Assessment of Compensatory Growth in Channel Catfish Ictalurus punctatus R. and Associated Changes in Body Condition indices

A feeding trial was undertaken to evaluate compensatory growth in channel catfish and to chronicle the changes in body condition associated with the imposed feeding strategy. Four 1200-L circular tanks were each stocked with approximately 600 fingerling channel catfish (mean initial weight 32 g). Two tanks represented control fish which were fed to apparent satiation once daily throughout the trial. The two remaining tanks of fish were unfed for 4 wk and subsequently refed daily to apparent satiation for the following 10 wk in order to elicit a compensatory growth response. Fish fed to apparent satiation during the first 4 wk of the trial had a 41% increase in body weight, while the fasted fish decreased in weight by 20%. During the subsequent refeeding period, previously unfed fish were not able to increase growth rates sufficiently to overcome weight loss imposed by the 4-wk feed restriction. However, after 8 wk of refeeding, total increase in body weight of the previously unfed fish was 179 % of initial weight and similar to that of control fish which gained 231 % of initial weight. Hepatosomatic index (HSI) and condition factor decreased rapidly during the fasting period and increased rapidly to control levels during subsequent refeeding. The intraperitoneal fat (1PF) ratio and muscle ratio responded more slowly to feed restriction with IPF ratio decreasing consistently after 2 wk feed restriction. Muscle ratio showed little effect from the 4-wk period of feed deprivation. It appears that not feeding channel catfish fingerlings for 4 wk is too long to induce a compensatory growth response that is optimal for aquaculture; however, HSI may be the index of choice for detecting when refeeding should begin to maximize compensatory growth.     

Sensory Analysis of Rainbow Trout,Oncorhynchus mykiss,Fed Enriched Black Soldier Fly Prepupae,Hermetia illucens

A growth trial and fillet sensory analysis were conducted to examine the effects of replacing dietary fish meal with black soldier fly (BSF) prepupae, Hermetia illucens, in rainbow trout, Oncorhynchus mykiss. A practical‐type trout diet was formulated to contain 45% protein; four test diets were developed by substituting 25 and 50% of the fish meal with normal (BSF) or fish offal‐enriched black soldier fly (EBSF) prepupae. Dietary fat was adjusted to approximately 20% lipid using fish oil and poultry fat. Diets were fed to three replicate tanks of fish per treatment (10 fish/tank) for 8 wk. After the trial, three fish per tank were sampled for determination of hepatosomatic index, intraperitoneal fat ratio and muscle ratio, and muscle proximate and fatty acid composition. Fish remaining after sampling were used for sensory evaluation. Growth of fish fed the EBSF diets was not significantly different from those fish fed the fish meal‐based control diet, while the growth of fish fed the BSF diets was significantly reduced as compared to the control diet. A group of 30 untrained panelists did not detect a significant difference in a blind comparison of fish fed the fish meal containing control diet as compared to fish fed the EBSF or BSF diets.     

Evaluation of ingredient combinations from differing origins (fishmeal,terrestrial animal and plants) and two different formulated nutrient targets on rainbow trout growth and production efficiency

A 12‐week trial was performed with rainbow trout (Oncorhynchus mykiss) utilizing combinations of ingredients at two nutrient targets. Ingredient combinations were fishmeal‐based diet (FMD), animal product‐based diet (APD), plant product‐based diet (PPD), novel plant‐based diet (NPD) and potential future plant‐based diet (FPD). Two nutrient concentrations were targeted: 1) to meet published amino acid targets for rainbow trout utilizing approximately 450 g/kg crude protein (400–420 g/kg digestible protein) and 2) to meet the amino acid targets based on ideal amino acid balance of trout muscle for Lys, Met and Thr utilizing approximately 400 g/kg crude protein (370–380 g/kg digestible protein). Interactive effects between ingredient combination and nutrient concentration occurred across all response variables. When diets were formulated to Target 1, fish consuming FMD and APD displayed better weight gain and feed conversion ratio (FCR) than plant‐based diet, while graded effects were found within the plant‐based treatments. When differing ingredient combinations were utilized and formulated to Target 2, fish grew equally well except for the NPD treatment which supported lower growth and higher FCR. Based on the data from the current experiment, one can completely remove fishmeal from trout feeds and reduce protein levels when dietary digestible amino acids are balanced.     

Impact of plant cell wall network on biodegradation in soil: Role of lignin composition and phenolic acids in roots from 16 maize genotypes

Residue quality is a key factor governing biodegradation and the fate of C in soil. Most investigations of relationships existing between crop residue quality and soil decomposition have been based on determining the relative proportions of soluble, cellulose, hemicellulose and lignin components. However, cell wall cohesion is increased by tight interconnections between polysaccharides and lignin that involve cross-linking agents (phenolic acids). The aim of this study was to determine the role of lignin composition and phenolic acids on short- to medium-term decomposition of maize roots in soil. Sixteen maize genotypes, presenting a range of chemical characteristics related to root lignin and phenolic acids, were used. The main components were characterized by Van Soest (VS) extraction and cell wall acid hydrolysis, and the non-condensed Syringyl and Guaicyl lignin monomers, esterified phenolic acids and etherified phenolic acids were determined. Maize roots were then incubated in soil under controlled conditions (15 °C, −80 kPa moisture) for 796 days. Results showed that VS extraction over-estimated the structural hemicellulose content and that VS lignin was more recalcitrant than Klason lignin. The tremendous effect of cell wall chemical characteristics was shown by marked variations (almost two-fold differences in C mineralization), between the 16 maize roots. Decomposition was controlled by soluble residue components in the short term whereas lignin and the interconnections between cell wall polymers were important in the long-term. Notably the cell wall domain rich in non-condensed lignin and esterified phenolic acids was prone to decomposition whereas the presence of etherified ferulic acids seemed to hamper cell wall decomposition.     

