Resumo O objetivo deste trabalho foi avaliar a digestibilidade da proteína, dos aminoácidos e da energia bruta de hidrolisado de fígado e carne suínos pela tilápia-do-nilo (Oreochromis niloticus). Os peixes foram distribuídos em 12 tanques com fundo cônico, em delineamento inteiramente causalizado, tendo sido alimentados com as seguintes três dietas, com quatro repetições cada uma: dieta referência com farinha de soja e de peixe; e duas dietas teste, uma com hidrolisado de fígado suíno e outra com hidrolisado de carne suína. Os coeficientes de digestibilidade aparente foram elevados para ambos os hidrolisados, tendo sido acima de 83% para matéria seca, 95% para proteína bruta e 92% para energia. Em relação aos aminoácidos, os coeficientes permaneceram entre 98–100% para os dois hidrolisados. Os percentuais de digestibilidade dos hidrolisados foram maiores do que os dos ingredientes proteicos, tanto de origem vegetal como animal, comumente utilizados na fabricação de dietas para esta espécie de peixe. Os hidrolisados testados têm potencial para serem usados na formulação de dietas para tilápia-do-nilo.

Abstract The objective of this work was to evaluate the digestibility of the protein, amino acids, and gross energy of swine liver and meat hydrolysates by Nile tilapia (Oreochromis niloticus). The fish were distributed into 12 tanks with conical bottoms, in a completely randomized design, and fed with the three following diets, with four replicates each: a reference diet with soybean and fish meal; and two test diets, one with swine liver hydrolysate and the other with swine meat hydrolysate. The coefficients of apparent digestibility were high for both hydrolysates, being above 83% for dry matter, 95% for crude protein, and 92% for gross energy. Regarding amino acids, the coefficients remained at 98–100% for the two hydrolysates. The digestibility percentages of the hydrolysates were higher than those of the protein ingredients, both of plant and animal origin, commonly used in the formulation of diets for this fish species. The tested hydrolysates have potential to be used in the formulation of diets for Nile tilapia.

ABSTRACT This study aimed at evaluating diets containing protein hydrolysate from poultry byproducts and swine liver (PHPPL), at different inclusion levels, for Nile tilapia (Oreochromis niloticus) juveniles. Seven diets were evaluated, being a negative control (free of both hydrolysate and fishmeal) and positive control (free of hydrolysate but containing fishmeal), besides five diets with 1, 2, 3, 4, or 5% inclusion of the mixed protein hydrolysate. Significant effects were observed regarding the animals' final length, with higher values with the 1% inclusion level than the negative control. The liver's quantitative evaluation revealed that inclusions above 3% might lead to severe alterations in the organ's morphology. The use of PHPPL in the diets that did not contain fishmeal has shown to be effective in maintaining the performance parameters of Nile tilapia. Thus, its use is recommended considering an inclusion level of 3%.

ABSTRACT This study determined the compelling palatability of Atractus Aqva® flavoring for Nile tilapia juveniles (Oreochromis niloticus). Five isoproteic (40% crude protein) and isoenergetic (3,420 kcal kg-1) experimental diets were elaborated containing 0.25 (A25), 0.50 (A50) and 0.75% (A75) flavoring inclusion, a positive control diet with 10% fishmeal (FPE) and a negative control without fishmeal (SPE). Five juvenile individuals (2.58 ± 0.27 g) were distributed in five 10 L tanks and were fed four times a day with one of the diets, randomly raffled. The same number of pellets was offered, and the following behaviors were observed: time to capture the first pellet, number of pellet rejections, and number of approximations without capture and consumed pellets in each feeding event, using three-minute recordings with a digital camera. A significant effect (P < 0.05) was found regarding the number of approximations without capturing the pellet, as well as a higher palatability index for A75, followed by A50, A25, SPE and FPE. Therefore, it was concluded that A75 provided the highest compelling palatability of all diets by increasing the palatability index by 10.49% and displaying a 23.13% reduced rejection of pellets, besides presenting a 3.3 fold reduction in the number of approximations without capturing pellets with diet FPE.

