Development of free neuromasts in Engraulis ringens and Strangomera bentincki (Teleostei, Clupeiformes) early larvae

Alejandra Llanos Rivera,Eduardo Tarifeno,Leonardo R Castro,Guillermo Herrera

doi:10.3856/vol42-issue1-fulltext-22

Abstract

Neuromast morphology and distribution are characterized during early ontogeny of anchoveta (Engraulis ringens) and common sardine (Strangomera bentincki). Although both species share morphological features, they show several differences during their early ontogeny, such as size at hatching and yolk absorption. Larvae were obtained from incubation of planktonic eggs (at 12°C), collected during the spawning season 2001 (August-September) at Coliumo Bay. The neuromasts were observed from hatching to 25 days, and the pattern of neuromast appearance, in newly hatched larva, until yolk absorption, was determined using Janus Green staining and scanning electronic microscope. Results showed a similar pattern of neuromast development in both species. At hatching, two pairs of neuromasts were observed in the cephalic area and 8-9 in the rest of the body, which increased to 19 pairs and to 30-39 pairs at a larval size of 11 mm, respectively. On the average, 12 hair cells per neuromast were counted, with little variation among neuromasts. The polarity of these hair cells was closest to multiple polarity. Neuromast positioning for both species, anchoveta and common sardine larvae, are similar to those of Engraulis mordax and Clupea harengus, respectively. The similar development pattern of these species seems to be related to similar functional constraints and close taxonomic affinity.

Highlights

The pattern of neuromast development is affected by the relative importance of mechanical perception (e.g., Blaxter & Fuiman, 1990; Mukai et al, 1994), in particular, the onset of vision and other sensory systems, which differs between species
There is no information about neuromast in the larvae of these two species, except for the observation of small mechanoreceptor protuberances located along the sides of the body in larval anchoveta by Fischer (1958)
The hypothesis that early larvae of S. bentincki develop a more complex neuromast system for mechanical perception to feed on mobile prey will be tested

Summary

Introduction

A comparative analysis of neuromast development between these two species, which share a similar larval morphology, might help to explain the observed ontogenetic differences. The development of free neuromasts during the early ontogeny (hatching to early postflexion) was characterized in anchoveta and common sardine, in terms of number, position, sequence of appearance, length of cupulae, number of hair cells, and polarity. Anchoveta and common sardine hatched with a complement of two cephalic pairs of neuromasts anterior to the otic capsules, plus 7-8 pairs on the trunk (Fig. 1a).

Results

Conclusion