Morphological investigation and length-weight relationships of long-snouted pipefish Doryichthys boaja (Syngnathidae) from two different environments

Abstract

Importance of the work: Stock identification is fundamental knowledge for fisheries biology and management of any fishing-targeted species.Objectives: To discriminate stocks of long-snouted pipefish Doryichthys boaja from lentic and lotic environments by using morphological characters.
Materials and Methods: Fish were collected from Songkhla Lake and Bangpakong River, Thailand. Sampled individuals were evaluated for weight, seven meristic characters, and 16 morphometric characters. Multivariate methods viz., permutational multivariate ANOVA, principal component analysis and linear discriminant function analysis were applied for stock discrimination. The length-weight relationship and condition factor were also examined.
Results: The sample of D. boaha comprised 297 individuals from Songkhla Lake and 110 from Bangpakong River. Permutational multivariate ANOVA revealed significant differences by sex and environment (p < 0.05). Except for tail length, morphometric and meristic characters all showed high loadings to the principal component axes. The linear discriminant function analysis predicted high accuracy in separating the two stocks. However, low success in prediction was found when using the meristic characters to distinguish the samples in combination of sex and environment. Results from the length-weight relationship indicate positive allometric growth of the stock from Songkhla Lake, and negative allometric growth for Bangpakong River; hence, the former appears healthier and with better growth.
Main finding: The morphometric characters provide a more accurate stock determination of D. boaja than the meristic characters. Difference in the length-weight relationship implies the effects by geographical and environmental conditions