ABSTRACT
RATIONALE: Carbon and nitrogen stable isotope analyses of fish tissues are now commonly used in ecological studies but mostly require the sacrifice of the animal. Ethical considerations recommend the use of anesthetics for tissue sampling. This study examines how anesthetics affect stable isotope ratios of fish compared with other euthanasia methods. METHODS: Rainbow trout fry and juveniles were sacrificed using ice-freezing (as this common method used to kill fish does not affect natural isotopic ratios), electronarcosis or an overdose of chemical anesthetics (2-phenoxyethanol, benzocaine and clove oil). For fry, we sampled the whole animal whereas, for juveniles, white dorsal muscle, liver, red blood cells, plasma, external tegument and pectoral fin were sampled. Isotopic ratios and the elemental compositions of carbon and nitrogen were then measured. RESULTS: The δ15 N values, and the C and N contents of all considered tissues as well as δ13 C values of muscle, liver, red blood cells and plasma, were not affected by the use of chemical anesthetics. Clove oil and to a lesser extent 2-phenoxyethanol and benzocaine decreased δ13 C values of whole fry and juvenile external tegument and pectoral fin. The use of electronarcosis drastically affects the δ13 C and δ15 N values of all fish tissues. CONCLUSIONS: Anesthetics should be avoided for δ13 C analysis when tissues are in contact with the water containing the anesthetic. Ice-immersion has to be preferred when approved by guidelines. If not, benzocaine and 2-phenoxyethanol should be preferred over clove oil. Electronarcosis should not be used to kill fish until further investigations are performed.
Subject(s)
Carbon Isotopes/analysis , Nitrogen Isotopes/analysis , Oncorhynchus mykiss/metabolism , Animals , Carbon Isotopes/metabolism , Euthanasia , Freezing , Mass Spectrometry , Nitrogen Isotopes/metabolismABSTRACT
Within the context of a growing aquaculture production coupled with a plateau of the production in the main components of aquafeeds (fish oil and fishmeal), recent studies have typically focused on replacing these feedstuffs with terrestrial plant ingredients for cultured carnivorous aquatic species, such as rainbow trout (Oncorhynchus mykiss). Substitution rates without adverse effects have, however, reached their limit. One potential way forward would be to take advantage of the genetic variability that exists in the salmonid population. However, to date, little is known about the underlying molecular mechanisms responsible for this genetic variability. The aim of the present research was to understand why some genotypes are better able to utilize plant-based diets devoid of marine resources. In this regard, three isogenic lines of rainbow trout (R23h, AB1h, and A22h), with similar growth when fed marine resources-based diets and which differ greatly in their responses to a plant-based diet, were fed with either a complete plant-based diet (V diet) or a marine resources-based diet (M diet) since first-feeding. Fish traits and the hepatic transcriptome of these three genotypes were compared after 5 months of feeding. First, differences in the ability to grow with the V diet observed amongst genotypes was not due to higher feed intake, but instead due to differences in feed efficiency. The comparison of transcriptome profiles revealed 575 (R23h vs. AB1h), 1,770 (R23h vs. A22h), and 2,973 (AB1h vs. A22h) probes differentially expressed amongst the three genotypes when fed the V diet. Interestingly, R23h and AB1h fish, which were the least affected by the V diet, exhibited the highest growth. These results demonstrate that these fish were able to maintain a high level of energy production and protein synthesis. Moreover, these genotypes were also able to activate pathways linked to lipid and cholesterol metabolisms, such as the biosynthesis of long-chain polyunsaturated fatty acids. Finally, as previously, immunity seems to also play an important role in the ability of fish to use the V diet, and further studies are needed to understand the mechanisms by which immunity interacts with growth.
ABSTRACT
In the context of limited marine resources, the exponential growth of aquaculture requires the substitution of fish oil and fishmeal, the traditional components of fish feeds by terrestrial plant ingredients. High levels of such substitution are known to negatively impact fish performance such as growth and survival in rainbow trout (Oncorhynchus mykiss) as in other salmonids. In this respect, genetic selection is a key enabler for improving those performances and hence for the further sustainable development of aquaculture. We selected a rainbow trout line over three generations for its ability to survive and grow on a 100% plant-based diet devoid of both fish oil and fishmeal (V diet) from the very first meal. In the present study, we compared the control line and the selected line after 3 generations of selection, both fed either the V diet or a marine resources-based diet (M diet). The objective of the study was to assess the efficiency of selection and the consequences on various correlated nutritional traits: feed intake, feed efficiency, digestibility, composition of whole fish, nutrient retention and fatty acid (FA) profile. We demonstrated that the genetic variability present in our rainbow trout population can be selected to improve survival and growth. The major result of the study is that after only three generations of selection, selected fish fed the V diet grew at the same rate as the control line fed the M diet, whilst the relative reduction of body weight was 36.8% before the selection. This enhanced performance on the V diet seems to be mostly linked to a higher feed intake for the selected fish.
