Freshly fertilized ova, eyed ova and yolk-sac fry of brown trout, Salmo truifa L., were exposed to each of four trace metals (aluminium: 6000 nmol I -I ; copper: 80 nmol I-'; lead: 50 nmol I-'; zinc: 300 nmol I-I) while held in flowing artificial soft-water media maintained at pH 4.5 or 5.6 and [Ca] 20 or 200 pmol I-'. In continuous exposure from fertilization, survival of ova was severely affected at pH 4.5 and [Ca] 20 pmol I -I , regardless of the presence of Cu, Pb or Zn; A1 reduced embryonic mortality and improved hatching success. High ambient [Ca] at pH 4.5 increased egg survival. At ' swim-up ', surviving fry exposed to A1 or Pb had lower whole body Ca, Na and K content, irrespective ofpH or ambient [Ca]. Cu reduced whole body Ca and K content at pH 5.6 and [Ca] 200 pmol-I, and whole body Ca, Na and K content in the other media. Zn reduced whole body mineral content at pH 5.6 and [Ca] 20 pmol I-'. Whole body Mg content was reduced by all trace metals at pH 5.6 and [Ca] 20 pmol I-', and by Cu at pH 5.6 and [Ca] 200 p o l I-I. Al and Cu impaired skeletal calcification at pH 5.6 at both ambient [Ca]; Pb only at [Ca] 20 pmol I-'. Zn enhanced calcification at pH 4.5 and [Ca] 200 pmol I-'. In the absence of trace metals, low pH reduced body Ca, Na, Kcontent and skeletalcalcificationat [Ca] 200 pmol I-'. The uptake ofCa, Na and K, measured at regular intervals from hatching was impaired to the same extent by all treatments at pH 4.5, irrespective ofambient [Ca] or trace metal presence. At pH 5.6, irrespective of ambient [Ca], Al, Cu and Pb impaired Ca and K uptake. The rate of Na uptake was reduced by A1 and Cu. Al-treated yolk-sac fry, exposed to low ambient [Ca] from 200-300"days post-hatch, suffered high mortalities regardless of pH. Ca, Na and K uptake was impaired by all treatments at pH 4.5, and by A1 and Cu at pH 5.6 in a similar exposure period. The development of the early stages of brown trout in the presence of trace metals is discussed in relation to recruitment failure in areas of soft. acid water.

SUMMARY1. The plasma volume in rats aged 15-16 days was measured by dilution analysis using homologous, 1251-labelled immunoglobulin G. A mean plasma volume of 5-53 ml./100 g and a mean blood volume of 8-01 ml./100 g were obtained.2. After the injection of labelled immunoglobulin G into the heart, homogenates of various abdominal organs and of the carcass were prepared. Labelled immunoglobulin G left the vascular compartment at a rate of about 9-10 %/hr over a 3 hr period. About 11 % of the labelled immunoglobulin G was catabolized in 2 hr.3. The data obtained from these studies was used to make quantitative estimates of the amount of intact immunoglobulin G transmitted from the proximal intestine and from the ileum after the intra-intestinal injection of 1000 ug of labelled immunoglobulin G. Homogenates of the experimental animals were prepared and it was estimated that over 40 % of the labelled immunoglobulin G was transmitted as intact protein from the proximal intestine. The results suggest that no intact immunoglobulin G was transmitted from the ileum, but about 15 % of the protein removed from the ileum was recovered in the whole body as degraded fragments precipitable with trichloroacetic acid.4. These observations are discussed in the context of the transmission of antibodies, and their relevance to the receptor hypothesis is considered.

SUMMARY1. 125I-labelled homologous IgG was injected into different regions of the small intestine of rats aged 12, 16, 18, 20 and 22 days. At 12 days the proximal and middle regions of the intestine readily absorbed globulin and transmitted it to the circulation. The distal region of the intestine transmitted little to the circulation at all ages tested.2. The intestine loses its ability to transmit globulin to the circulation in a distal-proximal direction. At 16 and 18 days the ability of the middle region had declined significantly, and this decline continued so that little globulin was transmitted from this region at 20 and 22 days.3. The proximal intestine retained the ability to transmit globulin to the circulation in significant amounts up to 20 days.4. There is a close negative correlation between body weight and total radioactivity of the sera of rats which had received doses of labelled globulin into the proximal and middle regions of the intestine. There was no such correlation after injection into the distal intestine -suggesting a restricted throughput of radioactive material by the absorptive cells of this region.5. These results are discussed in the context of the termination of antibody absorption, and in relation to the results obtained using polyvinyl pyrrolidone.

In 30‐day exposures in artificial soft water medium, survival of brown trout alevins was not affected by low pH (4.5,4.8, 5.4), by low calcium concentration (10.25 μmol l−1) or by manganese (≤20 μmol l−1), but was impaired by aluminium (6–8 μmol l−1) at low calcium concentration (10 μmol l−1) irrespective of pH (4.5 or 5.4). Manganese (6.6, 20 μmol l−1) impaired net calcium uptake and calcium deposition in the skeleton at low calcium concentration (25 μmol l−1) irrespective of pH. Aluminium (2–8 μmol l−1) impaired gross development, net uptake of calcium, potassium and sodium, and calcium deposition in the skeleton, and slightly increased the net loss of magnesium, some of these effects being more severe at calcium concentration 10 μmol l−1 than 50 μmol l−1, and some more severe at pH 5.4 than pH 4.5. Net uptake of calcium and sodium were impaired at low pH (4.5, 4.8), and skeletal calcium deposition was impaired at low calcium concentration (10 μmol l−1), but these effects of low pH and low calcium concentration were slight compared with those of the trace metals. The possible role of trace metals in reports of the deleterious effects on fish of low pH levels is discussed.

Recently hatched fry of brown trout were exposed to each of eight trace metals (Al, Cd, Cu, Fe, Mn, Ni, Pb, Zn) and to a mixture of all eight, at concentrations typical of soft acid waters, in flowing artificial soft water medium at pH 4.5 and 6.5, for 30 days. At pH 4.5, in the absence of trace metals, net uptake of Ca, Na and K and skeletal calcification were impaired but mortalities were low (10Y0). At pH 4.5, in the presence of Al, Cu, Pb and Zn individually and the mixture, mortalities were high (87-100%). Cd, Fe, Mn and Ni at pH 4.5 each caused some mortalities (1 7 4 3 % ) and impaired skeletal calcification. At pH 6.5, each of Al, Cd, Cu, Fe, Mn, Pb and the mixture of metals impaired net Ca uptake and (except Al, Fe and Pb) skeletal calcification. Net K uptake was impaired by Al and by the mixture, and less severely by Cu and by Fe. Net Na uptake was impaired by A1 and by the mixture, and less severely by Fe and by Mn. The role of trace metals other than A1 in fisheries' decline in soft acid waters is discussed.