Control of the somatic growth in turbot

Abstract

The development of a recombinant turbot somatotropin (rtuGH) in Escherichia coli and an homologous antibody in rabbit has produced a sensitive and specific RIA allowing the measurement of blood levels and pituitary contents of tuGH and their responses to environmental change. Turbot IGF-1 (insulin growth factors) and IGF type 1 receptor (R) cDNA have also been cloned and sequenced. The deduced IGF-1 R primary sequence contains all the topological features characteristics of mammalian IGF-1 R and the turbot R appears highly conserved, compared to its mammalian counterpart, particularly within the catalytic domain. IGF-1 R mRNA polyadenylation status varies during development with polyadenylation occuring in oocytes and early stage larvae. It disappears in later stages and in adult somatic tissues, indicating that IGF-1 R mRNA undergoes complex post-transcriptional regulation. Thyroid hormones (TH, both T 3 and T 4 ), are also involved in growth control, but are less affected by environmental changes than GH, except in very extreme conditions. The thyroid stimulating hormone (TSH) -subunit cDNA fragment has also been cloned and sequenced. mRNA expression levels have been quantified under conditions where blood circulating TH were modified by dietary treatments or hormone supplementation. Specific growth rate in turbot is related to food intake and is doubled with a temperature increase from 8 to 20 C. Lipid storage by contrast was higher at low temperatures. Over a long time course, growth rate in turbot can be improved in brackish water (8-20 psu) but it cannot adapt to very low salinities. Photoperiod appears to have little influence on growth when feeding is unrestricted. Under intensive farming conditions, ammonia, the major nitrogen waste product in teleosts, may increase to levels that can reduce growth. Safe ambient levels for growth are <2-3 mg l 1 TAN above which a 10-20% decrease in growth was recorded within 3 months. Over 20 mg l 1 , feeding stops and no growth occurs. Turbot juveniles can cope efficiently with relatively large fluctuations in ambient oxygen, but major disruptions to physiological functions occur below 20% of air saturation. Under moderate hypoxia growth is reduced by 20% within 1·5 months. The primary response to hypoxia or ammonia accumulation is always a decrease of food intake. 1999 The Fisheries Society of the British Isles

Impacts of hypoxia on the structure and processes in pelagic communities (zooplankton, macro-invertebrates and fish)

“…The growth rates in American winter flounder (Pseudopleuronectes americanus) kept in hypoxic waters were less than 50% of those kept under normoxic conditions (Bejda et al, 1992). Similarly, moderate hypoxic conditions caused a 20% reduction in growth of turbot (Boeuf et al, 1999). Chabot and Claireaux (2008) confirmed this threshold in laboratory studies and demonstrated that growth and food ingestion of Atlantic cod were significantly reduced below 70% saturation.…”

“…These fish cope with low-oxygen conditions by reducing one of their physiological activities, growth. The underlying mechanism is likely to be a reduction in food intake (Boeuf et al, 1999;Pichavant et al, 2001). A decrease in ingestion may reduce the energy demands and therefore the oxygen requirements.…”

Current growth, fat reserves and somatic condition of juvenile Baltic herring (Clupea harengus membras) reared in different salinities

“…In experimental conditions, this species achieved better growth in salinity of 5-10 ppt than in 28-34 ppt, where adult live (Hettler 1976). In marine turbot, Scophthalmus maximus, brackish water (8-20 psu) enhanced somatic growth (Boeuf et al 1999), whereas in juvenile sturgeon, Acipenser brevirostrum, the growth rate was highest in fresh water.…”

“…Many studies have shown that salinity affects euryhaline fish in multiple ways; e.g., their behaviour, intake of food, food conversion rate, somatic condition, fat reserves, growth and survival (e.g., Peterson-Curtis 1997;Boeuf et al 1999;Peterson et al 1999;Atwood et al 2001;Jarvis et al 2001;Cordier et al 2002). Euryhaline species usually tolerate a wide range of salinities as adults, but they have a given optimum, where they perform best growth.…”

“…These parameters have been determined in euryhaline fish species, in order to find out their optimum salinity at juvenile or adult stages (e.g., Hettler 1976;Boeuf et al 1999;Jarvis et al 2001;Imsland et al 2001Imsland et al , 2003. Experimental studies with adult or juvenile Baltic herring have not been made previously (Westin and Aneer 1987), partly because the herring is highly sensitive to handling stress and difficult to keep in captivity for long periods (Blaxter and Holliday 1963).…”