Stomachless Fish Research Articles

Effects of dietary indispensable amino acid deficiencies on feed intake in stomachless fish

Evidence suggests that fish are more tolerant than mammals to imbalanced dietary amino acid profiles. However, the behavioral and physiological responses of fish to individual deficiencies in dietary indispensable amino acids (IDAA) remain unclear. This study examined how stomachless fish respond to diets deficient in limiting IDAA (lysine, methionine, and threonine), using Zebrafish (Danio rerio) as a model. The response to deficient diets was assessed based on; 1) growth performance and feeding efficiency; 2) feed intake; 3) expression of appetite-regulating hormones and nutrient-sensing receptors; and 4) muscle postprandial free amino acid (FAA) levels. There were 6 treatments, each with 3 replicate tanks. A semi-purified diet was formulated for each group. The CG diet was based on casein and gelatin, while the FAA50 diet had 50 % of dietary protein supplied with crystalline amino acids. Both were formulated to contain matching, balanced amino acid profiles. The remaining diets were formulated the same as the FAA50 diet, with minor adjustments to create deficiencies in selected IDAA. The (−) Lys, (−) Met, and (−) Thr diets had lysine, methionine, and threonine withheld from the FAA mix, respectively, and the Def diet was deficient in all three. The juvenile Zebrafish were fed to satiation 3 times daily from 21 to 50 days-post-hatch. Results showed that 50 % replacement of dietary protein with crystalline amino acids significantly reduced growth of juvenile Zebrafish. There were no significant differences in growth between the FAA50 group and groups that received deficient diets. The deficiency of singular IDAA did not induce significant changes in feed intake; however, the combined deficiency in the Def diet caused a significant increase in feed intake. This increased feed intake led to decreased feeding efficiency. A significant decrease in feeding efficiency was also observed in the (−) Lys group. There was an observed upregulation of neuropeptide Y (NPY), an orexigenic hormone, in the Def group. Overall, results from this study suggest stomachless fish increase feed intake when challenged with IDAA-deficient diets, and the regulation of NPY might play a role in this response.

Possible transport routes of IgM to the gut of teleost fish

Fish rely on mucosal surfaces as their first defence barrier against pathogens. Maintaining mucosal homeostasis is therefore crucial for their overall well-being, and it is likely that secreted immunoglobulins (sIg) play a pivotal role in sustaining this balance. In mammals, the poly-Ig receptor (pIgR) is an essential component responsible for transporting polymeric Igs across mucosal epithelia. In teleost fish, a counterpart of pIgR has been identified and characterized, exhibiting structural differences and broader mRNA expression patterns compared to mammals. Despite supporting evidence for the binding of Igs to recombinant pIgR proteins, the absence of a joining chain (J-chain) in teleosts challenges the conventional understanding of Ig transport mechanisms.The transport of IgM to the intestine via the hepatobiliary route is observed in vertebrates and has been proposed in a few teleosts. Investigations on the stomachless fish, ballan wrasse, revealed a significant role of the hepatobiliary route and interesting possibilities for alternative IgM transport routes that might include pancreatic tissue. These findings highlight the importance of gaining a thorough understanding of the mechanisms behind Ig transport to the gut in various teleosts. This review aims to gather existing information on pIgR-mediated transport across epithelial cells and immunoglobulin transport pathways to the gut lumen in teleost fish. It provides comparative insights into the hepatobiliary transport of Igs to the gut, emphasizing the current understanding in teleost fish while exploring potential alternative pathways for Ig transport to the gut lumen. Despite significant progress in understanding various aspects, there is still much to uncover, especially concerning the diversity of mechanisms across different teleost species.

