Rearing diet may determine fish restocking success: a case study of hatchery-reared juvenile meagre, <em>Argyrosomus regius</em>

Abstract

Abstract:The resilience of released hatchery-reared specimens increases with age and size, but production costs are also greater for these individuals. Therefore, for a given budget, the consequences of increasing age and size impose a trade-off between producing a large number of vulnerable (small) fish or a small number of resilient (large) fish. Once the optimal size for releasing fish has been defined, the choice of rearing protocol will determine the number and quality of the fish that can be released. In this study, different rearing protocols were compared using meagre juveniles (Argyrosomus regius), which are presently the target of a restocking programme conducted in the Balearic Islands (western Mediterranean). Seven different diets were compared during the grow-out phase to identify the diets that produced good-quality juveniles of a given size at the lowest cost. Most of the diets produced juveniles of suitable biological quality in terms of growth, fish condition (relationships between length and total weight, liver weight and mesenteric fat weight) and tissue biochemical composition. A semi-moist diet (Diet G) provided the best growth rate, closely followed by commercial meagre pellets (Diet A). In contrast, the cost of growing fish with Diet A was lower for any possible size at release. This study demonstrates the need to consider both growth rate and production cost to select the rearing protocol that maximizes the number of juveniles that can be produced for a given budget and desired release size. These considerations will ultimately increase the chance of success of restocking programmes.Keywords: Argyrosomus regius; restocking programme; production cost; fish quality; diet.La dieta usada en la cría puede determinar el éxito en la repoblación de peces: el caso de juveniles de corvina Argyrosomus regius criados en cautividad Resumen: La resiliencia de los ejemplares criados en cautividad y liberados se incrementa con la edad y el tamaño, pero los costes de producción también aumentan. Por lo tanto, para un presupuesto dado, estas consecuencias del incremento de la edad y el tamaño imponen un compromiso entre la producción de un gran número de peces vulnerables (pequeños) o un pequeño número de peces resistentes (grandes y de más edad). Una vez que el tamaño óptimo para la liberación de peces se ha definido, la elección del protocolo de cría determinará el número y la calidad de los peces que se pueden liberar con un presupuesto dado. En este estudio, se comparó la aplicación de diferentes protocolos de cría a juveniles de corvina (Argyrosomus regius), que es la especie objetivo de un programa de repoblación llevado a cabo en las Islas Baleares (Mediterráneo occidental). Se compararon siete dietas diferentes durante la fase de engorde para identificar cuáles de ellas podrían producir juveniles de buena calidad, de un tamaño dado y al menor coste. La mayoría de las dietas produjeron juveniles de calidad biológica adecuada en términos de crecimiento, condición del pez (estimada a partir de la rela...

Many Vulnerable or a Few Resilient Specimens? Finding the Optimal for Reintroduction/Restocking Programs

“…The second simulation experiment is very similar, but the number of fish actually released depends on a fixed budget (here, 10,000 €/year). The higher the length at the time of release, the smaller the number of fish actually produced is [ 6 ], because the cost of production per fish ( CO ) increase nonlinearly with the length and age ( Fig 6 ). The releasing age that maximizes the number of survivors after one year at liberty was estimated at 1,173 days ( Fig 7 ), but only 17 fish (out of the 201 fish that can be produced and released with 10,000 €/year) would survive.…”

“…In the second simulation experiment, up to 100 sets of fish of increasing age (from 180 to 2,000 days old) were simulated, but in this case, the number of fish of each set is not fixed, but corresponds to the number of fish that can be produced with a given budget. The relationship between cost-per-fish ( CO ) and age/length takes into account feeding cost ( FCO ) and personal cost ( PCO ) [ 6 ]: …”

“…Where the feeding cost ( FCO ) depends on the price of the diet (€ kg −1 ) and the accumulated daily food ration (kg), which depends on the temperature, fish size and pellet size. The personnel cost per fish ( PCO ) depends on the salary per day ( S ), the number of fish finally produced in a given year and the days ( D ) required on each diet to achieve the desired length [ 6 ].…”

“…These programs are usually based on releasing juveniles because, although subject to higher mortality than adults, they are assumed to be less affected by captivity and more readily adaptable to the wild [ 4 , 5 ]. Moreover, producing juveniles is economically more efficient [ 6 , 7 ].…”

Effect of Stocking Density on Growth Performance, Production Trait, Food Utilization and Body Composition, of Meagre (Argyrosomus regius)

“…Beside water quality, the effect of stocking density on meagre fingerlings might be dependent upon the biological characteristics of fish, such as tolerance to environmental change, life stage, sex, social interaction and behavior, so that density effect on growth and production might be explained by their competition for territories [20]. The stress on fish caused by crowdedness may be other explanation for the effect of stocking density.…”