Abstract
Simple SummaryFish skeletal development and incidence of skeletal deformities are important factors to warrant aquaculture success. Skeletal deformities reduce fish viability, growth, and feed efficiency but also degrade the consumer’s perception of aquaculture products. Some skeletal deformities would also decrease animal wellbeing. Tench (Tinca tinca) is a freshwater species cultured in ponds, highly demanded in particular regions of Europe and a promising species for aquaculture diversification. Determining the onset of the different skeletal structures may help fish farmers to adapt and improve rearing practices (e.g., water temperature, feeds composition, etc.) to decrease the incidence of skeletal deformities. At the same time, monitoring the incidence of skeletal deformities represents a valuable decision-making tool to improve efficient use of facilities and resources.Skeletal deformities reduce fish viability, growth, wellbeing, and feed efficiency but also degrade the consumer’s perception of aquaculture products. Herein, the skeletal development and the incidence of skeletal deformities in tench (Tinca tinca) reared in semi-extensive conditions has been described in detail for the first time. Larval skeletons were assessed through an acid-free double-staining procedure in 157 individuals, while 274 specimens at the juvenile stage were evaluated through X-ray analysis. The first skeletal structures to be formed were those related with breathing and feeding activities (e.g., Meckel’s cartilage and opercula) and were visible in larvae of 4 mm of standard length (SL). The axial skeleton was fully ossified in larvae of 12–17 mm of SL, and the caudal fin complex in larvae with 17–26 mm of SL. At the larval stage, no upper-jaw or opercula deformities were observed, while a low incidence (1–9%) of other severe deformities in the heads of the fish (e.g., lower-jaw deformities) were reported. The incidence of vertebral deformities in tench reared in natural ponds was considerable in larvae (54%) and juveniles (52%). Vertebral deformities (fusion and compression) were the most common deformities found in tench larvae (approximately 30%) and vertebral shape deformity in juveniles (around 10%), being mainly located in the caudal region. Thus, a regular monitoring of the skeletal deformities in tench might help to identify better rearing protocols and improve product quality sold at markets. Characterizing the skeletal development not only in semi-extensive systems such as artificial and natural ponds but also under intensive rearing conditions, seems vital for a sustainable and profitable European tench aquaculture.
Highlights
Tench (Tinca tinca Linneo, 1758) is a freshwater epibenthic cyprinid hypothesized to be native in most of European countries
Skeletal formation in tench progressed very rapidly, with first elements mineralizing at 4 mm (5 dpf) and the skeleton being almost completed at 26 mm (85 dpf)
A considerable incidence of deformities (54.1% and 52.2%) was determined using both analytical approaches in tench when reared in natural ponds
Summary
Tench (Tinca tinca Linneo, 1758) is a freshwater epibenthic cyprinid hypothesized to be native in most of European countries. In Eastern European countries, it is reared in ponds and sold at a weight of over 500 g. In particular regions of Southern European countries (Spain and Italy), it is a highly demanded and valued (between 16–18 € kg−1) gastronomic product at lower size (80–120 g), being traditionally reared in extensive monoculture natural ponds [2]. European production has decreased from more than 5000 to 2400 tons during the last decade, with France, Russia, Poland, Germany, the Czech Republic, and Spain being the major producers [5]. In Spain, production has been reduced, hypothetically due to a significant reduction of wetlands by successive dry events, the lowering of water quality in natural ponds, and/or the constant loss of population in rural areas. Implementing regular monitoring procedures as decision-making tools for fish farmers is urgently required to assess whether a rearing protocol or a fish batch should be optimized or discarded, respectively
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