to be increased for future validation and confirmation.

Lm, length at first maturity; Lmax, maximum length reported; Bayesian length-weight, length-weight relationship study, (a: intercept, b: slope). Model estimates/ global standards, (PD50, TS, R, V, PC, GCS, FS, TS); PD50, phylogenetic diversity index; TS, trophic status; R, resilience (H, High; Me, Medium; l, Low); V, vulnerability (H, High; Mo, Moderate; L, Low); PC, price category (VH, Very High; H, High, Me, Medium; L, Low; Un, Unknown); GCS, global conservation status; IUCN/CITES/CMS, NT-near threatened; LC, least concern; DD, data deficient; NE, not evaluated; FS, fisheries status (HC, Highly Commercial; C, Commercial; MC, Minor Commercial (A: Aquaculture potential, Aq: Aquarium Potential, B: Bait, F: Food, G: Gamefish)). HTS, human threat status; (H, Harmless; P, Poisonous; T, Traumatogenic; V, Venomous).

n, sample size; TL, total length; TW, total weight; a, intercept; b, slope; CI, Confidence intervals; R2, Co-efficient of determination; *Estimate is tentative.

This study was conducted under the theme of Ecosystem valuation and the part of the Ph.D. research work of the first author. All the authors wish to express gratitude to The Director, ICAR-Central Institute of Fisheries Education, Mumbai and The Vice-Chancellor, Tamil Nadu Dr. J. Jayalalithaa Fisheries University, Nagapattinam and The Dean, Fisheries College and Research Institute, Thoothukudi for providing the necessary facilities, in valuable suggestions and their support during the study. The authors also thank the fishermen of Gorai creek for their selfless cooperation during vessel operation, field trip and sample collection.

Funding was provided by ICAR-Central Institute of Fisheries Education, Mumbai by providing Ph.D. Fellowship (ID.No. FRM-PA8-07, USID No. U18MHO1001DF007).

The Institutional Review Board have given approval for the article through PME cell.

No live specimens were used in the present investigation.

All the authors have gone through the manuscript and agreed to submit the manuscript for publication.

The authors have declared no conflict of interest.