Convergent gene losses and pseudogenizations in multiple lineages of stomachless fishes

The regressive evolution of independent lineages often results in convergent phenotypes. Several teleost groups display secondary loss of the stomach, and four gastric genes, atp4a, atp4b, pgc, and pga2 have been co-deleted in agastric (stomachless) fish. Analyses of genotypic convergence among agastric fishes showed that four genes, slc26a9, kcne2, cldn18a, and vsig1, were co-deleted or pseudogenized in most agastric fishes of the four major groups. kcne2 and vsig1 were also deleted or pseudogenized in the agastric monotreme echidna and platypus, respectively. In the stomachs of sticklebacks, these genes are expressed in gastric gland cells or surface epithelial cells. An ohnolog of cldn18 was retained in some agastric teleosts but exhibited an increased non-synonymous substitution when compared with gastric species. These results revealed novel convergent gene losses at multiple loci among the four major groups of agastric fish, as well as a single gene loss in the echidna and platypus.

Synergistic digestibility effect by planktonic natural food and habitat renders high digestion efficiency in agastric aquatic consumers

A digestibility enhancing effect of natural food on stomachless fish model (Cyprinus carpio) was verified by fluorogenic substrate assays of enzymatic activities in experimental pond carp gut flush and planktonic food over a full vegetative season. Then compared with size-matched conspecific grown artificially (tank carp) and an advanced omnivore species possessing true stomach (tilapia, Oreochromis niloticus). Results suggested activities of digestive enzymes (except amylolytic) were significantly higher in pond carp (p ≤ 0.05) than in the size-matched tank carp. Even compared to tilapia, pond carp appeared superior (p < 0.05; proteolytic or chitinolytic activities) or comparable (p > 0.05; phosphatase or cellulolytic activities). Amylolytic, chitinolytic, and phosphatases activities in pond carp gut significantly increased (p ≤ 0.01) over season. Several orders-of-magnitude higher enzymatic activities were detected in planktonic natural food than expressed in carp gut. Amino acid markers in planktonic food revealed a higher share of zooplankton (microcrustaceans), but not phytoplankton, synchronized with higher activities of complex polysaccharide-splitting enzymes (cellulolytic and chitinolytic) in fish gut. Periods of clear water phase low in chlorophyll-a and nutrients, but high in certain zooplankton (preferably cladocerans), may create a synergistic digestibility effect in pond carp. We conclude aquatic ecosystem components (natural food, water, microbiota) enhance fishes' hydrolyzing capabilities of C/N/P macromolecules and even their complex polymers such as cellulose, chitin, and maybe phytate (to be validated), to the extent that being stomachless is not an issue. Aquatic nutritional ecologists may consider that laboratory-based understandings of digestibility may underestimate digestion efficiency of free-ranging fish in ponds or lakes.

Improved innate immunity in juvenile vimba bream (Vimba vimba) fed a dry diet with an additive of hydrochloric acid (HCl)

Abstract A few reports indicate the beneficial effects of organic acids and their salts on anti-infective immunity in fish species. In the role of immunostimulants, inorganic acids may prove to be a much cheaper alternative to their organic equivalents. However, no report has described the effect of using inorganic acid as a feed additive on fish immunity. This study is the first attempt to evaluate the effect of hydrochloric acid (HCl) as a fish feed supplement on cellular immunity in the stomachless fish, cypriniform vimba bream, Vimba vimba (L.). Two groups, three replicates each, of juvenile vimba were fed a commercial dry fish diet or its variant containing a 1.5% additive of HCl for 55 days. The experiment was conducted in a recirculating aquaculture system at 25°C. Mortality, growth, condition factor, feed conversion ratio, respiratory burst activity (RBA), potential killing activity (PKA), and the proliferative response of head kidney lymphocytes were determined for both groups at the end of the experiment and compared. The PKA was higher in the group fed the diet with HCl. For all other parameters studied, there were no significant differences between the experimental groups. The results of the current study prove that the dietary additive of inorganic hydrochloric acid can substantially improve immune response to bacterial infections in juvenile vimba bream.

Tough and Stretchy: Mechanical Properties of the Alimentary Tract in a Fish Without a Stomach.

