Quality Descriptors and Predictors in Farmed Marine Fish Larvae and Juveniles (original) (raw)

2018, Larval Fish Production,

Executive Summary Background Factors such as feed composition and water temperature during the early larval stages, as well as the fish genetic line, have major impact on fish larvae and juveniles quality. Some of these effects are only easily noticeable later in the juvenile stage. Therefore it is important to develop appropriate criteria / indices for the description and prediction of fish quality. Larval and juvenile external appearance, histology and analysis of the skeleton by X-ray have been widely used as such quality indices. Sorting of fish with severe anomalies has been successfully applied at the hatchery level, but only when juveniles reach a few grams. Still this causes significant economic losses, and not all fish with anomalies are identified. Moreover, external morphology is only part of fish quality. Other aspects such as gamete quality, nutritional condition, growth potential at later stages, immune competence and gut microbiology are paramount in defining quality of juvenile and adult fish. Still, little progress has been so far accomplished on identification and validation of early predictors/descriptors of fish quality. Such indices should ideally estimate quality as early as possible in larvae life, with high accuracy and precision, with fast and simple methodologies, and at low cost. Principal Findings and Conclusions Currently, available precise indices are few and limited to the prediction of fish quality in terms of some aspects of morphology alone. Existing literature clearly suggests that the development of indices for the prediction of fish quality in terms of normal larval development, growth potential, immune and nutritional condition will soon be possible, by exploiting the rapidly growing knowledge on different aspects of fish larvae development. Still, this quality assessment needs to be relatively simple and at a reasonable cost so it can be routinely applied in fish farms. Probably such a set of practical quality indices with predicting All rights reserved. power should include a combination of morphology characteristics and expression of selected genes. Scientific Significance This review provides a framework for the future development of a science-based set of practical quality indices that can predict larval and juvenile quality. Promising candidates include: morphology characteristics that establish a clear correlation of larval/early juvenile and market-size fish external appearance; expression of genes for bone development, i.e., TRAP, osteocalcin and alkaline phosphatase; nutrition condition descriptors such as gut histology, as well as gene expression genes of genes coding for digestive enzymes; indices of growth potential, such as muscle fibre number and size, and expression of genes related to muscle growth, e.g, MRFs, GH, IGFs, MAPK, and growth-related QTLs; gamete quality descriptors such as sperm motility/viability/ATP levels, early egg cleavage pattern, blastomere morphology and maternal gene transcripts; descriptors of immune condition such as immunoglobulin M and IgT/Z levels for systemic and mucosal responses respectively, and disease challenge tests. Practical Application It is expected that indices for the prediction of fish quality in terms of high survival, normal appearance, growth potential, the ​immune and nutritional condition will be available in the future. However, this will require a concerted R&D effort from researchers and producers, focusing on the validation of such indices at the commercial scale.