ABSTRACT This research was conducted to determine optimal dietary histidine requirement of grow-out Nile tilapia, Oreochromis niloticus, based on muscle development, expression of muscle-growth-related genes, and blood parameters. Fish (n = 288, initial body weight of 64.17±0.53 g) were fed extruded diets with graded levels of histidine (4.23, 5.44, 7.17, 8.91, and 11.57 g kg−1), containing approximately 289 g kg−1 crude protein and 3565 kcal kg−1 digestible energy. The study followed a completely randomized design with five treatments and four replicates each, for 65 days. There was a quadratic effect of dietary histidine on final body weight, feed conversion, and net protein utilization, and the best values were optimized at 8.09, 7.88, and 7.33 g kg−1, respectively. Feed intake, hepatosomatic index, survival, body composition, and blood parameters of total protein, glucose, triglycerides, cholesterol, hematocrit, and hemoglobin were not affected by dietary treatments. Predominance of hypertrophic growth and higher mRNA levels of myogenin and MyoD were observed in fish fed histidine from 5.44 to 11.57 g kg−1 compared with fish fed histidine at 4.23 g kg−1. The mRNA expression of myostatin was not affected by dietary treatments. The dietary requirement of histidine for grow-out Nile tilapia was determined at 8.09 g kg−1, considering growth performance, muscle development, and gene expression responses.

ABSTRACT This study aimed at determining the compelling palatability of different protein hydrolysates for Nile tilapia juveniles (Oreochromis niloticus). Four isoproteic (30% crude protein) and isoenergetic (3,200 kcal kg−1) experimental diets were formulated, with a 5% inclusion level of poultry hydrolysate protein (PHF), or swine liver hydrolysate protein (PHS), or feather hydrolysate protein (PHP) and a control treatment containing 5% of fishmeal (FPE). Four juveniles (2.9 ± 0.01 g) were distributed in 10 L tanks and fed four times a day, and before each feeding event, diets were drawn. The same amount of pellets from each diet was offered, and feeding behaviors were recorded during three minutes for each feeding event, referred to the time of capture of the first pellet, number of pellet rejections, and number of approximations without capturing pellets and quantity of consumed pellets. A significant effect (P < 0.05) was observed regarding a higher consumption of pellets and palatability index for PHF, followed by PHS, FPE, and PHP. Therefore, it was concluded that PHF provided the highest compelling palatability for Nile tilapia juveniles, by displaying a 10.82% increase of the palatability index, 17% of final feed consumption, and presented a rejection number 6.89 times lower than FPE.

RESUMO: O presente trabalho tem como objetivo investigar a estabilidade de pellets e a lixiviação do fósforo na água proveniente de diferentes dietas formuladas para juvenis de tilápia do Nilo (Oreochromis niloticus), considerando distintas fontes de fósforo e diferentes tempos de exposição na água. Para tanto, foram elaboradas seis dietas com variação da fonte de fósforo (1: fosfato dicálcico (DP); 2: farelo de carne e ossos (MBM); 3: farelo de aves (PM); 4: farelo de anchova (AM); 5: farelo industrial de filetagem de tilápia (TM); 6: farelo de osso calcinado (CBM)), as quais foram submetidas a quatro tempos de exposição em água (5, 10, 15 e 20 minutos), com três repetições. Utilizaram-se 72 aquários de 30 litros, sendo cada um deles uma unidade experimental. A água dentro dos aquários foi mantida sob constante aeração e temperatura ao redor de 25 °C. Todas as dietas foram avaliadas quanto à condutividade elétrica da água, turgidez, lixiviação de matéria mineral, flotação de pellets e lixiviação total do fósforo. Apenas a turgidez e a flutuação dos pellets variaram com as diferentes fontes de fósforo nas dietas. A dieta MBM apresentou a maior turgidez de pellets. As dietas PM, AM e CBM apresentaram a maior flutuação de pellets. A lixiviação do fósforo total teve um efeito linear com o aumento do tempo de exposição, resultando em maior liberação de fósforo na água. A lixiviação de matéria mineral apresentou interação entre fontes de fósforo e tempos de exposição das dietas, com efeito linear para a dieta TM. As dietas PM, AM e CBM apresentam as menores concentrações de efluentes em relação a dieta TM. Esses resultados revelaram que dietas formuladas com diferentes fontes de fósforo apresentam ações distintas na água em relação ao potencial poluidor.