SynopsisThe mechanical properties of intestinal tissues determine how a thin-walled structure exerts forces on food and absorbs the force of food as it enters and travels down the gut. These properties are critically important in durophagous and stomachless fish, which must resist the potential damage to foreign bodies (e.g., shells fragments) in their diet. We test the hypothesis that the mechanical properties of the alimentary tract will differ along its length. We predict that the proximal region of the gut should be the strongest and most extensible to handle the large influx of prey often associated with stomachless fish that lack a storage depot. We developed a custom inflation technique to measure the passive mechanical properties of the whole intestine of the stomachless shiner perch, Cymatogaster aggregata. We show that mechanical properties differ significantly along the length of the alimentary tract when inflated to structural failure, with 25–46% greater maximal stress, strain, extension ratio, and toughness at the proximal (25%) position. We also find that the alimentary tissues (excluding the heavily muscular rectum) are generally highly extensible and anisotropic, and do not differ in wall circumference or thickness along the alimentary tract. These findings contribute to our knowledge of the mechanical properties of fish intestinal tissues and guide future studies of factors influencing the evolution of fish alimentary systems.

Physical and nutrient stimuli differentially modulate gut motility patterns, gut transit rate, and transcriptome in an agastric fish, the ballan wrasse.

The effects of nutrient and mechanical sensing on gut motility and intestinal metabolism in lower vertebrates remains largely unknown. Here we present the transcriptome response to luminal stimulation by nutrients and an inert bolus on nutrient response pathways and also the response on gut motility in a stomachless fish with a short digestive tract; the ballan wrasse (Labrus berggylta). Using an in vitro model, we differentiate how signals initiated by physical stretch (cellulose and plastic beads) and nutrients (lipid and protein) modulate the gut evacuation rate, motility patterns and the transcriptome. Intestinal stretch generated by inert cellulose initiated a faster evacuation of digesta out of the anterior intestine compared to digestible protein and lipid. Stretch on the intestine upregulated genes associated with increased muscle activity, whereas nutrients stimulated increased expression of several neuropeptides and receptors which are directly involved in gut motility regulation. Although administration of protein and lipid resulted in similar bulbous evacuation times, differences in intestinal motility, transit between the segments and gene expression between the two were observed. Lipid induced increased frequency of ripples and standing contraction in the middle section of the intestine compared to the protein group. We suggest that this difference in motility was modulated by factors [prepronociceptin (pnoca), prodynorphin (pdyn) and neuromedin U (nmu), opioid neurotransmitters and peptides] that are known to inhibit gastrointestinal motility and were upregulated by protein and not lipid. Our findings show that physical pressure in the intestine initiate contractions propelling the bolus distally, directly towards the exit, whereas the stimuli from nutrients modulates the motility to prolong the residence time of digesta in the digestive tract for optimal digestion.

Lysosome-Rich Enterocytes Mediate Protein Absorption in the Vertebrate Gut.

The guts of neonatal mammals and stomachless fish have a limited capacity for luminal protein digestion, which allows oral acquisition of antibodies and antigens. However, how dietary protein is absorbed during critical developmental stages when the gut is still immature is unknown. Here, we show that specialized intestinal cells, which we call lysosome-rich enterocytes (LREs), internalize dietary protein via receptor-mediated and fluid-phase endocytosis for intracellular digestion and trans-cellular transport. In LREs, we identify a conserved endocytic machinery, composed of the scavenger receptor complex Cubilin/Amnionless and Dab2, that is required for protein uptake by LREs and for growth and survival of larval zebrafish. Moreover, impairing LRE function in suckling mice, via conditional deletion of Dab2, leads to stunted growth and severe protein malnutrition reminiscent of kwashiorkor, a devastating human malnutrition syndrome. These findings identify digestive functions and conserved molecular mechanisms in LREs that are crucial for vertebrate growth and survival.

