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What is a "White Knight"?


dotti90
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These guys are still a pretty hot debate. There is much uncertainty as to what they are. The main though behind them is they are either a morph of electric blue cichlid or a hybrid between an electric blue and some variant of peacock.

Personally I now believe these guys to be an albino or melanistic variant of the electric blue cichlid. Reason I give tw possibilities as to what they are is the fish out there appear to either have red eyes (Charactoristic of albino) or black eyes (A characteristic of melanistic animals)

Perhaps someone with more knowledge regarding these can chip in. If your after pictures do a search on google. Plenty there. Also do a search of this forum. This topic has come up before.

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Its funny you said they were expensive as bay fish recently ran a front page special on them and you could pick them up for a couple of bucks wholesale.

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What are the chances of finding some in Newcastle?

I think they look nice and would like some.

Brandt

Ask one of the local shops to order you some in. They should be able to give you retail price before they order them so you knowwhat you are up for.

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how much do these normally go for in the pet shops ??

$30 ish retail.

I have an assurance from Bay Fish they are a melalin deficient Sciaenochromis fryeri not a hybrid.

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i believe that they are a true melanistic deficient electric blue.

i have a colony of these a while back, there personality, movements and physical shape were absolutely identical to an electric blue.

i read somewhere that konings does recognise them as Sciaenochromis species.

he stated that he observed a melanistic deficient electric blue at a specific location(around maleri is., nankoma is., nakantenga is. i think ).he also noted that it did not have red eyes.

ill try and find where i read that for you's..

my colony disappeared, sold them to a bloke and requested his contact details so i could get some fry back at some stage in the future. i went to ring him and the number he gave me had been disconnected.. so who knows.

if you do find some, i would love a male but..

Edited by firthy13
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There's a guy near me that was breeding them, I'll try contact him and see if he's got any fry...

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I just had my lfs order some for me, picked up a male and 2 females around 5/6cm for $23 each. They look great in contrast with the malawi I have (Mangano, Rusty's E.Y's, Peacocks) and there are no aggression problems in the tank. I really like them despite the controversy.

Zoe

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  • 3 weeks later...

Sorry to bring up an old thread but none of us can be sure of any electric blue we have here in Aus, unless you have kept your Ahli and fryeri separate since there introduction to Aus, or unless you have had them imported in. I did once here of someone in WA who has the two species in separate tanks. But the likely hood is that most out there have been crossed at some point. It has been discussed before..i'll pull up the thread when I find it.

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  • 2 weeks later...

I dont get on these forums much but here is the little I know. Apparently as I was told by an LFS owner here in Perth these guys were line bread from the Scianochromis Fryeri "Maylandi" too achive the light powder blue colour that these guys have. Here are a couple of pics of the ones that I used to have BTW they are much cheaper here. Around $11-16 for 6-8cm fish.

Male

IPB Image

Male and Female

IPB Image

Holding Female

IPB Image

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  • 2 weeks later...

if any1 is interested in the white knights let me know as i have a heap of fry from 3-8cm

i stoped breeding them as i cant keep up with the sales of males lol

im getting 85%females and 15%males out of my breeders (3m22females )

i have tryed hight p.h low p.h hight temps. low temps all the same

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I found a review article the other day because i was interested in sex determination of fish

Review article

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and

environmental inf luences by Robert H. Devlin a,*, YocraPaka Nagahama

This is what the article states in regards to temp and other factors

In mammals and birds, embryonic development at the time of sex determination occurs

under controlled temperature conditions. However, fish are poikilothermic, and embryonic

development proceeds in full exposure to the external physical environment where rela-

R.H. Devlin, Y. Nagahama / Aquaculture 208 (2002) 191–364 269

tively large temperature alterations can occur. While fish have evolved wide tolerances for

such temperature effects to allow development of viable embryos, evidence is accumulating

that effects on sex determination may occur. Temperature effects on sex have been now

observed in at least eight families of jawed fishes, as well as one Agnathan species.

