Treatment with thiamine hydrochloride and astaxanthine for the prevention of yolk-sac mortality in Baltic salmon fry (M74 syndrome)

Abstract

Two practical methods are reported for treating feral Baltic salmon with thiamine hydrochloride against M74 syndrome (abnormally high yolk-sac fry mortality of the Baltic salmon). Both bathing of the yolk-sac fry in thiamine hydrochloride (1000 mg 1-l, 1 h) and a single intraperitoneal injection given to the female brood fish (100 mg kg-' fish) during the summer 3 mo before stripping were shown to elevate the whole body total thiamine concentration in the fry. Both treatments were also shown to be effective in preventing mortality due to M74 syndrome. The effect of bathing the yolksac fry was shown to be dose-dependent. The results support the view that there is a causal relationship between the thiamine status of the yolk-sac fry and M74 mortality. An intraperitoneal injection of astaxanthine suspension administered to the female brood fish (11 mg kg-' fish) in the summer 3 mo before stripping elevated the astaxanthine concentration in the eggs but did not affect mortality due to M74 syndrome. An interaction between astaxanthine and thiamine may occur in the developing embryo or yolk-sac fry, however. No association could be demonstrated between the various thiamine hydrochloride treatment practices and hepatic cytochrome P450 dependent 7-ethoxyresorufin-Odeethylase (EROD) activity in the yolk-sac fry. An injection of thiamine hydrochloride into the peritoneal cavity of w-dd Baltic salmon females could be used to raise thiamine concentrations in their offspring in the rivers. The effect on smolt production in Finnish Baltic salmon rivers needs to be investigated further, however.

Parental Background Predisposes Baltic Salmon Fry to M74 Syndrome

“…This is also typical for M74 (see e.g. [8]). The cumulative yolk-sac mortality of the offspring of the farmed females can be regarded as typical for farmed salmon at the Lautiosaari State Fish Hatchery (unpublished statistics of the farm).…”

“…In this study the broodfish were all of the same strain, which makes a genetic aetiology even more unlikely than in the larger material of [12,8] found that injection of female broodfish with astaxanthine caused a proportionally greater decrease in thiamine concentration during the development of their offspring from newly fertilized eggs to yolk-sac fry. There might be also other effects of this kind on thiamine metabolism, some of which could be mediated by the male.…”

“…[8]). [4] reported that M74 syndrome in Baltic salmon in Swedish rivers was bound to the females, while milt from wiggling males – fish showing symptoms of a thiamine related-illness [10,1] – produced healthy offspring.…”

“…The wild fish were caught from the Bothnian Bay at the mouth of the River Simo in summer 1993 and kept under similar conditions to the broodfish described in [8]. Farmed broodfish of the River Simo strain of the Baltic salmon were held at Taivalkoski Game and Fisheries Research (males) and River Simo State Fish Farm (females) and were fed on standard commercial dry salmon pellets.…”

“…The water-hardened eggs were disinfected with an iodophor (100 ppm free iodine for 10–15 min) and the eggs from each crossing were incubated separately. The development of yolk-sac fry was followed as described in [8]. The eggs of three crossings died during incubation; all other groups of eggs originating from the same broodfish were then excluded.…”