Intestinal Function of the Stomachless Fish, Ballan Wrasse (Labrus bergylta)

Little is known about the digestion of nutrients in stomachless (agastric) fishes with short intestines, such as wrasse. This study describes the digestion, absorption and evacuation rates in ballan wrasse (Labrus bergylta) fed either dry or pre-soaked diets. Ballan wrasse juveniles received either dry or pre-soaked diets containing inert markers to determine intestinal evacuation rates over a 4 to 14 h period after ingestion. The digestive tract evacuation was completed in 12 - 14 h, and was not affected by dietary moisture level. Within the different segments of the intestine, 90 % of the digesta moved from the foregut to the midgut after 4 - 8 h, and over 7 % of the digesta had arrived in the hindgut 4 h after feeding. The foregut was a major site of digestion, where 86 % of carbohydrates, 74 % of proteins, and 50 % of lipids, were absorbed from the diet. The absorption of carbohydrates and lipids increased until the hindgut (98 and 80 %, respectively). Protein absorption continued along the length of the intestine reaching 90 % absorption at the hindgut. Protein and carbohydrate absorption was slightly higher in the foregut for fish fed dry versus moist diets, but this difference disappeared in the midgut. The moisture levels of diet had no effect on the digesta moisture levels, expression of metabolic genes, the levels of nutrients in plasma, or intestinal health. Nine aquaporins were found to be expressed in the wrasse intestinal tissue. Vertebrate aquaporins are involved in water transport from the intestinal lumen into the body and may play a role in maintaining stable moisture level of the digesta in the intestine of ballan wrasse regardless of the initial dietary moisture levels.

Analysis of immunoglobulin and T cell receptor gene expression in ballan wrasse (Labrus bergylta) revealed an extraordinarily high IgM expression in the gut

The serum IgM concentration of ballan wrasse is relatively high, estimated to approximately 13 mg/ml in adult wild fish of 800 g. The present study revealed an unusual high abundance of IgM mRNA in the gut of ballan wrasse. Initially, transcripts encoding IgM, IgT, IgD, TCRα, TCRδ and CD3ε were quantified by RT-qPCR in several tissues of wild caught fish (approx. 800 g), indicating an elevated immune activity in hindgut and an extraordinarily high expression of IgM. Subsequently, a new RT-qPCR analysis was performed on the entire intestine, cut into four different segments, of reared fish (32–100 g). The analysis indicated immune activity along the entire intestine, but not as strong as in the hindgut. Furthermore, similar to the larger fish, the relative abundance of IgM transcripts was higher in the hindgut than in kidney and spleen, although the absolute level of IgM was in general higher in the larger fish. The secreted form of IgM was completely dominant in comparison to the membrane bound form of IgM and the other analysed genes. IgM was purified from gut mucus and external mucosal surfaces by magnetic beads coated with protein A. Mucus IgM reacted with rabbit antisera raised against serum IgM and contained subunits of the same size. Regarding the elevated immune activity in the intestine it is tempting to speculate on a possible compensatory strategy in this lineage of stomach-less fish, and that natural antibodies have an important role in the first line defence.

A study of the digestive enzyme activities in scaleless carp (Gymnocypris przewalskii) on the Qinghai-Tibetan Plateau

Two experiments were conducted to study the digestive enzyme activities in scaleless carp (Gymnocypris przewalskii) on the Qinghai-Tibetan Plateau. In experiment 1, the distribution of digestive enzymes in various digestive organs of G. przewalskii (body weight: 118.24 ± 9.48 g) was studied. Results showed that digestive enzyme specific activities in intestine were significantly higher than those in hepatopancreas (P < 0.05). In intestine, the highest levels of trypsin and chymotrypsin specific activities were found in foregut and hindgut, the highest levels of lipase and amylase specific activities were observed in foregut (P < 0.05). In experiment 2, temporal changes of the digestive enzyme specific activities after feeding were investigated in G. przewalskii (body weight: 305.32 ± 28.78 g). Results showed that lipase and amylase specific activities in foregut approached maximum levels at 2 h after feeding and then decreased to the basic level at 6 h after feeding. The trypsin specific activities in foregut and hindgut reached the maximum levels at 2 h after feeding and then to the basic level at 8 h after feeding. In conclusion, as stomach-less fish, foregut of G. przewalskii contributed more to the nutrients digestion. The fish could digest nutrients (protein, fat and carbohydrate) efficiently. Thus, increasing in the amount of G. przewalskii resources could be achieved by improving nutritional state in artificial culture systems.

