Restructured products from tilapia industry by products: the effects of tapioca starch and washing cycles

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Depletion study and estimation of the withdrawal period for oxytetracycline in tilapia cultured in Brazil

Defining pharmacokinetic parameters and depletion intervals for antimicrobials used in fish represents important guidelines for future regulation by Brazilian agencies of the use of these substances in fish farming. This article presents a depletion study for oxytetracycline (OTC) in tilapias (Orechromis niloticus) farmed under tropical conditions during the winter season. High performance liquid chromatography, with fluorescence detection for the quantitation of OTC in tilapia fillets and medicated feed, was developed and validated. The depletion study with fish was carried out under monitored environmental conditions. OTC was administered in the feed for five consecutive days at daily dosages of 80 mg/kg body weight. Groups of ten fish were slaughtered at 1, 2, 3, 4, 5, 8, 10, 15, 20, and 25 days after medication. After the 8th day posttreatment, OTC concentrations in the tilapia fillets were below the limit of quantitation (13 ng/g) of the method. Linear regression of the mathematical model of data analysis presented a coefficient of 0.9962. The elimination half- life for OTC in tilapia fillet and the withdrawal period were 1.65 and 6 days, respectively, considering a percentile of 99% with 95% of confidence and a maximum residue limit of 100 ng/g. Even though the study was carried out in the winter under practical conditions where water temperature varied, the results obtained are similar to others from studies conducted under controlled temperature.

The fatty acid profiles and energetic substrates of two Nile tilapia (Oreochromis niloticus, Linnaeus) strains, Red-Stirling and Chitralada, and their hybrid

Protein and lipid content as well as the fatty acid (FA) composition of storage tissues were analysed in two varieties of Oreochromis niloticus (Red-Stirling and Chitralada) and their hybrid. The animals were maintained in cages for 11 months. The samples were taken when the animals weighed 10, 50, 100, 250 and 500 g. The results showed that changes in the metabolic processes occur during an increase in body mass in both varieties of tilapia and also their hybrid, but that these differences are not found in animals collected at the commercial weight. The protein content of the fillet and liver decreased with growth and the same protein content associated with growth was found for fillet lipid content. The genetic variety did not influence the FA profile of the fillet, but different genotypes had different hepatic FA compositions. Even with the same lipid content, the hepatocytes of Chitralada accumulated higher levels of polyunsaturated fatty acids (PUFA) n6 in triglycerides and increased C22:6n3 in the hepatocyte membranes. The higher n6PUFA content was compensated by a lower fraction of saturated FA in the hepatocyte triglycerides. The skin of Chitralada also had higher n6PUFA and C22:6n3 contents, suggesting a higher ability to deposit PUFA in the skin due to alterations in the liver synthetic pathway.

Effects of trophic levels (chlorophyll and phosphorous content) in three different water bodies (urban lake, reservoir and aquaculture facility) on gill morphology of Nile tilapia (Oreochromis niloticus)

Histological and ultrastructural analyses of gills were observed in Nile tilapia collected from three different waterbodies in southeast Brazil: an urban lake in a park in the city of São Paulo, a reservoir in a rural city, and a commercial aquaculture facility. These aterbodies were analyzed and classified as hypereutrophic, eutrophic, and supereutrophic, respectively, with 310.00, 94.00, 28.00 of phosphate (PO2_ 4 lg L _1) and 65.49, 24.95, 12.83 of chlorophyll (lg L _1). A significant difference in the histological alterations index (HAI) was observed only in fish from the urban lake, with the presence of cell hypertrophy, hyperplasia, aneurism, and other alterations. When compared to the other groups, a large quantity of rodlet cells was also observed in the urban group. These results demonstrate the correlation of eutrophic states of water with gill morphology. Also discussed is the premise that large amounts of organic material dissolved in water can alter the morphology of the fish gills

Spatial and temporal variation in population genetic structure of wild Nile tilapia (Oreochromis niloticus) across Africa

Background: Reconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (Oreochromis niloticus) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales. Results: Using nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (R(ST) = 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (R(ST) = 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (R(ST) = 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (F = 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m similar to 0.094 - 0.097) in the Volta populations. Conclusions: This study revealed clear hierarchical patterns of the population genetic structuring of O. niloticus in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.

