Jack R. McBride

9 – Hormonal Enhancement of Growth

This chapter reviews the comparative endocrinology of the growth regulating hormones in fish and describes the research aimed at the application of the knowledge regarding fish culture. Three types of hormones have been shown to increase growth rates in fish both alone and in combination. These are the pituitary growth hormones, the anabolic steroid hormones, and the thyroid hormones. In addition to these, the insulins are a fourth group of hormones, which play a significant metabolic role and may be capable of growth promotion alone or in combination with other hormones. While pituitary materials have been collected from most classes of fish, they have only been tested for growth promoting activity in the teleosts, amphibia, or mammalia. Most of these fish pituitary preparations have been tested in the mammalia, specifically in the rat tibial plate assay. Of the various classes of fish, only the teleostei have been used as bioassay recipients for growth hormone preparations from other vertebrates. It is clear from the range of donor and recipient response relationships shown in the chapter that the growth hormone of teleosts is distinct from that of other vertebrates including the other classes of fish.

Application of thyroid and steroid hormones as anabolic agents in fish culture

A basic premise in any intensive culture system is to maximize growth at minimum cost, with an end product that is of high nutritive value and aesthetically acceptable to the consumer. This review is directed towards evaluating the role for thyroid hormones and steroids in fish culture. Particular attention has been given to the following topics: growth, appetite, food conversion, carcass composition, salt water tolerance, species specificity, deleterious responses and economic implications.

The effects of hypophysectomy in the rainbow trout Salmo gairdnerii (Rich.) with special reference to the pituitary-interrenal axis

Abstract A method for the hypophysectomy of rainbow trout ( Salmo gairdnerii ) is desribed. Hypophysectomy resulted in a marked atrophy of the interrenal and thyroid tissue, a cessation of spermatogenesis, and an absence of proliferation of the integument. The plasma cortisol concentration in sham hypophysectomized fish averaged 8.1 μg/100 ml. One day after hypophysectomy the cortisol concentration averaged 3.6 μg/100 ml. Plasma samples taken from 2 to 17 days after hypophysectomy had an average cortisol concentration of 1.6 μg/100 ml. Stress caused a significant increase in the plasma cortisol concentration of control fish, but not of hypophysectomized fish. Sham operated trout injected with dexamethasone 1 mg/kg intraperitoneally 20 hours prior to blood sampling had a plasma cortisol concentration identical to that of uninjected hypophysectomized fish. These data indicate that interrenal function in S. gairdnerii is under pituitary control and that a negative feedback mechanism probably operates between the interrenal and the pituitary.

Assessment of undephytinized and dephytinized rapeseed protein concentrate as sources of dietary protein for juvenile rainbow trout (Oncorhynchus mykiss)

Abstract This study was undertaken to evaluate three sources of rapeseed protein concentrate (RPC) as partial or total replacements of steam-dried whole herring meal (HM) in a practical diet for juvenile rainbow trout. Groups of 4.2–4.4 g trout held in 10.0–10.3°C well water on a natural photoperiod were fed one of 10 isonitrogenous (43% protein) and isoenergetic (21.6 MJ gross energy/kg) diets to satiation 3 times daily. Each of three test protein sources, viz. undephytinized, untreated control RPC (UDC), undephytinized solvent-treated control RPC (UDSC), and dephytinized RPC (DP), comprised about 19.0, 39.0 and 59.0% respectively of dietary protein by replacement of one-third (L), two-thirds (M) and all (H) of the HM protein in the control diet. Rainbow trout growth rate, feed intake, feed efficiency, protein and gross energy utilization, mortality and health were not compromised when either UDC or DP replaced up to 66% of HM protein in the control diet. Total replacement of HM protein with each of the RPC sources did not depress feed intake, but did significantly reduce growth rate, feed efficiency, and protein and energy utilization. The procedure used to dephytinize RPC lowered RPC protein quality. Whole body concentrations of calcium and phosphorus were inversely related to the dietary levels of UDC and UDSC. Body levels of zinc were significantly depressed in fish fed the diet with UDSC-H. Fish fed diets with DP displayed normal mineral levels. Significant elevation of thyroid follicle epithelial cell heights was found only in those groups fed the diets with UDC-H or UDSC-H. Whole body proximate composition was generally uninfluenced by diet treatment. It is concluded that RPC can comprise 39% of the dietary protein (fish meal only 11%) for rainbow trout without adversely affecting performance. Nutritional strategies that may enable complete replacement of fish meal protein in diets for rainbow trout by RPC are outlined.

