In a context of high occupation of the coastal area, we studied this occupation impact measuring developmental stability of post-larvae and juveniles (Oblada melanura in nursery zones and Dicentrarchus labrax in aquariums). We intend to provide information for the management of these aquaculture and seaside resort zones. We expect to create a new mid/long-term stress indicator using otolith Fluctuating Asymmetry (FA).

news asymetrie fluctuante 01

Figure 1 : 79 Days old D. Labrax sagittae.
Foto: Pierre Vandenbussche 2013

FA is used to measure bilateral individual developmental stability. Departure from symmetry is described by frequency distribution of right minus left part. In case of FA this frequency distribution should be a Normal curve centred around 0 (Palmer 1994). If stress occur, this Normal curve tend to present an augmentation of the kurtosis (a perfect Normal law present a ketosis of 0).

news asymetrie fluctuante 02

Figure 2: FA ideal distribution, right curve present a bigger kurtosis sign of a higher level of FA.
From Palmer 1994

In order to obtain FA information, we use an intern-ear hard structure called otolith. Fish present 3 pairs of otolith. Those otoliths are used by fish for earing and space recognition. They are called sagittae, lappili, asterisci. We use the sagittae pair in our works.

We chose this structure for 3 reasons:

First, it presents, like a pearl, a successive ring structure which is easily recognisable on microscopy. This is due to the way it is formed. Every day a new ring, or increment, (Chambers and Miller 1995) is deposited. So if a change occurs in the fish environment, traces of this change will appear on the concerned ring (Arai, Ohji et al. 2007).

Second, the sagittae pair is generally the biggest of the three otolith pairs and so can be collected more easily. It also reduces the risk of misinterpretation during analyses.

Third, we use otolith because it’s an internal structure, meaning there is less risk of deterioration during sampling time.

This Precaution was really important because of the use of post-larvae and juveniles. At this early life stage fish are really fragile. As sampling method could damages the external part of fish the utilisation of external symmetric traits is impossible.

Arai, T., M. Ohji, et al. (2007). "Trace Metal Deposition in Teleost Fish Otolith as an Environmental Indicator." Water Air Soil Pollut(179): 255-263.

Chambers, R. C. and T. J. Miller (1995). Evaluating Fish Growth by Mean of Otolith Increment Analysis: Special Proprieties of Individual-level Longitudinal Data. Recent Development in Otolith Research, Columbia, South Carolina, United States of America, University of South Carolina Press.

Palmer, A. R. (1994). Fluctuating asymmetry analyses: A primer. Developmental Instability: Its Origins and Evolutionary Implications, Tempe, Arizona, Springer Netherlands.