ABSTRACT: The present research aimed to investigate the stabil¬¬ity of pellets and phosphorus leaching of diets formulated for juveniles of Nile tilapia (Oreochromis niloticus), with different sources of phosphorus and different exposure times in water. Six diets were elaborated by varying the source of phosphorus (1 ‒ dicalcium phosphate (DP); 2 ‒ meat and bone meal (MBM); 3 ‒ poultry meal (PM); 4 ‒ anchovy meal (AM); 5 ‒ tilapia filleting industrial meal (TM); 6 ‒ calcined bone meal (CBM)) and, then, were submitted to four exposure times in water (5, 10, 15 and 20 minutes), with three replicates. Thus, 72 aquariums of 30‒liters were used, each being an experimental unit. All diets were evaluated for electrical conductivity of water, turgidity of pellets, mineral matter leaching, flotation of pellets, and total phosphorus leaching. Only turgidity and flotation of pellets varied with the different sources of phosphorus in the diets. The MBM diet had the highest turgidity of pellets. The PM, AM, and CBM diets had the highest flotation of pellets. The total phosphorus leaching had a linear effect with the increase of the exposure time, showing a greater release of phosphorus in the water with increase of exposure time. Data showed that PM, AM, and CBM diets had less potential impact on the aquatic environment. Conversely, the TM diet has greater polluting potential. These results showed that diets formulated with different sources of phosphorus exhibit distinct actions in the water, providing different effects on the fish culture environment.

RESUMO Neste estudo foi verificada a influência da valina no desempenho zootécnico, composição centesimal e crescimento das fibras musculares esqueléticas de alevinos de tilápia do Nilo. Foram utilizados 270 peixes (peso médio inicial de 1,57 ± 0,05 g e comprimento total inicial de 4,16 ± 0,46 cm), distribuídos em 18 caixas (250 litros), em delineamento inteiramente ao acaso com seis tratamentos e três repetições. Foram formuladas seis dietas (26,81% PD e 3200,00 kcal ED), com níveis crescentes de valina (0,82; 0,86; 0,98; 1,04; 1,10 e 1,26% da dieta). Foram avaliados o desempenho zootécnico, composição centesimal dos peixes e a distribuição das fibras musculares. Não houve efeito dos diferentes níveis de valina (P>0,05) para o desempenho zootécnico, composição centesimal e frequência de distribuição das fibras musculares. Recomenda-se a inclusão de 0,82% de valina na dieta (2,65% de valina da proteína bruta) para alevinos de tilápia do Nilo.

ABSTRACT This study verified the effect of valine on the zootechnical performance, percentage composition and growth of skeletal muscle fibre in fingerlings of Nile tilapia. A total of 270 fish (average initial weight 1.57 ± 0.05 g and total initial length 4.16 ± 0.46 cm) were used, distributed in 18 tanks (250 litres), in a completely randomised design with six treatments and three replications. Six diets (26.81% DP and 3200.00 kcal DE) were formulated with increasing levels of valine (0.82, 0.86, 0.98, 1.04, 1.10 and 1.26% of the diet). The zootechnical performance, percentage composition of the fish, and muscle-fibre distribution were evaluated. There was no effect from the different levels of valine (P>0.05) on zootechnical performance, percentage composition or the frequency distribution of muscle fibre. The addition of 0.82% valine (2.65% crude protein valine) is recommended in the diet of Nile tilapia fingerlings.

ABSTRACT The objective of this study was to assess the L-lysine effect in silver catfish, Rhamdia voulezi female reproduction. Four hundred fish were used distributed in a random in 16 net cages (25 fish each x 4 replicates = 100 fish per treatment). The treatments consisted in four diets, isoproteic and isoenergetic (30% crude protein and 3,500 kcal kg-1 digestible energy) with different L-lysine levels: T1: 1.30; T2: 1.40; T3: 1.60 and T4: 1.95%. After 185 days of experiment 18 females per treatment were weighed, measured, and submitted to hormonal induction (0.5 and 5.0 mg kg-1 Carp Pituitary Extract). The females were then sacrificed and had their ovaries, liver and fat removed and the respective organosomatic indices were estimated. With regard to the reproductive parameters, the released oocytes, absolute fecundity and remaining ovaries were influenced (P < 0.05) by the diet, and the highest mean values were observed in the treatment with 1.95% L-lysine. Among the organosomatic indices, only the visceral fat was influenced (P < 0.05). The estradiol levels and the composition of essential amino acid in oocytes were not affected (P > 0.05). We can conclude that L-lysine affects the reproductive parameters and accumulation of visceral fat in R. voulezi.