Limited response of ponderosa pine bole defenses to wounding and fungi

Tree defense against bark beetles (Curculionidae: Scolytinae) and their associated fungi generally comprises some combination of constitutive (primary) and induced (secondary) defenses. In pines, the primary constitutive defense against bark beetles consists of preformed resin stored in resin ducts. Induced defenses at the wound site (point of beetle entry) in pines may consist of an increase in resin flow and necrotic lesion formation. The quantity and quality of both induced and constitutive defenses can vary by species and season. The inducible defense response in ponderosa pine is not well understood. Our study examined the inducible defense response in ponderosa pine using traumatic mechanical wounding, and wounding with and without fungal inoculations with two different bark beetle-associated fungi (Ophiostoma minus and Grosmannia clavigera). Resin flow did not significantly increase in response to any treatment. In addition, necrotic lesion formation on the bole after fungal inoculation was minimal. Stand thinning, which has been shown to increase water availability, had no, or inconsistent, effects on inducible tree defense. Our results suggest that ponderosa pine bole defense against bark beetles and their associated fungi is primarily constitutive and not induced.     

Effect of protein source and nutrient density on growth efficiency, histology and plasma amino acid concentration of rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of protein source and nutrient density on growth efficiency, nutrient digestibility and plasma amino acid concentrations of rainbow trout were evaluated. A 3 by 2 factorial treatment design with three protein sources, fish meal–barley (F–B), plant concentrates (PC) and plant meals (PM), and two nutrient densities were used. A commercial reference diet was also fed. Triplicate tanks of 30 fish (initial wt. 28 g) were fed each diet, and the final weight averaged 240 g fish⁻¹. Protein source and nutrient density affected feed intake, weight gain and feed conversion ratio. Weight gain of trout fed the PC and PM diets was approximately 10% less than fish fed the F–B diets. Protein retention was affected by protein source, but not nutrient density, and was the highest for the fish fed diets containing fish meal and the lowest for the fish fed PM diets. Apparent digestibility coefficients and apparent amino acid availabilities of the diets corresponded with differences in weight gain. This study provides further evidence that growth rates of trout fed fish meal‐free diets, using conventional and concentrated plant protein ingredients, are good but some limitation to growth exists in the fish meal‐free diets.     

Lysine supplementation of commercial fishmeal‐free diet in hybrid striped bass Morone chrysops x M. saxatilis affects expression of growth‐related genes

Our recent results in hybrid striped bass (HSB) concluded that ideal protein theory accurately predicts first‐limiting amino acids in commercial diet formulations if accurate amino acid availability data are used and that appropriate levels of supplemental lysine are needed to improve fish performance from fishmeal‐free diets. Our goal in this study was to elucidate how dietary lysine supplementation of a commercial fishmeal‐free diet influences the expression of two genes, myostatin and myogenin, controlling myogenesis in differentially growing groups of HSB. Real‐time RT‐PCR results in HSB suggest that the levels of lysine added to the diet (17.8, 35.1, 51.0 g kg^?1 of diet) has an impact on myogenin relative to the basal unsupplemented diet, but no effect on myostatin. Moreover, our data further suggest that the amount of dietary lysine supplementation influenced the ratio of myostatin/myogenin expression in HSB and that this pattern mimicked that of most of the growth, composition of growth and nutrient retention data from our previous study and may therefore be a useful marker for selecting fish for improved growth performance.     

Soil biodegradation of maize root residues: Interaction between chemical characteristics and the presence of colonizing micro-organisms

Due to their direct contact with the soil, roots are exposed to colonizing micro-organisms that persist after the plant has died. These micro-organisms may affect intrinsic root-chemical quality and the kinetics of root residue decomposition in soil, or interact with soil micro-organisms during the decomposition process. The aims in this work were i) to determine the interactions between the presence of root-colonizing micro-organisms and root-chemical quality and ii) to quantify the effect of these micro-organisms on root decomposition. Roots were selected from six maize genotypes cultivated in the field and harvested at physiological maturity. The roots of two genotypes (F2 and F2bm1) had a higher N content, lower neutral sugars content and higher Klason lignin content than the other genotypes (F292, F292bm3, Mexxal, Colombus). Location of the root residue micro-organisms by scanning electron microscopy and transmission electron microscopy revealed that F2 and F2bm1 roots were more colonized than roots of the other genotypes. Electron Dispersive X-Ray microanalyses of in situ N confirmed a higher N content in the colonizing micro-organisms than in the root cell walls. Residues of F2 and F2bm1 roots decomposed more slowly and to a lesser extent than those of the other genotypes during incubation in a silty loam soil under controlled conditions (15 °C, −80 kPa). After 49 days, 40.6% of the total C from F292 was mineralized but only 20.7% of from F2bm1. These results suggest that residue-colonizing micro-organisms decompose the cell-wall sugars to varying extents before soil decomposition thereby modifying the chemical quality of the residues and their mineralization pattern in soil. Due to their high N content, colonizing micro-organisms also impact on the total N content of root residues, reducing their C to N ratio. Gamma sterilized root residues were incubated under the same conditions as non-sterilized residues to see if micro-organisms colonizing root residues could modify the action of soil micro-organisms during decomposition. Similar C mineralization rates were observed for both non-sterilized and sterilized residues, indicating that the residue micro-organisms did not quantitatively affect the activity of soil micro-organisms.