Differential expression of IGF-I mRNA and peptide in the male and female gonad during early development of a bony fish, the tilapia Oreochromis niloticus

Insulin-like growth factor I (IGF-I) plays a key role in the complex system that regulates bony fish growth, differentiation, and reproduction. The major source of circulating IGF-I is liver, but IGF-I-producing cells also occur in other organs, including the gonads. Because no data are available on the potential production sites of IGF-I in gonad development, developmental stages of monosex breedings of male and female tilapia from 0 day postfertilization (DPF) to 90 DPF were investigated for the production sites of IGF-I at the peptide (immunohistochemistry) and mRNA (in situ hybridization) level. IGF-I mRNA first appeared in somatic cells of the male and female gonad anlage at 7 DPF followed by IGF-I peptide around 9-10 DPF. Gonad anlagen were detected from 7 DPF. Starting at 7 DPF, IGF-I peptide but no IGF-I mRNA was observed in male and female primordial germ cells (PGCs) provided that IGF-I mRNA was not under the detection level, this observation may suggest that IGF-I originates from the somatic cells and is transferred to the PGCs or is of maternal origin. While in female germ cells IGF-I mRNA and peptide appeared at 29 DPF, in male germ cells both were detected as late as at 51-53 DPF. It is assumed that the production of IGF-I in the germ cells is linked to the onset of meiosis that in tilapia ovary starts at around 28 DPF and in testes at around 52-53 DPF. In adult testis, IGF-I mRNA and peptide occurred in the majority of spermatogonia and spermatocytes as well as in Leydig cells, the latter indicating a role of IGF-I in the synthesis of male sex steroids. In adult ovary, IGF-I mRNA and IGF-I peptide were always present in small and previtellogenic oocytes but only IGF-I peptide infrequently occurred in oocytes at the later stages. IGF-I expression appeared in numerous granulosa and some theca cells of follicles at the lipid stage and persisted in follicles with mature oocytes. The results suggest a crucial role of local IGF-I in the formation, differentiation and function of tilapia gonads.

Sex determination and temperature-induced sex differentiation in three natural populations of Nile tilapia (Oreochromis niloticus) adapted to extreme temperature conditions

As a species of major interest for aquaculture, the sex determination system (SDS) of Nile tilapia, Oreochromis niloticus, has been widely investigated. In this species, sex determination is considered to be governed by the interactions between a complex system of genetic sex determination factors (GSD) and the influence of temperature (TSD) during a critical period. Previous studies were exclusively carried out on domestic stocks with the genetic and maintenance limitations associated. Given the wide distribution and adaptation potential of the Nile tilapia, we investigated under controlled conditions the sex determination system of natural populations adapted to three extreme thermal regimes: stable extreme environments in Ethiopia, either cold temperatures in a highland lake (Lake Koka), or warm temperatures in hydrothermal springs (Lake Metahara), and an environment with large seasonal variations in Ghana (Kpandu, Lake Volta). The sex ratio analysis was conducted on progenies reared under constant basal (27 degrees C) or high (36 degrees C) temperatures during the 30 days following yolk-sac resorption. Sex ratios of the progenies reared at standard temperature suggest that the three populations share a similar complex GSD system based on a predominant male heterogametic factor with additional influences of polymorphism at this locus and/or action of minor factors. The three populations presented a clear thermosensitivity of sex differentiation, with large variations in the intensity of response depending on the parents. This confirms the presence of genotype-environment interactions in TSD of Nile tilapia. Furthermore the existence of naturally sex-reversed individuals is strongly suggested in two populations (Kpandu and Koka). However, it was not possible here to infer if the sex-inversion resulted from minor genetic factors and/or environmental influences. The present study demonstrated for the first time the conservation of a complex SDS combining polymorphic GSD and TSD components in natural populations of Nile tilapia. We discuss the evolutionary implications of our findings and highlight the importance of field investigations of sex determination. (c) 2007 Elsevier B.V. All rights reserved.

Tilapia sex determination: Where temperature and genetics meet

This review deals with the complex sex determining system of Nile tilapia, Oreochromis niloticus, governed by the interactions between a genetic determination and the influence of temperature, shown in both domestic and wild populations. Naturally sex reversed individuals are strongly suggested in two wild populations. This can be due to the masculinising temperatures which some fry encounter during their sex differentiation period when they colonise shallow waters, and/or to the influence of minor genetic factors. Differences regarding a) thermal responsiveness of sex ratios between and within Nile tilapia populations, b) maternal and paternal effects on temperature dependent sex ratios and c) nearly identical results in offspring of repeated matings, demonstrate that thermosensitivity is under genetic control. Selection experiments to increase the thermosensitivity revealed high responses in the high and low sensitive lines. The high-line showed ~ 90% males after 2 generations of selection whereas the weakly sensitive line had 54% males. This is the first evidence that a surplus of males in temperature treated groups can be selected as a quantitative trait. Expression profiles of several genes (Cyp19a, Foxl2, Amh, Sox9a,b) from the gonad and brain were analysed to define temperature action on the sex determining/differentiating cascade in tilapia. The coexistence of GSD and TSD is discussed.

