The influence of salinity and temperature change on the functioning of the urinary bladder in the early larval stages of the atlantic herring Clupea harengus L.

Major changes in the morphology of the urinary bladder were observed during the transition from yolk-sac to feeding larval stages of herring, in particular bladder volume increased almost sixfold. Initially, the urine flowed into the hindgut, but within days of hatching a separate urinary duct, leading to the exterior, had formed. Micturation was intermittent but quite regular. The period between micturations increased from 1.6 to 4 min in the progression between the two larval stages. The discharge volume was approximately 50 % of the full bladder volume in all stages studied. Urine flow rate (UFR) in sea water rose slightly from 1 to 1.7 nl mg(-)(1 )h(-)(1) during early larval development. Exposure to low salinities significantly reduced UFR in yolk-sac larvae, but in the later stages UFR increased significantly in hypo-osmotic salinities, so that UFR in 4 salinity was 2.5 times that in 34 salinity. The main variable influencing UFR was discharge frequency. Cardiac output was not influenced by salinity and was considered not to be a controlling factor in the UFR response to salinity change. UFR increased with temperature with Q(10) of 2.3 in stage 1 larvae and 1. 5 in stage 2 larvae, over 7-15 degrees C.

Inducibility of metallothionein mRNA expression and cadmium tolerance in larvae of a marine teleost, the turbot (Scophthalmus maximus).

An acute (48-hr) lethal toxicity study of turbot at various stages from hatch to juveniles showed that prior to first exogenous feeding, larvae of turbot were an order of magnitude more sensitive to cadmium toxicity than later developmental stages (LC50 of 0.18-0.23 ppm Cd versus 2-5 ppm Cd). To investigate the possible role of metallothionein (MT) in Cd tolerance, the concentrations of MT mRNA were determined in control and Cd-exposed animals using a plaice MT cDNA probe. MT mRNA was expressed throughout embryonic and early larval development at levels approximately twice those in juvenile turbot liver apart from the period around hatching, when there was a decreased level of expression. During endogenous feeding, despite larval drinking, MT mRNA levels did not appear to be inducible by exposure to Cd in the water within 3 days of hatching but were induced three- to fivefold after 48 hr exposure to waterborne Cd at all later stages of development. The results suggest that Cd tolerance is associated with metal induction of MT gene transcription and that the enhanced sensitivity of very early stage larvae is attributable to a deficiency in MT gene transcription.

Hypoosmoregulation of larvae of the turbot, Scophthalamus maximus: drinking and gut function in relation to environmental salinity.

Measurement of blood osmolarity of pre-metamorphic turbot larvae demonstrated that hypoosmoregulation is well established in larvae 6 days post-hatch (121 degree-days) and older. Blood osmolarity of 121-420 degree-day larvae reared in 100% seawater was significantly greater than blood osmolarity of larvae reared in 50% seawater. Hypoosmoregulation involved drinking, but instantaneous drinking rates of 340 degree-day larvae reared in 100% seawater were only slightly more than those of similarly aged larvae reared in 50% seawater. Adaptation to environmental salinity involved changes in gut water absorption; 65-74% water absorption occurred in larvae reared in seawater compared to 30-35% water absorption in larvae reared in 50% seawater. Gastrointestinal water absorption occurred prior to the rectum. In seawater this occurred alongside a decrease in gut fluid osmolarity but desalting was apparently less significant than in adult fish. Absolute water absorption by the gut of 340 degree-day larvae reared in seawater was about 2-fold that of larvae held in 50% seawater, while the osmotic gradient between internal body fluids and environmental media differed by 4-fold, which implies changes the in water permeability of skin and/or developing gills.

Morphology of the pronephros of the juvenile brown trout, Salmo trutta.

The pronephros in juvenile brown trout (Salmo trutta) consists of a large ovoid renal corpuscle and a pair of tubules. The corpuscle is retained for 11 months, after which the glomerulus regresses. The glomerular arteries come directly from the dorsal aorta. The interstitium is permeated with venous blood vessels that arise from the anterior cardinal veins and are closely apposed to the tubules. Two distinct segments of the pronephric tubular system are distinguished by the histological and ultrastructural features of their component cells: 1) a short, transitional neck in which cells change from capsular epithelium to columnar epithelium, typical of tubules; 2) the convoluted segment composed of cells similar to first proximal tubular cells of the opisthonephros with well-formed brush borders, apical vesicles that vary in size and number along this segment, and lysosomes. Pinocytosis and exocytosis are also evident in this segment. The tubular system increases in length and in its convolutions until about week 9, when the opisthonephros develops. Distally each tubule connects with a Wolffian duct, with cells marked by the absence of apical inclusions and the presence of a uniform brush border, numerous mitochondria, and elaborate infolding of the basalar membrane. Nephrostomes, which are often characteristic of pronephroi, are not present. Cells with long cilia are found throughout the tubular system but are most characteristic of the neck and Wolffian-duct segments.

The structure of the head kidney in the mudskipper, Periophthalmus koelreuteri (pallas).

The head kidneys of adult Periophthalamus koelreuteri contain many functional glomerular nephorns which on the basis of this histochemical study, are indistinguishable from those of the typical opistonephros of marine teleosts. The anterior lobes resemble, in location and in the presence of intertubular erythropoeitic tissue, the pronephros in other species. The single nephron found there, however, does not differ significantly from the other nephrons of the head kidney. It is suggested, therefore, that the nephrons of the head kidney in this species are opisthonephric in origin.

New developments in ultrasonic fish tracking.

A range of small, long-life ultrasonic fish tags is described and their use illustrated with an improved system of fixed hydrophone tracking stations. A boat-mounted hydrophone system giving bearing and range estimations for use in open-water fish tracking is described together with a portable hand-held unit for simple location of tagged fish in rivers, etc. Typical results based on intensive use of these systems are given.