Evaluation of nano-ZnOs as a novel Zn source for marine fish: importance of digestive physiology

Waterborne nanotoxicology of zinc oxide nanoparticles (nano-ZnOs) has been extensively studied over the past decade, whereas their potential dietary toxicity and applications were seldom investigated. In the present study, we systematically investigated both short-term bioavailability and chronic effects of nano-ZnOs to two marine fish (marine medaka Oryzias melastigma and red drum Sciaenops ocellatus). At normal supplementary level (80 mg Zn/kg), red drum (with a stomach) had similar assimilation efficiencies of nano-ZnOs and ZnCl2. Correspondingly, in vitro digestion experiments showed the continuous dissolution of nano-ZnOs in acid environment. In contrast, nano-ZnOs were more bioavailable than ZnCl2 to medaka (stomach-less) at 80 mg Zn/kg supplementary level. There results were further validated by using bulk-ZnOs. Chronic dietary exposure to nano-ZnOs (80 mg/kg) significantly enhanced the antioxidative defenses in medaka, with no negative effect on fish growth. Beneficial effects disappeared in the high dietary nano-ZnOs (300 mg/kg) treatment. For the first time, we provided direct evidence that nano-ZnOs was more bioavailable than ZnCl2 and bulk-ZnOs to stomach-less fish at normal dietary Zn inclusion level (<80 mg/kg), with potential benefits on antioxidative defenses. It is also necessary to pay attention to the dietary nano-ZnOs toxicity on stomach-less fish due to the presence of real ‘nano-effects.’

Histology of the digestive system of the garfish Belone belone (Teleostei: Belonidae)

Five garfish Belone belone (Linnaeus, 1761) were sampled to study the morphology of the digestive system. Hematoxylin-eosin staining as well as Alcian blue/PAS (Periodic Acid Schiff) were used in order to elucidate the histological features of the digestive organs in garfish. Garfish B. belone is a stomachless fish whose digestive system is a hollow tube made of oesophagus and intestines. The oesophagus consists of three distinctive layers: the mucosa, the muscular layer and the outer layer. The oesophageal epithelium contains abundant goblet cells. All three observed parts (anterior, middle and posterior) of the intestines consisted of four-layered wall containing muscosa, submucosa, muscular layer and outer layer. The liver as an associated digestive gland also contains some pancreatic tissue spread out through the liver parenchyma. The results show that the histology of the digestive system in garfish is congruent with its feeding habits.

Digestive Physiological Characteristics of the Gobiidae: - Characteristics of CCK-producing Cells and Mucus-secreting Goblet Cells of Stomach Fish and Stomachless Fish.

In this study, we investigated the characteristics of CCK-producing cells and mucus-secreting goblet cells with respect to stomach fish and stomachless fish of the Gobiidae in order to provide a basis for understanding the digestive physiology. Hairychin goby (Sagamia geneionema), which is stomachless fish, the numbers of mucus-secreting goblet cells is highest in the posterior intestine portion (P<0.05), while CCK-producing cells are scattered throughout the intestine. Gluttonous goby (Chasmichthys gulosus), which is stomach fish, mucus-secreting goblet cells are most abundant in the mid intestine portion (P<0.05), whereas CCK-producing cells are observed only in the anterior and mid intestine portion. Trident goby (Tridentiger obscurus) which is stomach fish, mucus-secreting goblet cells were most abundant in the mid intestine portion (P<0.05). CCK-producing cells are found in the anterior and mid intestine portion. Giurine goby, Rhinogobius giurinus which is also stomach fish, the largest number of mucus-secreting goblet cells showed in anterior intestine portion except for esophagus (P<0.05). CCK-producing cells are present only in the anterior and mid intestine portion. In S. geneionema, digestive action occurs in the posterior intestine portion to protect and functions to activate digestion. In contrast, in C. gulosus, T. obscurus and R. giurinus, their digestive action occurs in the anterior and mid intestine portion to protect and functions to activate digestion. Further studies of the modes of food ingestion by these fish, the contents of their digestive tracts, and the staining characteristics of the goblet cells need to be carried out.