RESUMO. Objetivou-se avaliar a digestibilidade do hidrolisado proteico seco do resíduo da filetagem de tilápias (HPST) e sua inclusão em dietas para larvas de tilápia do Nilo. Para determinar os coeficientes de digestibilidade aparente, duas dietas foram elaboradas, referência e teste (com 20% do HPST) e para avaliação da inclusão, seis dietas foram formuladas com 0,0, 2,0; 4,0; 6,0, e 8,0% de HPST. Os coeficientes de digestibilidade aparente da proteína e energia bruta foram de 89,5 e 98,3%, respectivamente. Nos níveis acima de 4,0% de inclusão de HPST o peso e comprimento final e ganho em peso foram prejudicados, no entanto a sobrevivência foi maior (p < 0,05). O HPST pode ser utilizado em dietas para tilápias em função dos elevados coeficientes de digestibilidade para proteína bruta e energia bruta. A inclusão de até 4,0% de HPST não afeta o desempenho produtivo e a sobrevivência de larvas de tilápias do Nilo.

ABSTRACT. This study aimed to evaluate the digestibility of tilapia by-product protein hydrolysate powder (TBHP) from tilapia filleting by-product, and its inclusion in diets for Nile tilapia larvae. In order to determine the apparent digestibility coefficients, two diets were formulated, the reference diet and the test diet (20% of TBHP) and, to evaluate the inclusion, six diets were formulated, which were with 0.0, 2.0; 4.0; 6.0, and 8.0% of TBHP. The apparent digestibility coefficients of crude protein and gross energy were 89.5 and 98.3%, respectively. At levels above 4.0% of inclusion of TBHP, the weight, final length and weight gain were impaired, however, survival rate was higher (p < 0.05). The TBHP can be used in diets for tilapia due to the high digestibility coefficients for crude protein and gross energy. The inclusion of up to 4.0% of TBHP does not affect the reproductive performance and survival rate of Nile tilapia larvae.

Abstract The objective of this work was to produce protein hydrolysates from by-products of the Nile tilapia fileting process, and to assess the effects of different hydrolysis times on the antioxidant activity of the hydrolysed animal-based protein, in free form and incorporated into a food matrix. Gutted tilapia heads and carcasses were hydrolysed by Alcalase® for different hydrolysis times producing six hydrolysates. The protein content, degree of hydrolysis, reverse-phase high-performance liquid chromatography, and antioxidant activity by the ORAC, FRAP and TEAC methods were analysed. Three mini-hamburger formulations were produced and the lipidic oxidation of mini-hamburger was determined by TBARS. The protein contained in the residue was completely recovered in the process. The hydrolysates varied in their degree of hydrolysis, but presented similar levels of antioxidant activity. In the mini-hamburgers the hydrolysate was capable of delaying oxidation after 7 days of storage. Hydrolysis of tilapia processing by-products produced peptides may be used in the formulation of functional foods.

Resumo O objetivo deste trabalho foi avaliar o efeito do peso de abate e do sexo sobre os rendimentos do processamento e sobre a composição centesimal do jundiá (R. voulezi). Foram calculados os rendimentos percentuais em relação à massa do peixe inteiro (rendimentos da carcaça, tronco limpo, músculo abdominal, filé, partes comestíveis, cabeça, pele, gônadas e gordura visceral). Não houve diferença estatística nos rendimentos entre as classes (P>0,05). Entretanto, ao se avaliarem os rendimentos entre os sexos, foi observada diferença significativa (P<0,05) para os rendimentos da carcaça, tronco limpo, músculo abdominal e gordura visceral, sendo que os machos obtiveram os maiores valores nestes itens. As fêmeas apresentaram maior (P<0,05) rendimento das gônadas. Os teores de proteína bruta, cinzas e carboidratos não diferiram (P>0,05) entre as classes, porém, a umidade, lipídeos e valor calórico tiveram diferença significativa (P<0,05) entre as classes, sendo que a umidade diminuiu com o aumento do tamanho dos peixes e o teor de lipídeos e valor calórico foi maior nos peixes da classe 301-400 g. Concluiu-se que os rendimentos do processamento do jundiá (R. voulezi) com massa entre 100 e 400 g são iguais, sendo que os peixes de 301 a 400 g apresentam maior teor de lipídeos no filé.