Sex determination is controlled by the actions of a variety of biochemical pathways

involving many different proteins (e.g. transcription factors, steroidogenic enzymes,

receptors and second messenger systems, etc.). Since it is well known that temperature

can dramatically influence the structure and function of proteins and other macromolecules,

temperature fluctuations as are encountered by fish in different habitats could

alter sex-determination pathways and influence the probability that development would be

male or female. Temperature-dependent sex determination has been extensively studied in

reptiles, where exposure to elevated temperature results in female development in some

species (Bull and Vogt, 1979; Vogt and Bull, 1982). These temperature-dependent effects

appear to be mediated in part by influencing aromatase activity and estradiol synthesis in

females, and by steroid receptors in both sexes (Crews and Bergeron, 1994; Crews, 1996).

Such effects may also occur in fish: Estradiol secretion has been shown to range as much

as 20-fold over just a 5 jC temperature range in common carp (Manning and Kime, 1984),

and temperature also affects steroid production testis in trout, carp and tilapia (Kime and

Hyder, 1983; Manning and Kime, 1985; Kime and Manning, 1986). In Nile tilapia (O.

niloticus) and Japanese flounder (P. olivaceus), elevated temperatures (which cause

masculinization) are associated with reduced aromatase mRNA levels and lower estradiol

levels (Kitano et al., 1999; D’Cotta et al., 2001), and treatment with an aromatase inhibitor

is able to counter the masculinizing effects of high temperature (Kwon et al., 2000).

In the Atlantic silverside M. menidia, incubation of larvae at higher temperatures

increases the proportion that differentiate as males (Conover and Kynard, 1981). The

temperature-sensitive period was during the mid-larval stage, and subsequent temperature

fluxes had no effect on sex ratio, suggesting a switch-type mechanism operates to control

sex in this species (Conover and Fleisher, 1986). The temperature responsiveness of M.

menidia also has a genetic component since progeny from different females respond

differently to temperature influences (Conover and Kynard, 1981), and different sires also

can have a strong effect on temperature responsiveness (Conover and Heins, 1987a). In

nature, ocean temperatures are suspected to affect sex ratio in Menidia species such that

females are produced from earlier, colder spawning conditions, allowing additional time for

ovarian growth (Conover, 1984; Middaugh and Hemmer, 1987). This temperature responsiveness

is affected by latitude (Conover and Heins, 1987b), such that northern populations

from Canada do not respond to temperature, whereas those from South Carolina do

(Lagomarsino and Conover, 1993). These genetic differences allow distinct populations

of M. menidia to adjust sex ratios appropriately at different latitudes to maximize fitness.

Low temperature is also capable of biasing sex differentiation toward females in two

other atherinids, O. bonariensis and Patagonina hatcheri. The two species show distinctive

responses to temperature: O. bonariensis sex ratio is influenced without threshold over

a broad range of temperatures, whereas P. hatcheri sex is only influenced at temperature

extremes and otherwise has genetically determined sexes (Stru¨ssmann et al., 1996b,c). The

temperature-sensitive period for O. bonariensis (Stru¨ssmann et al., 1997) was during the

first few weeks posthatching, similar to that seen for Menidia.

270 R.H. Devlin, Y. Nagahama / Aquaculture 208 (2002) 191–364

In the loach M. anguillicaudatus, elevated temperature has been shown to skew sex

ratios towards male (Nomura et al., 1998). Masculinization was also induced by elevated

temperatures in genetically female (gynogenetic) diploids, although interestingly, some

males also rarely appeared in certain control crosses as well, suggesting that other factors

such as aneuploidy or autosomal sex factors may also influence sex differentiation in this

species. In the synchronous hermaphrodite R. marmoratus, low temperature incubation

(20 vs. 30 jC) increased the proportion of primary males from 3.8% to 74.5%, whereas

other physical variables such as salinity and illumination had no consistent effect

(Harrington, 1967; Harrington and Crossman, 1976). Recently, the lack of effect of

salinity on sex differentiation was confirmed in O. niloticus (Abucay et al., 1999).

