Causation of Saddleback Deformities in The Yellowfin Bream Acanthopagrus australis Fishery: Evidence of Physical Injury

Barry Pollock

doi:10.9734/ajfar/2020/v10i430188

Abstract

The yellowfin bream A. australis supports an important commercial net and angling fishery on the east coast of Australia. Saddleback, a deformity of the dorsal fin and profile, occurs in this species, with the occurrence of fish with saddleback being as high as 10% in some areas. The present study provides new information and analysis of causation of the saddleback deformity in the yellowfin bream fishery. Lateral line scale regeneration due to injury, and soft tissue abnormalities indicative of deep wounding are present in yellowfin bream with saddleback. X-ray images of the entire skeleton of specimens with saddleback were also examined. An unpublished government report on chemical residues in saddleback and normal yellowfin bream is appended and discussed. The absence of both chemical residues, and lack of other skeletal deformities in yellowfin bream with saddleback provide indirect evidence of physical injury as the cause of saddleback in this case. The role of discarding of meshed yellowfin bream, which are smaller than the legal minimum size, as causation of the saddleback deformity is evaluated.

Highlights

Saddleback in fish is an abnormality of the dorsal fin and profile, lacking one to all of the dorsal spines, accompanied by shape, number and position abnormalities of associated pterygiophores [1]
Those results, together with the findings that scale loss associated with the saddleback deformity occurred at the mid-size juvenile stage indicated that the saddleback deformity and associated abnormalities in yellowfin bream result from physical injuries
Lateral line fracture and lateral line regenerated scales are not present in the yellowfin bream lacking the saddleback deformity. These findings indicate that lateral line fracture and lateral line scale regeneration are associated with the saddleback deformity in yellowfin bream

Summary

Introduction

Saddleback in fish is an abnormality of the dorsal fin and profile, lacking one to all of the dorsal spines, accompanied by shape, number and position abnormalities of associated pterygiophores [1]. It found that the saddleback deformity was significantly less common in small juveniles compared with the larger juveniles Those results, together with the findings that scale loss associated with the saddleback deformity occurred at the mid-size juvenile stage indicated that the saddleback deformity and associated abnormalities in yellowfin bream result from physical injuries. The present study complements and extends the previous study by Pollock [15] It provides new information on the saddleback deformity in wild yellowfin bream, including a description of lateral line scale loss and a histological examination of soft tissues (dermis, connective tissue and muscle) at the saddleback deformity site. The present study provides information on the lack of chemical residues in tissues of deformed and normal yellowfin bream, an assessment of xray images of saddleback fish for other skeletal abnormalities, and a description of the commercial net fishery with an assessment of its role in saddleback causation

Methods

Findings

Discussion

Conclusion