Abstract The aim of this study was evaluate the effect of slaughter weight and sex on processing yield and on the proximate composition of Rhamdia voulezi. We calculated the percentage yield of the whole fish (carcass, clean trunk, abdominal muscle, fillet, edible parts, head, skin, gonads and visceral fat yield). There was no statistical difference in yields among weight classes (P>0.05). However, when assessing the income between sexes we observed significant difference (P<0.05) for carcass, clean trunk, muscle and abdominal visceral fat yield, and males presented the highest values for these items. Females had higher (P<0.05) gonads yield. Crude protein, ashes and carbohydrates did not differ (P>0.05) among the classes, however, moisture, lipids and calories had significant difference (P<0.05) among the classes, and humidity decreased with increasing size of the fish, and lipid content and calorific value were higher for fish weighing 301-400 g. We concluded R. voulezi with mass between 100 and 400 g presents equal yield processing, and fish weighing 301-400 g have higher lipid content in the fillet.

O estudo objetivou avaliar a produção de perifíton em susbtratos artificiais, considerando-o como fonte de alimento vivo de baixo custo para peixes. Foram submergidos substratos artificiais como madeira, plástico preto, acrílico, fibra de vidro, cerâmica e vidro (24 lâminas de cada substrato com 144cm²), 20cm abaixo da coluna de água por um período de 35 dias no inverno e no verão. As lâminas foram instaladas em um viveiro de 20m³, em delineamento inteiramente casualizado, e foi avaliada a produção de biomassa em diferentes fases durante o inverno e o verão. Foram coletadas semanalmente quatro laminas de cada substrato e a comunidade perifítica foi cuidadosamente raspada com espátula e fixada em formaldeído a 4,0%. Foi avaliada a produtividade em biomassa por área e por dia dos substratos artificiais. Os resultados evidenciaram característica periodicidade na produção de biomassa perifítica e uma significante variabilidade nos períodos e nas estações de coleta nos diferentes substratos artificiais utilizados. Cerâmica e madeira apresentaram os melhores resultados no verão, enquanto a madeira apresentou melhores resultados no inverno. A produção de biomassa perifítica difere entre períodos, substratos e estações. Madeira e cerâmica podem ser indicados para a produção de biomassa perifítica tanto no inverno quanto no verão.

This study evaluated the periphyton production on artificial substrates considering it as a source of low cost live food for fish. Blades of artificial substrates such as wood, black plastic, acrylic, fiberglass, ceramics and glass (all with 144cm2 blades, 24 for each substrate) were submerged 20.0cm below the water column for 35 days in the winter and 42 days in the summer. The blades were randomly installed in 200m3 pond and evaluated for the biomass production at different phases during the summer and winter. Four blades of each substrate were collected weekly, and the periphytic community was carefully scraped with a spatula and fixed in 4% formaldehyde. The periphytic biomass productivity was evaluated by artificial substrate area and per day. The results evidenced the characteristic periodicity in periphyton biomass production and a significant variability in the collect period and season in the different artificial substrates used. Ceramic and wood showed the best results in the summer while wood showed the best results in the winter. The priphyton biomass productions differ among periods, substrates and seasons. Wood and ceramics could be indicated for periphyton biomass production in either winter or summer.

The objective of this study was to evaluate the incorporation of conjugated linoleic acid and α-linolenic acid in fillets of pacu fish raised in net cages and fed diets enriched with these acids. The fish were fed for 49 days, and at the end of this period the fatty acid content in the fillets was determined by gas chromatography. Concentrations of α-linolenic acid, eicosapentaenoic acid, and the total omega-3 (n-3) fatty acid in the fillets increased, improving the n-6/n-3 ratio. In addition, the incorporation of conjugated linoleic acid in the fish fillets proved well established. This study showed that the use of diets enriched with conjugated linoleic acid and α-linolenic acid results in the incorporation of these acids in the of pacu fish fillets, improving their nutritional quality.