In a comprehensive survey of temperature and pH effects on sex determination among 39

teleost species, 33 cichlid species in the genus Apistogramma (bred from field-collected

specimens) and Poecilia melanogaster (from a laboratory stock) were found to be

significantly affected by larval incubation temperature (Roemer and Beisenherz, 1996). In

most but not all cases, increasing temperature (range 23–29 jC) elevated the percentage of

males in broods. The effect of pH was less pronounced, but, in general, high pH conditions

reduced the proportion of males, in some cases to less than 10% (in A. caetei). In contrast, pH

has been found to have a significant effect on sex ratio within broods of Pelvicachromis

pulcher, P. subocellatus, P. taeniatus, Apistogramma borelli, A. caucatoides, and X. helleri,

where low and high pH produce male and female-biased broods, respectively (Rubin, 1985).

Although sex determination in tilapia species is known to be controlled polygenically

by major and minor factors on the sex chromosomes and autosomes (see Section 5.5),

temperature influences on sex ratio have also been detected (Baroiller and D’Cotta, 2000).

In Oreochromis mosambicus, genetically female groups (derived from crosses between

sex-reversed XX males and regular females) exposed to low temperature (19 jC)

incubation during early development resulted in 89% males (Mair et al., 1989). In a

similar study, O. mosambicus exposed to a range of temperatures (20–32 jC) in early

development displayed an increasing proportion of males with elevated temperature

(Wang and Tsai, 2000). In O. aureus (which has primarily a ZW system), warm

temperatures (32 jC) induced differentiation of 20% females compared to 3% observed

in controls (Mair et al., 1989), whereas more males (98% vs. 63% in controls) have been

observed at higher temperatures in other experiments (Desprez and Melard, 1998b).

Fluctuating temperature regimes also can induce masculinization, but less effectively than

a constant high (35 jC) temperature (Baras et al., 2000). In O. niloticus, elevated

temperature generally has a masculinizing effect that is affected by, and can override,

genetic influences on sex determination (Baroiller et al., 1995, 1996; Baras et al., 2001),

but a feminizing effect has also been observed in all-male and YY strains of O. niloticus,

particularly in inbred vs. outbred strains (Abucay et al., 1999). Environmental conditions

are anticipated to have variable effects on sex differentiation depending on the genetic

background and developmental stability of different strains. These observations imply that

sex determination is very labile in different tilapia species and that, depending on the exact

combinations of genetic modifiers present in different strains, environmental effects on sex

determination may be variable in strength and direction, and may also be very sensitive to

the level of inbreeding and consequent developmental stability within a strain (Purdom,

1993; Abucay et al., 1999). Temperature lability may provide evolutionary advantages to

R.H. Devlin, Y. Nagahama / Aquaculture 208 (2002) 191–364 271

tilapia species by providing higher numbers of males with increased capacity for dispersal

(Baras et al., 2000), but would also be expected to affect the establishment of sex

chromosomes with complete control over the sex determination process and would also

result in the accumulation of balancing autosomal genetic factors.

Genetic effects on temperature responsiveness have also been detected in Poeciliopsis

lucida, a viviparous species: Exposure of embryos from a sensitive strain to elevated rearing

temperatures before parturition can bias the sex ratio towards males (Schultz, 1993). Analysis

of F1 progeny derived from reciprocal crosses between responsive and nonresponsive

strains also showed that this effect arises primarily from the genotype of the progeny rather

than from maternal influences. Recently, elevated temperature has been shown to have a

masculinizing effect on sex determination in the honmoroko, Gnathopogon caerulescens

(Fujioka, 2001), a species with primarily an XX/XY system of sex determination. In this

study, intersexes could be sex-reversed. XX males were positively identified by progeny

testing, and significant family effects were found to influence sex ratios at normal temperatures

as well as the response to masculinizing effects of elevated temperatures.