Evaluation of Tower and Candle rapeseed (canola) meal and Bronowski rapeseed protein concentrate as protein supplements in practical dry diets for juvenile chinook salmon (Oncorhynchus tshawytscha)

Abstract A laboratory study and a pilot-scale hatchery experiment were carried out to determine the acceptability of rapeseed products as protein supplements in diets for chinook salmon. Replacement of 10 and 13% of the protein in a modified Abernathy dry diet with protein from Tower or Candle rapeseed meal or Bronowski rapeseed protein concentrate did not alter growth rate, food or protein utilization, body composition, thyroid or pituitary cytology, osmoregulatory capacity, health or mortality of chinook salmon. However, growth rate and food (protein) utilization were reduced when 25% of protein was replaced by rapeseed meal, but not when replaced by Bronowski rapeseed protein concentrate. Condition factors of chinook fed rapeseed products at the intermediate or highest levels were often significantly elevated. Hatchery performance of chinook salmon fed a dry diet where 13% of protein was provided from Tower meal was similar to that when Oregon moist pellets were fed except for a compensatory increase in thyroid activity in the former fish. It is concluded that rapeseed products of the canola type are good protein supplements for chinook salmon and can comprise 13 to 16% of dietary protein (16 to 20% of dietary dry matter).

Protein quality of Altex canola meal for juvenile chinook salmon (Oncorhynchus tshawytscha) considering dietary protein and 3,5,3′-triiodo-L-thyronine content

Abstract Juvenile chinook salmon, reared in freshwater, were fed isocaloric dry diets varying in protein (29, 39 and 49%), Altex canola meal (0, 11.5 and 23% of dietary protein by replacement of fish meal) and 3,5,3′-triiodo-L-thyronine (T 3 ; 0, 5 and 25 ppm) content. Oregon moist pellets (OMP) served as a reference control diet. Fish were subsequently observed in seawater while fed OMP. The nutritive value of herring and canola meal was similar when diets contained 29 and 39% protein, but not when protein content was 49%. Chinook fed 49% protein diets grew significantly faster than those fed diets with 29% protein. Appetite and protein utilization were inversely related to dietary protein content. Chinook fed OMP grew faster than those fed 49% protein diets with canola meal, but not when canola meal was deleted. T 3 stimulation of growth of chinook fed 49% protein diets was positively correlated with the dietary concentration of canola meal and T 3 . Dietary and hormonal treatment in freshwater did not influence chinook performance in seawater. Further, thyroid hypertrophy observed in fish fed diets with canola meal during freshwater residency did not persist after 5 weeks in seawater. It is concluded that Altex canola meal may comprise almost 25% of dietary protein without adversely influencing protein quality, provided that dietary glucosinolate content is below 2.65 μmoles/g dry diet (300 μg/g as 3-butenyl isothiocyanate). Dietary canola meal concentrations of 30% of dry matter (glucosinolate content > 2.65 μmoles/g dry diet) can be employed if 5 ppm of T 3 are administered simultaneously.

Thyroid and steroid hormones: Potential for control of growth and smoltification of salmonids

Abstract This overview provides the fish culturist with an insight into the potential and limitations for the use of orally administered growth promoters in the culture of anadromous salmonid smolts. Androgens, with the exception of 4-chlorotostosterone, at concentrations of 1 to 10 mg/kg in the diet have been shown to be effective anabolic agents in three species of the genus Oncorhynchus ( O. nerka, O. kisutch and O. tshawytscha ). These anabolic agents, however, have not been effective in two species of the genus Salmo ( S. salar and S. gairdneri ). In studies where a growth response was obtained with the anabolic agent a significant improvement was often recorded in feed conversion. Generally the estrogens are not effective as growth promoters. Ethylestrenol, however, did induce an increase in body weight when administered orally to S. salar . T 3 (3,5,3′-triiodo-L-thyronine) has only recently attracted attention as a potential growth promoter in anadromous salmonids. To date, positive growth responses have been reported with T 3 as a diet supplement in O. kisutch, O. tshawytscha, S. salar and S. gairdneri . The potential for anabolic steroids and(or) T 3 in the production of zero-age smolts, as well as in promoting the growth of undersized parr, is considered.

