E. McLean

Absorption of Bioactive Proteins by the Gastrointestinal Tract of Fish: A Review

Abstract A review of the literature pertaining to the ability of the fish gastrointestinal tract to absorb biologically active proteins is presented. Consideration is given to the transcellular and paracellular processes (both real and potential) by which intact proteins may gain access to the internal milieu. Quantitative aspects of protein absorption and data relating to the time course of appearance in the blood of lumenally presented, biologically active proteins are compared in both gastric and agastric teleost species. The significance of the gastric and pancreatic barriers to protein uptake is also examined. Proposals concerning the physiological significance (if any) of this natural process are evaluated. Finally, oral delivery of production-oriented pharmaceuticals comprising biologically active proteins (e.g., vaccine preparations and somatotropins) is considered for use in aquaculture.

Impact of a controlled release formulation of recombinant bovine growth hormone upon growth and seawater adaptation in coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon

Abstract Experiments were undertaken to evaluate a sustained release recombinant bovine growth hormone (rbGH) formulation (Posilac®) in salmon. The investigation was divided into two parts. The first series of studies was used to establish optimal dosages and clearance rates for the exogenous protein in size-selected coho salmon, and to examine the effect of rbGH treatment upon smoltification. The second series of studies attempted to mimic the production setting, where chinook salmon were randomly selected from a stock of animals, and taken through smoltification to grow-out. In the first experiment, coho salmon were provided with a single injection of one of three doses (420, 1260, 4200 μg/g body weight equivalent) of the rbGH preparation (n ≥30/group), or were injected with a saline solution containing the high dose equivalent of rbGH. Controls were treated with BSA, given one of three (10, 30 or 100 μl) placebo carrier preparations without rbGH, or left untreated. Animals receiving rbGH by sustained-release expressed highly significant (P

Growth acceleration of coho salmon (Oncorhynchus kisutch) following oral administration of recombinant bovine somatotropin

Abstract The growth response of juvenile coho salmon to injected or orally administered recombinant bovine somatotropin (rbst) was examined; rbst was delivered orally either alone or with an antacid and putative penetration enhancer. Oral delivery of 12.5 μg rbst/g body wt per week resulted in accelerated growth in weight, over a 7-week period, when compared to three control treatments. Coadministration of the same dose of rbst with antacid and a penetration enhancer provided enhanced weight gain when compared to unprotected orally delivered rbst, and the growth matched that of fish injected with 2.5 μg rbst/g body wt per week during the study.

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.

Accelerated growth of coho salmon Oncorhynchus kisutch following sustained release of recombinant porcine somatotropin

Five groups of coho salmon (67.0 ± 4.7 g wet weight) were implanted with one of four types of somatotropin-containing slow-release pellets or a placebo. Following implantation, the growth response of each group was recorded over 6 months. All groups in receipt of recombinant-porcine-somatotropin (rpst) therapy exhibited significant growth acceleration (37–83% greater than controls, P < 0.05). Rpst therapy had a marked effect upon relative intestinal length; but no effect upon hepato- or visceral-somatic indices. At the end of the experimental period, all groups exhibited similar condition factors, percent body moisture and protein content. However, between-group differences in lipid content were recorded.

Antisomatostatin-induced growth acceleration in chinook salmon (Oncorhynchus tshawytscha).

Since somatostatin (SRIF) inhibits the release of growth hormone (GH), its immunoneutralization may provide an alternative to GH therapy as a means of enhancing somatic growth in fish. The present study examined the feasibility of accelerating growth in juvenile chinook salmon by means of antiSRIF administration. Yearling salmon of Nicola River stock (BC, Canada) were injected intraperitoneally every 5 days, for a total of 40 days, with either SRIF (1 μg g-1 body wt.), antiSRIF (SOMA-10, 1 μg g−1), recombinant bovine GH (rbGH, 2.5 μg g−1), recombinant porcine GH (rpGH, 2.5 μg g−1) or saline (controls). No significant differences were observed in length, weight or final condition factor (k) between the SRIF-treated and control fish over the experimental period. However, the fish treated with the antiSRIF were significantly (p ≤ 0.05) longer and heavier than the control salmon after 25 and 30 days respectively. Furthermore, antiSRIF treatment caused a lowering in k when compared to the control salmon. Fish injected with rbGH or rpGH were significantly longer and heavier than all other groups (p ≤ 0.05), after only 5 days. GH treated groups also returned higher k when compared against all other treatments (p ≤ 0.05). No differences were observed in growth between the two rGH treatments over the experimental period.

Evaluation of a sustained-release polymer-encapsulated form of recombinant porcine somatotropin upon long-term growth performance of coho salmon, Oncorhynchus kisutch

Abstract The effect of sustained-release recombinant porcine somatotropin (RPST) treatment upon growth performance of coho salmon was examined over a 95-week period. Animals were implanted with one of 4 types of RPST-containing capsules, or were placebo-treated as controls. The encapsulated RPST exhibited different liberation kinetics, in that protein release was inversely proportional to the thickness of the polymer coating. Fish implanted with pellets with the highest release rates for RPST during a 14-week period maintained a weight advantage over the control group until week 77, while the advantage in terms of length was maintained for 95 weeks. Specific growth rates (SGR) for weight were significantly greater in fish treated with the capsules which exhibited the highest RPST release over the first 26 weeks of the study when compared to controls. However, between weeks 26 and 52, weight SGR was similar in all groups. At trial termination, significant differences in relative intestinal length, visceral and gonadosomatic indices were noted between the group implanted with capsules expressing most rapid RPST release and the placebo-implanted fish. Significant decreases in body lipid levels, relative to initial values, were observed in fish implanted with capsules expressing the two highest release rates.

Comparison of hydrostatic pressure and thermal shocks to induce triploidy in coho salmon (Oncorhynchus kisutch)

Abstract Hydrostatic pressure or thermal shocks were administered to coho salmon eggs 20, 40, 60 and 80 min post-insemination. Pressure shocks ranged from 6.2 to 8.4×104 kPa, and lasted 4 min. Thermal shocks ranged from 24 to 28°C, and were applied for durations of 10 and 20 min. Triploid induction rate for each treatment group was evaluated by measurement of erythrocyte DNA content using flow cytometric analysis. Triploid rates of 100% were produced by pressure shocks of 6.9–8.3×104 kPa for eggs 20 min post-fertilization and by thermal trauma of 28°C for 20 min, 20 min after fertilization. Survival was inversely correlated with the intensity of treatments. Thus, triploid yields calculated as the product of the triploid rate and the numbers surviving to hatch, expressed as a percentage of the number of eggs originally present in the groups, were highest with a hydrostatic pressure treatment of 6.2×104 kPa for 4 min treatment, 20 and 40 min after fertilization or a heat shock of 26°C for 20 min treatment, 20 min after fertilization.

Triploidization of coho salmon following application of heat and electric shocks

Abstract The effectiveness of heat shocks in combination with electric shocks, derived from either alternating (AC) or direct sources (DC) (10 V), was compared with respect to their ability to induce triploidy in coho salmon. Electric shocks were applied to eggs for 2.5, 5.0 and 10 min duration, and for 10, 20 and 40 min post-fertilization, at 10 and 26°C. Control eggs received identical handling and heat treatments but without electric shocks. Treatment of developing embryos with AC currents was more effective in including triploidy than with DC current. AC shocks of 10 min duration, delivered to eggs held at 26°C, 40 min post-fertilization, produced 100% triploidization versus 70% and 15% observed in DC and control studies respectively. Ploidy states were verified by flow cytometric analyses.