In Anguilla, low-temperature incubation did not affect sex ratio in A. rostrata (Peterson

et al., 1996), whereas male-biased sex ratios appear to be slightly enhanced by elevated

larval incubation temperatures (Holmgren, 1996) in A. anguilla or by high stock densities

in both species (Roncarati et al., 1997; Krueger and Oliveira, 1999). Based on field studies

of lamprey (where gonadal differentiation can change during development; Lowartz and

Beamish, 2000), environmental factors may influence sex ratio such that elevated

temperatures reduce the incidence of males under high-growth conditions or lower

population densities (Beamish, 1993; Docker and Beamish, 1994). In other fish where

temperature influences on sex ratio have been specifically examined, no effects have been

observed, including northern populations of F. heteroclitus and Cyprinodon variegatus

(Conover and Demond, 1991), the mosquitofish (G. affinis) (Bennett and Goodyear,

1978), and the bloater (Coregonus hoyi) (Eck and Allen, 1993).

In other fish, indications of temperature-dependent sex determination have been

suggested. In channel catfish Ictalurus punctatus, sex is normally determined genetically

by an XY system, but high temperature extremes applied during the critical period for sex

determination result in female-skewed sex ratios, which indicate influence by environmental

factors as well (Patino et al., 1996). In sockeye salmon (Oncorhynchus nerka), a

temperature elevation occurring during embryonic development has been associated with a

female-biased sex ratio (Craig et al., 1996), and similarly, elevated temperatures are

associated with female-biased sex ratios in Epiplatys chaperi (Van Doorn, 1962) and G.

aculeatus (Lindsey, 1962). At normal rearing temperatures (25 jC), the sex ratio of sea

bass (D. labrax) populations is normally male biased, but low-temperature incubation (15

jC) during the labile period of gonad development results in all-male populations

(Bla´zquez et al., 1998b; Pavlidis et al., 2000). In contrast, in hirame P. olivaceus, high

temperature reduced the numbers of females (Tabata, 1995; Yamamoto, 1999), and in the

barfin flounder V. moseri, a difference in rearing temperature from 14 to 18 jC near the

time of gonadal differentiation results in equal sex ratios in the former to all male progeny

in the latter (Goto et al., 1999). In marbled sole, Limanda yokohamae, masculinization has

also been shown to be induced by elevated (25 vs. 15 jC) temperatures (Goto et al.,

2000a), as have goldfish and black rockfish S. schlegeli (Goto et al., 2000b; Lee et al.,

272 R.H. Devlin, Y. Nagahama / Aquaculture 208 (2002) 191–364

2000). Some temperature effects on sex determination may be quite subtle (e.g. in atipa

Hoplosternum littorale), detectable only by careful examination of intrafamily responses

that are otherwise masked in populations by genetic variance among different families

(Hostache et al., 1995). A discussion of other factors (day length, radiation, water quality,

crowding, fertilization timing) reported to influence sex ratio has previously been

presented (Chan and Yeung, 1983).

The above studies clearly reveal that sex determination can be influenced by external

physical variables such as temperature in most fish families examined. In some cases, the

species utilize these influences as a strategy to improve reproductive success, whereas in

others, the effects on sex determination may not occur naturally, and may arise from

disruptions of normal sex-determination processes under extreme environmental conditions.

Indeed, the viability of germ cells of two species of fish (O. bonariensis and P.

hatcheri) have been shown to be sensitive to elevated temperatures (Stru¨ssmann et al.,

1998), suggesting that pathological effects on gonadal development may indeed occur.

Similarly, temperature has been found to influence expression of a SRY-related Sox gene in

a reptile (Western et al., 1999).

cheers

John

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