Histological, histochemical and ultrastructural analysis reveals functional division of the oesophagogastric segment in freshwater tubenose goby Proterorhinus semilunaris Heckel, 1837

Histological and histochemical features of the oesophagogastric segment of the alimentary canal as well as ultrastructure of gastric gland cells of freshwater tubenose goby Proterorhinus semilunaris were examined. The studies revealed that despite the lack of anatomical distinction, the oesophagogastric segment is histologically divided into the oesophagus, oesogaster and stomach, which provides evidence for the functional compartmentation of this organ. The oesophagus was characterised by the presence of numerous goblet cells secreting mainly a mixture of neutral and acid mucopolysaccharides. In the stomach, the apical zone of the surface epithelial cells contained neutral mucopolysaccharides. Numerous proliferating cells were scattered throughout the surface epithelium. In the lamina propria of the stomach, a well-developed layer of gastric glands was observed. The glands were of the alveolar type and occupied nearly the entire length of the stomach except the pyloric region. The gastric gland cells were varied into light and dark; however, their ultrastructure was identical. All cells had numerous mitochondria and a well-developed tubulovesicular system typical for the oxynticopeptic cells, but pepsinogen granules were not present in the cytoplasm of these cells. These findings contribute new evidence to literature reports that not all gobiid fish are stomachless. Moreover, they suggest higher adaptation of the species to utilise protein-rich food compared to stomachless fish, and its ability to adjust the alimentary canal quickly to changing diet. How this may facilitate establishment of P. semilunaris in invaded environments remains an open question.

Effect of ingestion on the stable isotope signatures of marine herbivorous fish diets

Stable isotope analysis is widely used to investigate the diet–consumer relationships of free-ranging animals, including fishes. However, measuring the isotope signature of relevant diet items can be problematic when little is known about consumer diet choice, or when individual diet items are difficult to collect in the field. Here we tested the viability of using ingested material as a proxy for fresh diet items in a field study by examining the effect of ingestion on the δ15N and δ13C values of diet items commonly consumed by the marine herbivorous fish Odax pullus (Labridae). Ingestion had a significant effect on the δ15N or δ13C value of three of the five diet items considered. Two diet items showed a clear and consistent change in isotopic signature following ingestion, indicating that discrimination between light and heavy isotopes occurs during the early stages of processing in this stomachless fish. The potential for isotope signatures to change following ingestion suggests that caution should be taken when using ingested material as a proxy for diet items in studies of marine herbivory. Additionally, the predictable effect of ingestion demonstrates the potential for digestion to make a large contribution to the fractionation observed in trophic studies of marine herbivory.

Pemberian Pakan dengan Kadar Serat Kasar yang Berbeda Terhadap Daya Cerna Pakan pada Ikan Berlambung dan Ikan Tidak Berlambung &lt;br&gt;&lt;i&gt;[Feeding With Different Levels Of Crude Fiber On The Diggestibility Of Feed In True Stomach Fish and Stomachless Fish ]&lt;i&gt;

