Impacts of rearing techniques on growth, survival and bacterial microbiota of carpet shell clam (Ruditapes decussatus) larvae

Amel Medhioub,Sondes Bchir,Mohamed Nejib Medhioub,Mahjoub Aouni,Wissem Slimani,Badreddine Mechri,Younes Limeyem

doi:10.1007/s10499-016-0055-4

Abstract

In this study, we investigate the impacts of two water treatment regimes, the closed aquaculture system (CAS) and flow-through system (FTS), on the carpet shell clam (Ruditapes decussatus) larval microbiota, growth and survival. A bacteriological barrier (B) was created among breeder stage treated by florfenicol (FF, 8 mg L−1day−1 per 5 days). After spawning, larvae were maintained in five different rearing techniques: CAS; FTS; B + CAS; B + FTS and B + CAS + FF (8 mg L−1 day−1 per 3 days). Significant decrease was observed in both total bacterial count and presumptive Vibrio count (PVC) in FF-treated breeders. Besides, larvae reared in B + FTS showed significantly lower PVC than larvae maintained in other rearing techniques. It was also determined that growth and survival of larvae reared in B + CAS + FF and B + FTS were significantly better than those reared in other systems. One hundred and twelve Vibrio strains, isolated from breeders, eggs and larvae, were subjected to some bacteriological tests (API 20E strips, vibriostatic agent O/129, growth at different temperatures and salinity). Vibrio alginolyticus was the predominant isolated species (36.61 %), followed by V. fluvialis (25 %), V. vunificus (17.86 %), V. cholera (13.39 %) and V. paraheamolyticus (7.14 %). These results may contribute to the understanding of the effect of rearing techniques on the bacterial load, survival and growth of early life stages of R. decussatus larvae.

Highlights

The carpet shell clam, Ruditapes decussatus (Linnaeus 1758), is the most abundant and commercially important species of Veneridae in different North African estuaries and lagoons
In this study, we investigate the impacts of two water treatment regimes, the closed aquaculture system (CAS) and flow-through system (FTS), on the carpet shell clam (Ruditapes decussatus) larval microbiota, growth and survival
The bacteriological control of R. decussatus reproducer showed in all three ponds treated with FF, a significant decrease (P \ 0.05) in total viable counts (TVC) in Marine agar (Ma) medium (Pond1, T0: 1.80 9 109 - T96: 3.00 9 CFU g-1) as well as in presumptive Vibrio counts (PVC) in TCBS medium (Pond1, T0: 6.10 9 - T96: 5.00 9 102 CFU g-1)

Summary

Introduction

The carpet shell clam, Ruditapes decussatus (Linnaeus 1758), is the most abundant and commercially important species of Veneridae in different North African estuaries and lagoons. In Tunisia, it is found predominantly in the Gulf of Gabes (Medhioub 1983) and its collecting represents a traditional activity that has a significant socioeconomic impact in terms of both income and employment The development of this economic sector involves the rational management of beds and the breeding of this species, which requires mass production of juveniles. To this aim, several basic and applied research programs have been conducted to develop new techniques for improvement in R. decussatus larval and post-larval reared in the experimental bivalve hatchery of the National Institute of Marine Sciences and Technology. Despite the use of antibacterial agents as prophylactic therapy, we have been confronted with recurrent epizootic disease outbreaks in larval and early post-larval stages, causing high mortality (Mechri et al 2015)

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