Efficacy of canola oil, pork lard and marine oil singly and in combination as supplemental dietary lipid sources for juvenile coho salmon (Oncorhynchus kisutch)

Abstract Canola oil, pork lard and herring oil singly and in combination were assessed as supplemental sources of dietary lipid for juvenile coho salmon held at 10–12°C on a natural photoperiod over an 84-day period. Each of the six different types of supplemental lipid comprised about 56% of the lipid content (15% of dry matter) in an experimental dry diet (West Van 1). Some groups received Oregon moist pellets (OMP) which is presently the standard hatchery diet. All groups were fed twice daily to satiation. Relative to coho fed West Van 1 with marine oil alone, type of supplemental lipid did not influence coho growth, food, protein and energy utilization, body proximate composition, fish health or survival, or the histological structure of selected organs. Coho fed OMP grew significantly faster than those fed West Van 1 supplemented with lard or mixtures of canola oil with herring oil or lard due to increased appetite. Body lipid composition mirrored that of dietary lipids except levels of saturated and unsaturated fatty acids showed less variation than those in dietary lipids. It is concluded that canola oil, pork lard and a blend of these lipid sources are excellent alternative types of supplemental dietary lipid for coho salmon under our test conditions. They are more available, often less expensive, and less prone to oxidation than marine oil.

Development of nutritional and environmental strategies for maximizing the growth and survival of juvenile pink salmon (Oncorhynchus gorbuscha)

Abstract The efficacy of varying diet moisture content (hardness) and composition and time of seawater entry in relation to swim-up was assessed over a 42-day period. Six dietary treatments and four seawater transfer times (2, 12, 22 and 32 days post swim-up) were tested. All groups were fed their prescribed diets 10 to 12 times daily to excess. Throughout the study a natural photoperiod was provided. Well water and seawater temperatures were 10–12°C and 9.5°C, respectively. Seawater salinity varied between 26 and 28‰. Best growth and biomass during culture were noted for groups fed dry (∼ 10% water) or intermediate moisture content (∼ 20% water) diets comprised of high nutritive value components, i.e., steam-dried fish meal coupled with a high level of freeze-dried zooplankton. Moreover, survival and biomass were observed to be inversely related to time of seawater entry after swim-up, regardless of diet treatment. Pink fry fed conventional hatchery foods, i.e., Oregon moist pellets, Biodiet and an experimental dry diet comprised of practical ingredients had poorest growth at all seawater transfer times. It is concluded that improvement of pink salmon performance via nutritional and environmental strategies offers potentially significant cost benefits to the fishing industry.

Diet composition as a factor in the anabolic efficacy of 3,5,3'-triiodo-L-thyronine administered orally to steelhead trout (Salmo gairdneri)

Abstract To assess the effect of diet composition on the anabolic efficacy of orally administered, 3,5,3′-triiodo-L-thyronine (T3), juvenile steelhead trout (Salmo gairdneri) were fed either a commercial dry diet (Silvercup) or an experimental dry diet with similar protein and gross energy contents. Lipid provided the major part of available non-protein energy in the former diet whereas carbohydrate (dextrin and glucose monohydrate) was the predominant source in the latter. After an initial 42-day period growth rate, appetite and protein efficiency ratios (PER) were similar for groups fed the two basal diets without hormone supplements. Terminal moisture content was significantly reduced and lipid content increased in fish fed the experimental diet. These fish also had a significantly elevated hepatosomatic index (HSI) and histological examination indicated a high degree of hepatic lipid or glycogen deposition. Supplementing the Silvercup diet with 1 or 5 ppm of T3 did not significantly affect growth rate, appetite, PER, protein conversion efficiency (PCE) or energy conversion efficiency (ECE). However, 25 ppm of T3 induced a small but statistically significant increase in weight. Fish fed the experimental diet, on the other hand, responded to T3 supplementation (1, 5 and 25 ppm) with significant increases in weight and length. PER increased in proportion to the T3 dose. Increases were also noted in PCE and ECE. Whole body protein and moisture content increased but lipid content and HSI decreased in the 25 ppm group. A highly variable enlargement of thyroid follicle epithelial cells was noted in all fish administered T3. Dietary T3 affected external morphology to a degree proportional to the T3 dose. We conclude that diet composition has a pronouced influence on the anabolic efficacy of oral T3. Also, our data suggest that oral T3 stimulates growth of steelhead trout through increased carbohydrate utilization.