The objective of this study was to investigate the fatty acid composition of Pimedolus maculatus fillets of fish fed with different diets. The fish were submitted to an adaptation period (over 30 days) and fed only a control diet (diet I). After this period, the fish were divided into two groups: one group received a diet enriched with flaxseed oil (diet II), and the other received a diet enriched with conjugated linoleic acid (CLA) (diet III). Subsequent collections were undertaken after 25 and 50 days. Compared to the control samples, fish fed diet II showed an increase in concentrations of total fatty acid omega-3 (n-3) in the fillets, with an improvement ratio of n-6/n-3. The incorporation of CLA into fish fed diet III was successful. Supplementing the diet of Pimedolus maculatus with CLA and flaxseed oil led to improvements in nutritional quality and fatty acid profile of the fish fillets.

El objetivo de este estudio fue el de evaluar el efecto de la inclusion de aditivos en el agua durante el transporte de pacu (Piaractus mesopotamicus) en estado juvenil sobre la sobrevivencia de los peces una vez transferidos y mantenidos en jaulas de cultivo. Ochocientos peces de 30 ± 1,75 g/ pez fueron mantenidos en ayuna por 24 h y luego distribuidos al azar en 20 bolsas de plástico de 30 l (40 peces por bolsa). Cada bolsa fue dispuesta en un recipiente plástico. Los peces fueron transportados por 2 h. Los aditivos y concentraciones usadas en el presente estudio fueron: sal (8 g/l), florfenicol (0,01 g/l), oxitetraciclina (0,001 g/l), y una combinación de sal (8 g/l) + yeso (1 g/l). Un tratamiento control (no aditivos) fue incluido en el estudio. Parámetros de calidad del agua tales como el oxígeno disuelto, la saturación de oxígeno, pH, temperatura, nitrito y amoniaco fueron medidos al principio y al final del periodo de tranporte. El uso de aditivos en el agua durante el transporte del pacu no mostró un efecto sigificativo (P>0,05) sobre la mortalidad de los peces mantenidos en jaulas de cultivo. Los resultados del presente estudio destacan la ineficiencia de la adición de estos compuestos en el agua durante el transporte del pacu.

The aim of this study was to assess the effect of the inclusion of additives into the water during transportation of juvenile pacu (Piaractus mesopotamicus) on the survival rate of fi sh once they are transferred and stocked in cages. Eight hundred fi sh of approximately 30 ± 1.75 g/fi sh of body weight were fasted for 24 h and then distributed into 20 plastic bags of 30 l (40 fi sh per bag). Each bag was then placed in a plastic container. The transportation period lasted for 2 h. The additives and concentrations used in the present study were: salt (8 g/l), fl orfenicol (0.01 g/l), oxytetracycline (0.001 g/l) and a combination of salt (8 g/l) + gesso (1 g/l). A control treatment (with no addition of additives) was included in the study. Water quality parameters such as dissolved oxygen, oxygen saturation, pH, temperature, nitrite and ammonia were measured at the beginning and at the end of the transportation process. The use of additives in the water during transportation of pacu did not have a signifi cant (P>0.05) effect on the mortality of fish once they were stocked in cages. The results from the present study highlight the ineffi ciency of the addition of these compounds in the water during transportation of pacu.

O objetivo deste estudo foi avaliar a eficiência de uma prática de manejo utilizada e recomendada aos produtores de peixe, trata-se do uso de aditivos na água de transporte de juvenis de pacu (Piaractus mesopotamicus) sobre a sobrevivência pós transporte dos peixes posteriormente estocados em tanques-rede. Foram distribuídos inteiramente ao acaso 800 peixes com aproximadamente 30 ± 1,75 g, em 20 embalagens plásticas de 30 l contendo 40 peixes/embalagem. Os tratamentos foram compostos pelos seguintes aditivos na água de transporte: sal (8 g/l), florfenicol (0,01 g/l), oxitetraciclina (0,001 g/l), associação de sal (8 g/l) + gesso (1 g/l) e um tratamento controle sem adição de aditivos. Após 24h de jejum, os peixes foram despescados e transferidos para embalagens plásticas e transportados durante 2 horas. Mediram-se os parâmetros de qualidade de água como: oxigênio dissolvido, saturação de oxigênio, pH, temperatura, nitrito e amônia no início e ao fi nal do transporte. Verifi couse o uso de aditivos na água de transporte não infl uencia (P>0,05) na diminuição da mortalidade dos animais, ressaltando a inefi ciência do uso destes compostos nesta prática de manejo em pisciculturas.