Bent Rønsholdt

Gastrointestinal delivery of peptide and protein drugs to aquacultured teleosts

Abstract While one of the major roles of the vertebrate gut is to exclude antigens, it is generally accepted that a proportion of ingested protein is absorbed in an intact form and as small peptides. This review briefly examines the evidence for the occurrence of intact protein and peptide uptake in fish. Consideration is given to the mechanisms of absorption of macromolecules and an outline of the possible physiological function of the phenomenon over-viewed. The application potential of this natural occurrence to the oral delivery of production-oriented bioactive peptide and protein drugs is considered with reference to growth, reproduction and immunomodulation. Attention is drawn to specific methods which have been examined as a means of protecting macromolecules from the degradative action of the gut (e.g., anti-proteases, antacids) and or enhancing their uptake (e.g., mucosal modifiers). Finally, areas which offer potential for future research effort are presented, including consideration of design concepts for oral delivery methods and the need for increased understanding of the pharmacokinetics of production-related peptide and protein drugs.

The effect of vaccination and vaccine components upon short-term growth and feed conversion efficiency in rainbow trout

The impact of single intraperitoneal injections (0.2 ml) of a commercial vaccine, its components and a novel adjuvant upon growth and feed conversion efficiencies (FCE) of rainbow trout (n=35/tank in duplicate) was evaluated over a 7 week period. The vaccine contained a metabolisable oil-emulsion. Post hoc multiple comparison (Scheffes method) using a set of contrasts included (i) vaccination vs. control; (ii) Aeromonas salmonicida cells vs. no cells; (iii) adjuvant (metabolisable oil) vs. no adjuvant; (iv) interaction effect between A. salmonicida cells and adjuvant; (v) differences between adjuvants; and (vi) adjuvants vs. control. Vaccination resulted in significant (P<0.05) growth depression when compared to untreated controls. Over the duration of the trial, weight loss in vaccinated fish was 8%. Furthermore, it was determined that the effect of the vaccine upon growth was caused by cells (P<0.05) rather than adjuvant and/or interactions between the two. Also A. salmonicida cells caused a significantly (P<0.05) higher splenic index. Vaccination caused intra-abdominal adhesions and injection site lesioning.

Growth, feed utilisation, carcass composition and sensory characteristics of rainbow trout treated with recombinant bovine placental lactogen and growth hormone

The effect of treating rainbow trout (initial weight=51 g, T=10–11.5°C, fed to satiation), with recombinant bovine placental lactogen (PL, 2 μg g−1 body weight week−1) or growth hormone (GH, 2 μg g−1 body weight week−1), upon growth, feed conversion, sensory characteristics and fillet composition was investigated, with reference to three control groups. Hormone treatments were given for a period of 5–6 weeks, followed by a period of 13 weeks during which animals were left undisturbed. Differences in proximate composition of carcass (P<0.0005) and entrails (P<0.01), but not skeleton, were observed when sampled fish (PL at 5 weeks, GH at 6 weeks, and control at 7 weeks) of similar length were compared. At trial termination, eight animals from each group were randomly caught and slaughtered. The left fillet of each fish was skinned, vacuum-packed and boiled for 5 min, while the right fillet was used for compositional analyses. A trained sensory panel for flavour, odour, texture and appearance examined boiled fillets. PL-treated fish were deemed to express superior characteristics to control or GH-treated trout, particularly for juiciness (P<0.05). GH-treated animals received lower scores (P<0.05) for both sweet odour and flavour. Concurrent with a higher score for dryness, GH-treated fish returned higher fillet protein content (P<0.05) than other groups.

Effect of Growth Hormone and Salbutamol on Growth Performance, Fillet Proximate Composition and Pigmentation of Rainbow Trout (Oncorhynchus mykiss).

Growth hormone (GH) and salbutamol were employed to manipulate protein and lipid turnover in rainbow trout. The effect of these treatments upon growth and their impact upon pigmentation, proximate composition and production yield was examined. The experiment was conducted in two steps: a 6-week restricted feeding experiment with 336 fish (mean weight 461 g, S.D.=61 g) in 16 tanks, followed by a 4-week satiation feeding experiment with 224 fish (range 400–600 g). GH (dose 5 mg kg−1 body weight, bi-weekly, i.p.-injected) and salbutamol (dose 5 mg kg−1 feed) were randomly assigned in a 2×2 factorial with four replicates, each of which consisted of diets containing either 0 mg astaxanthin, 16.7 mg astaxanthin, 33.3 mg astaxanthin or 50 mg astaxanthin/kg feed. Feed consumption was measured daily and weight and length measured bi-weekly. Mean length was greater (P=0.005) in GH-treated animals (36.7 vs. 36.3 cm, S.E.M.=0.8 cm) at the end of the restricted feeding experiment, whereas both mean length and weight were greater (P<0.0005) at the end of the satiation feeding experiment (39.9 vs. 39.2 cm, S.E.M.=0.8 cm, and 975 vs. 930 g, S.E.M.=6 g). Salbutamol modified fish growth patterns but not end length and weight. Feed conversion ratios (FCR) were lower (P=0.044 and P=0.0003, respectively) for GH-treated fish after restricted (GH: 0.84 and GH+salbutamol 0.82 vs. control: 0.86 and salbutamol: 0.85; S.D.=0.028) and satiation feeding phases (GH: 0.89 and GH+salbutamol 0.94 vs. control: 1.00 and salbutamol: 1.01; S.D.=0.039). Although no overall effect of salbutamol treatment was seen, the FCR for salbutamol-treated fish improved during the restricted feeding phase, resulting in lower (P=0.03) FCR during the third bi-weekly period of this phase (salbutamol: 0.90 and GH+salbutamol: 0.86 vs. control: 0.95 and GH: 0.94; S.E.M.: 0.014). GH treatment reduced fillet pigmentation. This effect was most pronounced in fish receiving 16.7 mg astaxanthin/kg feed (1.91 vs. 2.33 mg astaxanthin-equivalents kg−1 fish, S.D.=0.35, P=0.0037), less when fed 33.3 mg/kg feed (3.13 vs. 3.65 mg astaxanthin-equivalents kg−1 fish, S.D.=0.50, P=0.012), but was without effect on fish fed 50 mg/kg feed (3.94 vs. 4.48, S.D.=1.16, P=0.25). Neither GH nor salbutamol affected visceral-somatic index (VSI), proximate composition or fillet colour.