Morphological evaluation of spermatogenesis in Lake Magadi tilapia (Alcolapia grahami): a fish living on the edge

Spermatogenesis in Lake Magadi tilapia (Alcolapia grahami), a cichlid fish endemic to the highly alkaline and saline Lake Magadi in Kenya, was evaluated using light and transmission electron microscopy. Spermatogenesis, typified by its three major phases (spermatocytogenesis, meiosis and spermiogenesis), was demonstrated by the presence of maturational spermatogenic cells namely spermatogonia, spermatocytes, spermatids and spermatozoa. Primary spermatogonia, the largest of all the germ cells, underwent a series of mitotic divisions producing primary spermatocytes, which then entered two consecutive meiotic divisions to produce secondary spermatocytes and spermatids. Spermatids, in turn, passed through three structurally distinct developmental stages typical of type-I spermiogenesis to yield typical primitive anacrosomal spermatozoa of the externally fertilizing type (aquasperm). The spermatozoon of this fish exhibited a spheroidal head with the nucleus containing highly electron-dense chromatin globules, a midpiece containing ten ovoid mitochondria arranged in two rows and a flagellum formed by the typical 9 + 2 microtubule axoneme. In addition, the midpiece, with no cytoplasmic sheath, appeared to end blindly distally in a lobe-like pattern around the flagellum; a feature that was unique and considered adaptive for the spermatozoon of this species to the harsh external environment. These observations show that the testis of A. grahami often undergoes active spermatogenesis despite the harsh environmental conditions to which it is exposed on a daily basis within the lake. Further, the spermiogenic features and spermatozoal ultrastructure appear to be characteristic of Cichlidae and, therefore, may be of phylogenetic significance.

The Efficacy of a Novel Microbial 6-Phytase Expressed in Aspergillus oryzae on the Performance and Phosphorus Utilization of Cold- and Warm-Water Fish: Rainbow Trout, Oncorhynchus mykiss , and Nile Tilapia, Oreochromis niloticus

The efficacy and tolerance of a novel microbial 6-phytase were investigated in rainbow trout, Oncorhynchus mykiss, and Nile tilapia, Oreochromis niloticus. Reference diets were sufficient in available phosphorus (P). The test diet limiting in available P was supplemented with phytase at 500, 1000, or 2000 phytase units/kg feed. The enzyme was effective in increasing total P apparent digestibility coefficient in relation to increasing the dose of phytase in rainbow trout and Nile tilapia. Zinc apparent digestibility improved in relation to phytase supplementation in rainbow trout. P release due to phytase supplementation ranged from 0.06 to 0.18% P/kg feed in rainbow trout and from 0.13 to 0.26% P/kg feed in Nile tilapia. A 58-d performance trial was conducted to evaluate tolerance of fish to phytase supplementation. Dietary treatments consisted of a basal diet without phytase or supplemented with 2000 and 200,000 phytase units/kg feed. Results indicate that this novel microbial 6-phytase is well tolerated by fish. Significant improvements for growth as well as feed conversion ratio were observed when the phytase was fed at 2000 phytase units/kg feed. This phytase is proven efficient in releasing P from phytate and could be added when plants are used for fish meal replacement in diets for salmonid and omnivorous fish.

Occurrence of the Oribatid Mite Trhypochthoniellus longisetus longisetus (Acari: Trhypochthoniidae) on Tilapia (Oreochromis niloticus).

Mites as parasites infesting fish have been described in a few case reports involving Histiostoma anguillarum, H. papillata, and Schwiebea estradai. We describe the unexpected occurrence of oribatid mites of the genus Trhypochthoniellus on farmed tilapia Oreochromis niloticus. The fish had mites on the skin, fins, and gills, as well as in the mouth. The morphological characteristics of the mites, observed by optical and scanning electron microscopy, were consistent with those described for T. longisetus longisetus. All stages of development were observed, suggesting that the mites were able to actively reproduce on fish

Evaluating Spirulina as a protein source in Nile Tilapia (Oreochromis niloticus) grow-out diets

Aquaculture growth has intensified the need for a diversification of nutritionally appropriate aquafeed ingredients. The purpose of this study was to evaluate Spirulina, a blue-green microalgae, and soybean meal as the sole protein sources in grow-out Tilapia diets. We constructed 3 experimental diets with soybean meal and 0,15, 30, and 45% Spirulina (SBM, SP15, SP30, and SP45 respectively) as their main protein sources. We compared these diets to a commercial Tilapia diet (CC). Additionally, to evaluate the benefit of fishmeal inclusion, fishmeal was added (2 and 10%) to the most successful Spirulina containing diet (FM2, FM10). We evaluated these experimental diets based on their physical properties, palatability, growth potential, waste production, and overall cost. No significant differences in growth performance were found between any of the diets. Total ammonia nitrogen (TAN) and total phosphorus (TP) levels in each tank were significantly affected by diet (p<0.05). CC had significantly higher TP than the experimental diets and SP15 had significantly higher TAN than the other diets. Only CC was found to be significantly more palatable than the experimental diets, and Spirulina inclusion was inversely correlated to pellet stability. Lastly, SP15 was the most profitable experimental diet. We recommend eliminating fishmeal from grow-out Tilapia diets in favour of soybean meal and Spirulina. Spirulina should, however, be limited to 15% to avoid the negative effects it has on stability and profitability, and its possible effect on feed intake.