Abstract Feed plays an important role in fish farming activities. Meeting the needs of feed quality and quantity sufficient aims to increase farming production, in addition to the feed given to fish properly assessed not only from the composition of the feed but also of how much the components contained in the feed can be absorbed and utilized by the fish in his life. Factors that may affect the digestibility of feed include feed composition, range and quality of the enzyme in the intestine or the stomach of fish (NRC, 1993) while Mudjiman (2002) states that the specific differences in the digestive system in fish can lead to differences in the ability of fish to digest feed, for it is used in this study true stomach fish and stomachless fish. This study aims to determine whether there are differences in the digestibility of crude fiber and determine the optimum content in true stomach fish and stomachless fish. The study design used in this study was Complete Randomized Design (CRD) factorial pattern with two factors, factor A is a type of fish and factor B is the type of feed. Analysis of the data were processed using Analysis of Variance (ANOVA) to determine whether there is an interaction effect between the treatment given. If there is a difference in the effect of test distance followed by Multiple Duncan (Duncan's Multiple Range Test). Based on the research results showed that there is a very real difference (p&lt;0.01) on the digestibility of fish and feed efficiency in true stomach fish and stomachless fish. The highest digestibility resulting in treatment A2 (81,26%) while for fish feed efficiency, the true stomach fish has a higher feed efficiency than the stomachless fish is 20,91%.

Enzymatic digestion in stomachless fishes: how a simple gut accommodates both herbivory and carnivory

The lack of a stomach is not uncommon amongst teleost fishes, yet our understanding of this reductive specialisation is lacking. The absence of a stomach does not restrict trophic preference, resulting in fishes with very similar alimentary morphology capable of digesting differing diets. We examined the digestive biochemistry of four beloniform fishes: two herbivorous halfbeaks (Hemiramphidae) and two carnivorous needlefish (Belonidae) to determine how these fishes digest their respective diets with their simple, short gut. We found that although the halfbeaks showed significantly greater α-amylase activity than that of the needlefish (P<0.01), trypsin, lipase, aminopeptidase and maltase activity were not substantially different between the two families. We also found that habitat (freshwater vs. marine) appears to play a significant role in digestive capability, as the two freshwater taxa and the two marine taxa were significantly different (ANOSIM; dietary Gobal R=0.544, P=0.001, habitat Global R=0.437, P=0.001), despite their phyletic and dietary similarities. Our findings offer partial support for the adaptive modulation hypothesis, support the Plug-Flow Reactor model of digestion in herbivorous halfbeaks and also support the compartmental model of digestion but suggest that another model is required to describe stomachless carnivorous needlefish.

Effects of protein-, peptide- and free amino acid-based diets in fish nutrition

In the present review, we summarize data related to the utilization of purified diets formulated with the purpose of determining the amino acid requirements in fish independent of the ontogenetic stage and the morphological characteristics of the digestive tract. Expanding present knowledge on the formulation of protein, free amino acid (FAA) and synthetic dipeptide-based diets can provide possible insights that might lead to a better understanding of the mechanism of amino acid utilization in the growth of fish. Differences exist in the utilization of protein, dipeptides or free amino acids for growth between stomach-possessing and stomachless fish with respect to their response to manipulating the proportion of protein and dipeptides in the formulas. Free amino acid-based diets are uniformly inferior. The effects of diet manipulation on indispensable FAA concentrations in the body (muscle) are not simply the result of deamination or the protein synthesis/degradation ratio. The hydroxyproline/proline ratio was confirmed to be of value in quantifying muscle collagen degradation/synthesis and can perhaps be used to quantify the amino acid requirement necessary to maximize the utilization (deposition) of dietary amino acids. In summary, indispensable amino acid requirements for maximum growth in fish can be addressed using diets formulated from protein/peptide/FAA sources.

Assessment of enzymatic efficiency on protein digestion in the tilapia Oreochromis niloticus

The present study develops an experimental procedure aimed to estimate the efficiency of protein digestion in fish by measuring both gut transit rate and total amount of the main intestinal proteases (trypsin and chymotrypsin). The selected species was the Nile tilapia (Oreochromis niloticus). Total time for digestion, calculated through the estimation of gut transit rate using differently colored feeds, was 7.15h. Mean production of trypsin and chymotrypsin was 15.94 and 24.11mU in the proximal intestine and much lower (2,39, 4.90mU) in the distal intestine. The enzyme efficiency, calculated from the average enzyme activity and time of residence of the digesta in each intestinal section, points to the major role of proximal intestine in protein digestion for this species. Results are discussed in relation to the main features characterizing digestion in stomachless fish.