Fish Physiology and Biochemistry

The molecular cloning of a cDNA encoding the pejerrey brain cytochrome P450 aromatase (P450aromB) is described. This form shares higher identity to other brain aromatases than with their respective ovarian counterparts and the self ovarian aromatase. Tissue-specific expression of both aromatases was examined in pejerrey by RT-PCR. The immunocytochemical distribution of P450aromB was described.

Mangrove red snapper fed advanced broodstock diets containing squid meal and squid oil exhibited higher hatching rates, cumulative survival and survival activity index than those fed a basal diet or a basal diet supplemented with mixture of antioxidants. On the other hand, fatty acid analyses of ovaries and fry of wild fish and eggs and larvae of broodstock fed raw fish revealed high arachidonic acid (ARA) and docosahexaenoic acid (DHA) levels and relatively lower eicosapentaenoic acid (EPA) levels consequently showing high ARA/EPA and DHA/EPA ratios compared to cold water species. This suggests that ARA may be nutritionally more important for egg and larval development and survival in tropical marine fish and its supplementation in broodstock diets may enhance reproductive performance of mangrove red snapper.

Plasma cortisol levels and the number (Nmax) and affinity (Kd) of specific hepatic cortisol-binding sites were determined in rainbow trout subjected to chronic confinement stress for 14 days. Confinement significantly elevated plasma cortisol levels to 47.3 ± 13.5 ng ml−1 within 24h and although levels declined to 8.0 ± 3.0 ng ml−1 after 14 days, they were significantly higher throughout than levels in unstressed control fish (< 2.0 ng ml−1). There was a 60% reduction in cytosolic Nmax in stressed fish during the first 24h of confinement (35.8 ± 7.9 cf. 129.0 ± 15.2 fmol mg−1 protein), a decline which was sustained at 7 days after the onset of stress but, although numbers of binding sites in the liver of stressed fish were still lower than in unstressed fish, the difference was no longer significant after 14 days of confinement. There was an accompanying significant rise in the Kd of cortisol binding in stressed fish during confinement, from 4.0 ± 0.6 nM at time 0 to 8.4 ± 0.8 nM after 24 h confinement. This increment in Kd was sustained at a level significantly higher than in control fish throughout the 14 day confinement period, despite marked reductions in cortisol levels and increases in Nmax in stressed fish. Throughout the study, specific binding of cortisol could not be consistently detected in high-salt nuclear extracts from stressed or unstressed fish, suggesting either that high-affinity binding sites for cortisol were absent from these preparations, that receptors were present but unable to interact with ligand because they were occupied, or that receptors were present but not being extracted. These possibilities were investigated using a range of extraction procedures, by varying the temperature of incubation, by employing dexamethasone as ligand and by examining binding in purified, intact, nuclei. Estradiol was employed as a methodological control throughout and substantial amounts of specific estradiol binding were detected in all compartments and preparations. Specific cortisol-binding sites were detected in intact nuclei of both stressed and unstressed fish, at levels an order of magnitude lower than estradiol binding in the same preparations. These data demonstrate that activation of the pituitary-interrenal axis leads to significant changes in the nature of target-tissue binding of cortisol in rainbow trout, and reveal a clear difference in the subcellular distribution of binding-sites for estradiol and cortisol, which reflects the situation in mammalian tissues.

The impact of increased incorporation of plant ingredients on diets for rainbow trout was evaluated in terms of gene expression of gastric (gastric lipase, pepsinogen) and intestinal (prolidase, maltase, phospholipase A2) digestive enzymes and nutrient transporters (peptide and glucose transporters), as well as of postprandial levels of plasma glucose, triglycerides and total free amino acids. For that purpose, trout alevins were fed from the start of exogenous feeding one of three different experimental diets: a diet rich in fish meal and fish oil (FM–FO), a plant-based diet (noFM–noFO) totally free from fish meal and fish oil, but containing plant ingredients and a Mixed diet (Mixed) intermediate between the FM–FO and noFM–noFO diets. After 16 months of rearing, all fish were left unfed for 72 h and then given a single meal to satiation. Blood, stomach and anterior intestine were sampled before the meal and at 2, 6 and 12 h after this meal. The postprandial kinetics of gene expression of gastric and intestinal digestive enzymes and nutrient transporters were then followed in trout fed the FM–FO diet. The postprandial profiles showed that the expression of almost all genes studied was stimulated by the presence of nutrients in the digestive tract of trout, but the timing (appearance of peaks) varied between genes. Based on these data, we have focused on the molecular response to dietary factors in the stomach and the intestine at 6 and 12 h after feeding, respectively. The reduction in FM and FO levels of dietary incorporation induced a significant decrease in the gene expression of gastric lipase, GLUT2 and PEPT1. The plasma glucose and triglycerides levels were also reduced in trout fed the noFM–noFO diet. Consequently, the present study suggests a decrease in digestive capacities in trout fed a diet rich in plant ingredients.

Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower growth rate of females. When females and males are considered separately, the growth rate is not significantly different in diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and 17β-estradiol (E2)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but the difference is not always significant. Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months compared to the triploid females and diploid males. 3,5,3′-triiodo-L-thyronine (T3) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in 4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth rate of males may be related to the high circulating levels of T3 and 11kT.

To better understand the endocrine- and immune-response pattern during reproduction in a fish species having parental care behaviors and also to accumulate the endocrine- and immune-related data for future explanations of the low reproductive efficiency in seahorse species, the variations of immune factors and sex steroids in the plasma of the male lined seahorse Hippocampus erectus at different breeding stages, i.e., pre-pregnancy, pregnancy (early, middle, and late periods), and post-pregnancy, were investigated in the present study. The immune factors included monocytes/leucocytes (M/L), leucocyte phagocytic rate (LPR), immunoglobulin M (Ig M), interleukin-2 (IL-2), interferon-α (IFN-α), and lysozyme (LZM). The sex steroids included testosterone (T), 11-ketotestosterone (11-KT), 11β-hydroxytestosterone (11β-OHT), 17α-methyltestosterone (17α-MT), 17β-estradiol (E2), and 17α-hydroxy-20β-dihydroprogesterone (17α-20β-P). Moreover, the immune metabolic activity of epithelium cells in the brood pouch at different breeding stages was also analyzed through ultrastructural observations of the abundance of cytoplasmic granules, mitochondria, endoplasmic reticulum, lysosomes, and exocytosis. The results show that a higher immune level was observed during pregnancy, particularly in the early and middle periods, and a lower immune level was noted during pre-pregnancy. Correspondingly, the epithelium cells in the brood pouch also showed a stronger immune metabolic activity during pregnancy and weaker activity during pre-pregnancy. Four sex steroids of T, 11β-OHT, 17α-MT, and E2 were higher during pre-pregnancy and lower during post-pregnancy, whereas 11-KT and 17α-20β-P, which were positively correlated with part immune factors, were higher during pregnancy. No negative correlations between sex steroids and immune factors were observed. In conclusion, the higher immune competence during pregnancy may indicate that parental care could improve immunity, which may be the major factor for no immunosuppressive effect of sex steroids during reproduction in the seahorse H. erectus, unlike noncaregiving fishes in which inhibitions of sex steroids on immunity are frequently observed. Moreover, higher 11-KT and 17α-20β-P during pregnancy than during pre-pregnancy and post-pregnancy may suggest that these two steroids are also involved in parental care regulation.

Sharks are not only threatened, but also have a low fecundity as they are being overfished. The shark family, Sphyrnidae, consists of nine species of which three are found in South African oceans. One of the three Sphyrnidae species, the scalloped hammerhead (Sphyrna lewini) are the most common, but their biology and mode of reproduction are not extensively studied in terms of their reproductive biology. The aim of this study was to describe the germ cell development in the testes of sexually mature male scalloped hammerheads. Three individual male S. lewini were caught at Zinkwazi, KwaZulu-Natal, South Africa. The sharks and their reproductive organs were weighed and measured to collect the biometric data for the condition factor and the gonado-somatic index. Following standard necropsy, the testes were fixed in Bouin’s solution and processed for histological assessment. The histological assessment revealed that the testes of S. lewini consist of seminiferous tubules which form part of a larger lobular structure with germ cells in different stages of development, from spermatogonia to mature spermatozoa. Seven stages of development were identified during the process of spermatogenesis, similar to what has been described for elasmobranchs. In conclusion, this study provides evidence that the testes of S. lewini are diametrical and polyspermatocystic and conforms to the testes structure of elasmobranch males.

The aim of this study was to investigate the survival rate, biochemical indices, and metabolome changes of the large yellow croaker after 48 h of live transportation. Two hundred and forty large yellow croakers (body weight: 23.4 ± 5.3 g, total length: 12.2 ± 0.7 cm) were used in this experiment. The transport buckets were filled with fresh seawater and the parameters of the water were a temperature of 16 ± 0.5 °C and a dissolved oxygen content of 6.0–7.2 mg/L. Large yellow crokers were first divided to 0, 10, 20, and 30 mg/L MS-222 groups to observe the 12 h survival rate. The survival rate of 10 mg/L MS-222 group (T1) was the 95%, highest of all, and was further analyzed. The results of liver biochemical indices indicated inhibition of gluconeogenesis and pentose phosphate pathway metabolism. In addition, metabolomics analysis identified significantly differentially expressed metabolites between T1 group and 0 mg/L MS-222 control (C) groups. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) results revealed that the pathways of amino acid metabolism, especially the lysine, aspartate, and homoserine in the liver were significantly affected. In conclusion, the combination of metabolomics and liver biochemical assays provided a characterization of the response mechanism of L. crocea exposed to live transportation.