Subject(s)
Animal Feed , Fish Oils , Fishes , Oncorhynchus mykiss/growth & development , AnimalsABSTRACT
The purpose of this work was to determine the optimal protein level to feed alevins of coporo (Prochidolus mariae) fish. Four diets were formulated with growing levels of crude protein (15, 25, 35 and 45%) with similar energy values (between 19,6 and 20,4 KJ g-1). Three trials were performed for each diet. The animals were acclimated and fed a commercial diet during one week and after that time the test diets were administered ad libitum three times a day during 41 days. Fifty five frys per fishbowl were placed with an initial mean weight of 0,32 ± 0,04 g. Three periods of fourteen days each were registered and at the end of each period weight gain (GP) and food consumption per fish tank was determined. The zootechnical parameters, final mean weights (PMF), total weight gain (GTP), specific growth rate (TCE) and daily growth index (ICD) of the fish did not show significant differences between the diets with protein levels of 35% and 45% proteins, indicating that a diet with 35% protein is adequate for a good development of the fish in this stage.
El propósito de este trabajo fue determinar el óptimo proteico en la alimentación de alevines de coporo (Prochidolus mariae). Se formularon 4 dietas con niveles crecientes de proteína cruda (15, 25, 35 y 45%), y valores energéticos similares entre 19,6 y 20,4 KJ g-1, de manera que sean isocalóricas. Se realizaron tres repeticiones por cada dieta (n=3). Los alevines fueron aclimatados y alimentados con una dieta comercial durante una semana y luego de este tiempo se le suministraron las dietas a ensayar ad libitum tres veces al día durante 41 días. Se colocaron 55 alevines por pecera con peso medio inicial de 0,32g ± 0,04. Se llevó un registro durante tres períodos, de catorce días cada uno, al final de cada período se determinó la ganancia de peso (GP) y el consumo de alimento por pecera. Los parámetros zootécnicos, pesos medios finales (PMF), ganancia total de peso (GTP), tasa de crecimiento específico (TCE) e índice de crecimiento diario (ICD) de los peces, no presentaron diferencias significativas entre las dietas con 35 y 45% de proteínas, lo que indica que una dieta con 35% de proteínas, es adecuada para un buen desarrollo del pez en este estadio.
Subject(s)
Animals , Proteins , Diet , Diet , FishesABSTRACT
The primary objective of this investigation was to determine the apparent digestibility coefficient (ADC) of earthworm flour (EW) and compare it with other raw feeding materials already evaluated like wheat bran (BW) and soy cake (CS) in the feeding of the rainbow trout (Oncorhynchus mykiss). Fifteen trout of an average weight of 100 g were placed in duplicate tanks provided with an automated fecal material collecting system. CS and EW flour showed a protein ADC of 90.1% and 90.0%, respectively, when comparing them with BW (57.2%). Energy ADC was superior in CS (75.4 KJ/g) and EW (72.5 KJ/g). The values of the percentage of digestible protein were superior in the EW (63.4%) in comparison with CS (48.3%) and AT (8.8%); digestible energy was superior in EW (17.1 KJ/g) followed by CS (14.9 KJ/g) and AT (2.4 KJ/g). We conclude that the EW flour has an excellent protein and energy digestibility.
El objetivo principal de esta investigación fue determinar el coeficiente de digestibilidad aparente (CUDa) de la harina de lombriz (HL) y compararla con otras materias primas ya evaluadas, como el afrecho de trigo (AT) y torta de soja (TS) en la alimentación de truchas arco iris (Oncorhynchus mykiss). Esta experiencia se realizó con 15 individuos por tanque en duplicados, con un peso promedio de 100 g, conectados a un sistema automático de recolección de heces. Las harinas de TS y HL presentaron un CUDa proteica de 90,1 % y 90 %, respectivamente, al compararlas con la del afrecho de trigo (57,2 %). El CUDa energético fue superior en la TS (75,4 KJ/g) y HL (72,5 KJ/g). Los valores del porcentaje de proteína digerible fueron superiores en la HL (63,4 %); en comparación con la TS (48,3 %) y AT (8,8 %). Con respecto a la energía digerible fue del mismo modo superior en la HL (17,1 KJ/g), seguido por la TS (14,9 KJ/g) y el menor valor para el AT (2,4 KJ/g). Se concluye que la harina de lombriz posee un valor elevado de digestibilidad proteica y energética.